/ Agriculture Handboo-k No. 134 QUEFNS BOROUGH PUBLIC LIBRARY AUG 3 1976 i'epository Document MAPLE SIRUP PRODUCERS MANUAL UNITED STATES DEPARTMENT OF AGRICULTURE • AGRICULTURAL RESEARCH SERVICE From the collection of the n m 0 Prejinger V Jjibrary t P San Francisco, California 2008 AGRICULTURE HANDBOOK NO. 134 MAPLE SIRUP PRODUCERS MANUAL By c. o. waiits and Claude H. Hills Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE Issued November 1963 Revised June 1965 Washingtoa D.C. Slightly revised July 1976 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $2.50 25% discount allowed on order of 100 or more to one address Stock Number 001-000-03504-5 ACKNOWLEDGMENTS The authors acknowledge the technical assistance of M. C. Audsley, H. G. Lento, A. J. Menna, T. S. Michener, J. Naghski, W. L. Porter, E. E. Stinson, and J. C. Underwood of the Eastern Regional Research Center, Agricultural Research Service; and F. E. Winch, Jr., Cornell University; the research work of J. W. Marvin and his associates at the University of Vermont; P. W. Robbins and R. N. Costilow and their students at the Michigan State University; and John Hacskaylo and James Callander, Ohio State Experiment Station; the cooperation of Lloyd M. Sipple, Bainbridge, N.Y., in developing and testing new equipment and procedures; and the facilities and equipment made available by the following maple sirup producers and equipment manufacturers; John Zimmerman, George Keim, Rey- nolds Sugar Bush, A. C. Lamb and Sons, Grimm Evaporator Company, Vermont Evaporator Company, George Soule Company, Gary Maple Sugar Company, and General Foods Corporation. The authors express their thanks for the assistance, support, and encouragement given in the preparation of this handbook by the National Maple Syrup Council, P. A Wells, C. F. Woodward, and Mrs. PhyUis K Davis. Trade names are used in this handbook solely to provide specific information. Mention of a trade name does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture or an endorsement by the Department over other products not mentioned CONTENTS Economics ^ 3 Sugar maples 4 The sugar grove 4 Sap yields 6 Summary 8 Tapping the tree 8 Date of tapping 9 Selecting trees 9 Boring tapholes 9 Life of a taphole 11 Sanitizing tapholes 12 Summary 14 Spouts and buckets 14 Sap spouts 14 Rainguards 16 Sap buckets and bags 16 Summary 18 Collecting the sap 18 Collecting tanks 19 PipeHnes 20 Summary 22 Plastic tubing 23 Installing tubing 24 Taking down tubing 28 Washing and sanitizing tubing 29 Reinstalling tubing 33 Summary 34 Vacuum systems 35 Storage tanks 35 Summary 37 Evaporator house on the sap-producing farm 37 Location 37 Function 38 Requirements 38 Design 38 Steam ventilation 38 Location of evaporator 41 Air supply 42 Sirup-processing room 42 Fuel storage 42 Summary 43 The evaporator and its function 43 Design of evaporator 44 Changes in sap during its evaporation to sirup 44 Evaporation time 45 Liquid level in evaporator 46 Rates of evaporation 47 Rule of 86 48 Summary 48 Operating the evaporator , 49 Starting the evaporator 49 Drawing off the sirup 49 Finishing pan 50 Page Automatic drawoff 51 End of an evaporation 52 Cleaning the evaporator 53 Summary 55 Other types of evaporators 55 Steam evaporator 55 Vacuum evaporator 57 Summary 57 Fuel 58 Wood 58 Oil 58 Summary 65 Maple sirup 65 Composition of sap and sirup 65 Color and flavor 67 Buddy sap and sirup 68 Rules of sirupmaking 70 Grades of sirup 70 Summary 71 Control of finished sirup 71 Viscosity of maple sirup 71 Effect of temperature on viscosity 72 Old standards of finished sirup V2 Use of precision instruments 72 Elevation of boiling point 72 Finishing pan 74 Special thermometers 75 Hydrometers 76 Summary 78 Clarification of sirup 78 Sugar sand 78 Sedimentation 79 Filtration 79 Summary 81 Checking and adjusting density of sirup 82 Weight method 82 Refractometry method 82 Hydrometry method 82 Measuring density 85 Measuring solids content 86 Adjusting density 87 Summary 88 Grading sirup by color 89 Color standards 89 U.S. color comparator 89 Summary 90 Packaging 90 Stack burn 91 Control of micro-organisms 91 Size and type of package 92 Summary 92 Standards for maple sirup for retail sale 93 Summary 94 m Maple products 94 Equipment 95 Maple sugar 96 Maple cream or butter 98 Fondant 100 Soft sugar candies 100 Maple spread 105 Fluffed maple product 106 High-flavored maple sirup 106 Crystalline honey- maple spread 109 Other maple products ^ 109 Summary 110 Testing maple sirup for invert sugar 113 Simple test H"^ Quantitative test 114 Determining invert sugar content of sirup 115 Summary 115 PaRC The central evaporator plant 116 Location 117 Size 117 Design 117 Operation 118 Sap suppliers 120 Purchase of sap 121 Storing sap 122 Handling and storing sirup 124 Sanitation 125 Economics 125 Standardizing sirup for color and density 126 Custom packaging and gift packages 126 High-flavored and high-density sirup 127 Manufacture of confections 127 Summary 128 References cited 128 Supplemental reading 134 MAPLE SIRUP PRODUCERS MANUAL By C. O. WILUTS" and CLAUDE H. HILLS, Eastern Regional Research Center, Northeastern Region, Agricultural Research Service No one knows who first discovered how to make sirup and sugar from the sap of the maple tree. Both were well-estabhshed items of barter among the Indians Hving in the area of the Great Lakes and the St. Lawrence River, even before the arrival of the white man {36, 10 IV The maple crop, one of oui- oldest agricultural commodities, is one of the few crops that is solely American. Until only a few years ago, it was both produced and processed entirely on the farm. The last 20 years have witnessed some vast changes in the maple sirup industry. For the first half of this century, maple sap was col- lected and converted to sirup in much the same way as it was in 1900, when atmospheric evapo- ration equipment was developed by Yankee ingenuity (56). Many of the more recent changes have been the result of scientific and engineering studies carried out by the Eastern Regional Research Center in Philadelphia, Pa., and by the experiment stations and agricul- tural colleges of Michigan, New Hampshire, New York, Ohio, and Vermont. Recently the Forest Service has established a facility for research on maple sirup production at the Northeastern Forest Experiment Station in Burlington, Vt. Maple sirup is a woodland crop. Since the trees grow best at altitudes of 600 feet and higher, maple sirup is usually produced in hilly country. Its production is a vital part of the local economy in dozens of communities from Maine westward into Minnesota, and south to Indiana and West Virginia (chart 1). The same type and quality of maple products are pro- duced throughout the area. ' Retired February 1969. - Italic numbers in parentheses refer to References Cited, p. 128. Chart l.^A and B , range of hard maple trees; A, range of commercial production of maple sirup. Maple sirup, like other crops, is subject to yearly fluctuations in production because of climatic and economic conditions. Production in the past has been affected by the cost or supply of white sugar and by the supply of farm labor. In 1860, a record crop of 4,132,000 gallons of maple sirup was produced. For the next decade the price of cane sugar declined. Production of maple sirup also declined to a low of 921,000 gallons in 1869. As cane sugar became scarce during World War I, production of maple sirup again rose, slightly exceeding the 1860 record. Production also increased during World War II. Since then, production has decreased (table 1) (125, 126). The decreased production since World War II is a reflection of the shortage of farm labor 2 AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE Table L — Maple sugar and sirup: Trees tapped, production, average price received by farmers, and imports. United States, selected years, 1918-70 ' Trees tapped Production Price ' Imports for consumption Year Sugar made Sirup made \ Total product in terms of sugar ■ , Average total product per tree As sugar ' As sirup - Per pound - of sugar Per gallon of sirup Sugar Sirup ' 1918 1,000 trees .. 17,053 .- 14,070 .- 13,158 - 12,341 ._ 9,970 - 7,685 -- 8,090 __ 6,138 1,000 pounds 11,383 3,238 2,134 1,241 394 202 246 1,000 gallons 4,141 2,817 3,712 .3,432 2,601 1,030 2,006 ■■^ 1,578 ^ 1,124 1,266 1,110 1,000 pounds 44,511 25,774 31,830 28,697 21,202 8,442 16,302 12,624 8,992 10,128 8,880 PouTids 2.61 1.83 2.42 2.33 2.13 1.10 2.02 Gallons 0.33 .23 .30 .29 .27 .14 .25 .26 Cents Dollars 1,000 pounds . 3,807 3,911 9,735 1,920 4,087 4,131 6,549 6,024 5,742 4,688 3,561 1,000 pounds 1925 1930 1935 1940 1945 1950 1955 26.9 30.2 26.7 29.4 54.6 77.2 2.08 2.03 1.42 1.65 3.21 4.12 4.68 4.96 5.04 6.83 113 1,575 2,469 4,660 1,232 5,282 5,044 10,009 9,700 10,549 1960 1965 1970 ' For 1918-40, production estimates for Maine, Maryland, Massachusetts, Michigan, New Hampshire, New York. Ohio, Pennsylvania, and Vermont; in 1945 Minnesota was added. - Assuming that 1 gallon of sirup is equivalent to 8 pounds of sugar. 'Obtained by weighting State prices by quantity sold from 1945 to date; prior to 1945 weighted by production. I A gallon of sirup weighs about 11 pounds. ' Includes sirup later made into sugar. SOURCES: Data for 1918-50 from Agricultural Statistics, 1957, table 133 {125). Data for 1955 and 1960 from Statistical Reporting Service and Economic Research Service, for 1965 and 1970 from Agricultural Statistics, 1972. table 137 (128). during this period. Although the trend in the country as a whole is downward, production of maple sirup in Michigan, Minnesota, and Wis- consin has increased. In fact, based on the number of tappable trees, production in these States could exceed production in New York and the Northeastern States. For example, Michigan has one-fifth of the total stand of maple trees. Canada's total maple crop is about double that of the United States. Table 2 shows the number of maple trees of tappable size and the percentage tapped in 1951. Surveys in the eastern maple-producing areas (126) of the number of maple trees tapped as well as the total number of tappable size have shown that the industry is not suffering from too few trees. Although many sugar ma- ples have been cut for lumber, vast stands remain, and these stands can supply our maple sirup needs. Table 3 shows the production of maple sugar by the 11 principal States for selected years, 1926-71. Table 2. — Tappable maple trees, and trees tapped. Eastern States, 1951 State Tappable trees ' Trees tapped Thousands Number Percent Maine 53,553 136,000 0.25 Maryland 1,660 28,000 1.7 Massachusetts 11,913 166,000 1.4 New Hampshire 12,103 261,000 2.2 New York 73,128 1,960,000 2.7 Pennsylvania 33,553 422,000 1.3 Vermont 25,840 3,118,000 12.1 West Virginia 13,031 ' Larger than 10 inches in diameter at breast height. MAPLE SIRUP PRODUCERS MANUAL Table 3.— Rank of States in production of maple sugar, selected years, 1926-71 Rank 1926 1931 1936 1941 1946 1951 1956 1961 1966 1971 1 N.Y. Vt. N.Y. Ohio Pa. Mich. Wis. N.H. Mass. Md. Maine Vt. N.Y. Ohio Pa. Mich. Wi^. N.H. Mass. Md. Maine Vt. N.Y. Ohio Pa. Mich. Mass. N.H. Wis. Maine Md. Vt. N.Y. Ohio Mich. Pa. N.H. Mass. Wis. Maine Md. Vt. N.Y. Pa. Mich. Mass.. N.H. Wis. Maine Md. Ohio _Minn. Vt. N.Y. Ohio Pa. Wis. Mich. N.H. Mass. Md. Maine Minn. Vt. N.Y. Ohio Wis. Mich. Pa. N.H. Mass. Md. Maine Minn. N.Y. Vt. Wis. Pa. Mich. Ohio N.H. Mass. Md. Minn. Maine N.Y. 2 -. Vt. Vt. 3 - Ohio Ohio 4 Pa. Pa. 5 Mich. Mich. 6 N.H. Wis. 7 Mass. N.H. 8 _. Wis. Mass. 9 Maine Maine 10 11 Md. ECONOMICS Maple sirup, a noncultivated, nonfertilized crop derived from trees of the farm woodlot, provides supplemental cash incomes for many farmers, and it is the major cash crop for some farmers {2A, 26, 132, lUO, U2). The trees on 1 acre will provide 160 tapholes and an average yield of 1 quart of sirup per taphole, or 40 gallons of sirup per acre. At $10 per gallon, this sirup provides an annual per-acre gross income of $400. With the advent of the central evaporator plant, maple sap became a marketable commod- ity. Annual gross income for sap ranges from 900 to $2.50 per taphole for sap delivered at the evaporator plant. The maple season is short and comes in the early spring when most other farm activities are slowest. Thus, it does not compete with other farm activities. Because the season oc- curs when off-farm employment is at a seasonal low, it fits well into a part-time farming pro- gram. Surveys in New York (5, 8), Ohio (63), Michi- gan {92), and Wisconsin (113) have shown that earnings from the production of maple sirup are among the highest on the farm. Wages average $3 per hour with a high of more than $5 for every hour spent in cleaning equipment, tapping trees, installing and taking down equip- ment, and collecting and boiling the sap. With the high annual cash crop and high wages earned in producing sap and sirup, it is difficult to understand why only 1 of 20 tappa- ble maple trees is being utilized. However, until recently maple sirup production methods were antiquated, at least when compared to modern methods of crop and livestock farming, and the unfavorable working conditions made sap col- lection and sirupmaking unattractive. Both equipment and processing methods are being modernized. Modernization should do much toward making maple sap and sirup pro- duction more attractive (71, U3). This moderni- zation includes plastic pipelines for collecting and transporting sap; taphole germicidal pel- lets; sanitary practices in tapping and sap han- dling; oil-fired evaporators; improved methods for evaporating sap, filtering sirup, and packag- ing the products; and the central evaporator plant. All these changes have reduced labor requirements and production costs, and have contributed to producing better grades of sirup that have a correspondingly greater value. Be- cause of the relatively high fixed costs for producing sirup on the farm, net income may be too low when sap from fewer than 500 tapholes is available, and the sap could be more profita- bly sold to a central plant. Sirup can be sold immediately to produce ready cash, or it can be held for a more favora- ble market or as a supply of raw material for producing more profitable maple products. If the sirup is held, it can be used as collateral for short-term loans. Since 1940, the proportion of the maple sirup produced in the United States that has been sold directly to the consumer by the producer AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE has increased. In many instances this has in- creased returns for the producer. To stabilize this expanded outlet, the producer has im- proved the appearance of the package and the quality of the sirup so that it meets State and Federal specifications. Many producers are ob- taining larger returns by converting their sirup to confections such as maple cream and hard and soft sugar candies. "^ Maple sirup producers" have formed associa- tions so they can pool their stocks. The chief functions of these associations are to maintain adequate supplies, to promote sales, and to maintain the quality of the products. A number of communities hold annual festivals to stimu- late interest in maple items. The central evaporator plant has made it possible for the first time to separate sap pro- duction from the processing of sap to sirup. Thus, farmers can realize a substantial income from maple sap without having to make large capital investments m an evaporator house, an evaporator, sap storage tanks, and miscella- neous equipment. The States, in cooperation with the Agricul- tural Research Service and the Extension Serv- ice of the U.S. Department of Agriculture, are conducting strong extension programs. These programs have brought the results of research directly to maple producers. In New York, a leader in this progranri, it is not uncommon for more than a thousand producers to attend the annual "maple sirup" schools held throughout the State in the premaple season. SUGAR MAPLES Only 2 of the 13 species of maple (Acer) native to the United States are important in sirup production (6, 55, 12i, 157). Acer saccharum Marsh, (better known as sugar maple, hard maple, rock maple, or sugar tree) furnishes three-fourths, of all sap used in the production of maple sirup. Although this tree grows throughout the maple-producing areas (chart 1), the largest numbers are in the Lake States and the Northeast. Trees grow singly and in groups in mixed stands of hard- woods. The trunk of a mature tree may be 30 to 40 inches in diameter. The tree is a prolific seeder and endures shade well but unfortu- nately does not grow rapidly. It is best distin- guished by its leaf (chart 2). Acer nigrum Michx. F. (black sugar maple, hard maple, or sugar maple) grows over a smaller range than does A. sacchamm. It does not grow as far north or south but is more abundant in the western part of its range. This tree is similar to A. saccharum in both sap production and appearance. Its principal distin- guishing feature is the large drooping leaf of midsummer (chart 2). Other species of maples commonly found in our hardwood forests are the red maple Acer rubrum L.) and the silver maple (A. saccha- rinum L.). These trees, readily identified by their leaves (chart 2), are not good sources of RED MAPLE "' SILVER MAPLE Chart 2. — Leaves of the sugar maple (Acer saccharum Marsh.), red maple (A. rubrum L.), silver maple (A. saccharinum L.), and black maple (A. nigrum Michx. F.). maple sirup because their sap is less sweet than that of A. saccharum and A. nigrum, and it often contains excessive amounts of sugar sand. The red maple, the more common of the two, is easily identified in the spring by the red color of its buds. The Sugar Grove Most maple sugar groves, commonly called sugar bushes, are parts of stands of old hard- MAPLE SIRUP PRODUCERS MANUAL wood forests. In the ideal sugar grove, most of the other trees have been cut out and the maples have been thinned sufficiently to allow the trees to develop a good crown growth (,63). Thinning should be done according to a care- fully planned program, with the assistance of the State extension forester and the State for- ester for the area. If the stand is made up entirely of maples, approximately the same vol- ume of sap is produced per acre regardless of the size of the trees (^6). As the number of trees per acre decreases below 160 trees 10 inches in diameter at breast height (d.b.h.) or 40 trees 25 inches d.b.h., the size of the crovvTis and the yield per tree may increase but the cost of collecting sap also increases because the dis- tance between trees requires longer sap mains when tubing is used, and sap collected by hand must be carried farther. Figures 1 and 2 show a maple grove with the large full crowns that are so important to the production of large amounts of sweet sap. For maximum returns, the grove should con- tain at least SOOtapholes, that is, a minimum of 500 trees 10 inches d.b.h. Groves with fewer than 10 maple trees per acre are not profitable; groves with 30 to 40 trees 25 inches d.b.h. are ideal (<54). Maples grown in the open — for example, along the roadside (fig. 3) — are excellent sap producers (6Jf, 65, 67) not only because they have large crowns but also because they have a large leaf area, which is necessary for both starch and sugar production. Because of their shorter boles, roadside trees do not make as good saw logs as do trees that grow under crowded conditions. Studies have been con- ducted on the effect of fertilization {^6). Trees in a crowded stand have smaller crowns and therefore are not good sap produc- ers (figs. 4 and 5) because of their reduced leaf area. The ideal sugar grove (figs. 6 and 7) requires not only a planned spacing of trees but also a good understory to protect the ground, keep it moist, and permit growth of seedling maples to replace mature trees that should be cut down (fig. 8). Often these mature trees can be sold for lumber. However, there is no such thing as a dual-purpose maple tree — one that serves PN-469S Figure 1. — Grove of maple trees v/ith large crowns.which are needed for large yields of sweet sap. PN-4699 Figure 2. — Same grove shown in figure 1 after defoliation, showing the branch structure of trees with large crowns. AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN-4700 Figure 3. — Large-crowned maples, typical of roadside trees. PN-noi Figure U- — Trees in a crowded stand have small crowns and small boles. This ^rove requires thinning before it will be a profitable source of maple sap. equally well as a sap producer and as a source of lumber — because the factors favoring the growth of trees for the two purposes are not compatible. Consult your State extension forester, farm forester, and county agent and work with them to develop a management plan for your sugar grove. Aim for 160 tapholes per acre. PN-4881 Figure 5. — Mixed stand of crowded trees. Some trees have long boles and small crowns. They make good saw logs but are poor sap producers. PN-no2 Figure 6. — An ideal spacing of maple trees, favoring the growth of large crowns. Sap Yields The yield of sap in a sugar grove should be expressed in terms of the number of tapholes rather than the number of trees. The yield per hole is independent of the number of holes per MAPLE SIRUP PRODUCERS MANUAL PN-4703 Figure 7. — This grove shows the effect of heavy grazing, a practice not recommended since it results in reduced sapwood production, stag-headedness, loss of reproduc- tion, and root damage caused by soil compaction. PN-170-1 Figure 8. — Removing overmature trees that produce sap low in sugar content, to encourage growth of young stock. The high cut is made to avoid some of the sap stain and diseased wood associated with old tapholes. tree. A mean range per taphole is from 5 to 15 gallons {95). However, a single taphole often produces from 40 to 80 gallons of sap in a single year — the equivalent of 3 or more quarts of sirup. The sugar content of the sap produced by different trees in a grove varies considerably (45, 110). The sap produced by the average tree has a sugar content of 2° to 3° Brix.^ Frequently ' The density of sap and sirup is due to a mixture of dissolved solids and not just to sugar. The physical in- struments used to measure the density of sap and sirup do not distinguish between the density due to sugar and that due to other solids. The degrees Brix (° Brix) means that the solution has the same density as a solution containing a percentage of sugar numerically equal to the Brix value. trees produce sap with a sugar content of less than 1° Brix, and occasionally a tree produces sap with a sugar content of 9° or even 11° Brix. A conservative estimate is that the sap from four tapholes will yield 1 gallon of sirup. This sap most likely would have a density of 2.2^" Brix. Thus, 10 gallons of sap from each taphole would be required to yield 1 gallon of sirup. No device has been developed that will enable a maple sap producer to determine when sap will begin to run. However, sap will flow from the tapholes over a period of several weeks. The greatest yield of sap may be produced in a single run that occurs at the beginning of the period, at any time during the period, or at the end of the period. In 1960 almost all the sap crop was collected in a 24- to 48-hour period and the Brix value of the sap was much higher than 2.2°. Many producers reported sap of 5° Brix and higher. Because of the large volume of sap collected in this short period, many producers reported that their buckets overflowed. How much was lost will never be known. This loss would not have occurred had plastic tubing been used for collecting and transporting the sap. Because of the large yield of sap in 1960 and its high sugar content, many producers who sold their sap to central evaporator plants re- ceived as much as $1.90 per taphole. A yield per taphole of 10 gallons of 5°-Brix sap having a value of 19.5 cents per gallon gives $1.95 per taphole. On this basis, a sugar grove with only 100 tapholes per acre would produce a gross of $195 per acre. This may answer the question that has often been raised as to whether the sugar orchard should be operated to produce sap or should be cut and sold as lumber. The yield and sweetness of the sap produced by a tree vary from year to year, but trees that produce sap with a high sugar content and trees that produce sap with a low sugar content maintain their relative positions from year to year {112). It is important to know the exact sugar content of the sap produced by each tree. Measuring the sugar content of sap is not difficult. All that is needed is a sap hydrometer or refractometer and a thermometer. To make the reading, float the hydrometer in the sap bucket or in a hydrometer can contain- ing the sap (fig. 9). Also, obtain the temperature AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN-4706 Figure 9. — Measuring the density of sap C Brix) with a precision hydrometer cahbrated in 0.1°. If the bucket contains too little sap to provide the necessary depth for the measurement, transfer the sap to a hydrometer can. of the sap so the hydrometer reading can be corrected. (The sap should contain no ice.) Sub- tract 0.4° Brix for temperatures of 32f to 50° F., 0.3° Brix for temperatures of 51° to 59°, and 0.1° Brix for temperatures of 60^ to 68". The sap hydrometer is usually calibrated from 0° to 10° Brix, with divisions of 0.5°. A more accurate measurement can be obtained by using a hydrometer with divisions of 0.1° (fig. 9). The amount of sugar in sap is of great eco- nomic importance. A taphole that produces 15 gallons of sap with a sugar content of 2° Brix yields 2.5 pounds of sugar, or one-third gallon of sirup; whereas a taphole that produces 15 gal- lons of sap with a sugar content of only 1° Brix yields only 1.3 pounds of sugar, or less than one- fifth gallon of sirup. The cost of producing the sirup from both tapholes is approximately the same. Trees producing sap with a sugar content of 10° Brix are especially profitable, as 15 gal- lons of sap from 1 taphole yields nearly P/4 gallons of sirup, or more than five times as much as the 2°-Brix sap. Trees that produce sap low in sugar (1° Brix or less) should be culled. Research is being conducted at the Universi- ties of Vermont and New Hampshire, at the Ohio Agricultural Experiment Station, and by the U.S. Forest Service on the propagation of maple trees from selected high-yielding trees (20, 32, 33, 3U, U5). This research should eventu- ally make it possible to set out maple orchards or roadside trees that will produce sap with a high sugar content. Use of a germicidal pellet to prevent prema- ture drying up of a taphole may increase sap yields as much as 50 percent. Since the results obtained by using the pellet are due to its germicidal action, it will not increase the sap crop in sugar groves where sanitary measures are already being practiced. Summary' (1) Consult your State extension forester, farm forester, and county agricultural agent and work with them to develop a management plan for your sugar grove. Aim for 160 tapholes per acre (160 trees 10 inches d.b.h. or 40 trees 25 inches d.b.h.). (2) Remove all defective, diseased, and weed trees. (3) Check the yield and sugar content (° Brix) of the sap from each tree. Cull trees that yield sap low in sugar (1° Brix). (4) For maximum sap yields use germicidal taphole pellets. TAPPING THE TREE The sap of the sugar maple, from which sirup and sugar are made, differs in composition from the circulatory sap of a growing tree. We know little concerning this sap, or sweet water as it is called in western Pennsylvania. Intensive study of maple sap at the University of Ver- mont (3U, 35, 57-59) should lead to a better understanding of its nature, function, and source, and of the factors responsible for sap flows. Sap will flow any time from late fall after the trees have lost their leaves until well into the spring, each time a period of below-freezing weather is followed by a period of warm MAPLE SIRUP PRODUCERS MANUAL weather. The sap will flow from a wound in the sapwood, whether the wound is from a cut, a hole bored in the tree, or a broken twig. Date of Tapping To establish a rule of thumb that can be used to set the date for tapping sugar maples is not a simple matter. The date should be early enough to assure collecting large early flows of sap (66). Michigan and New York provide sugarmakers with radio weather forecasts of the correct tapping dates (22). A similar service is being set up in other maple-producing States including Massachusetts, Vermont, and Wisconsin. Gen- erally, trees should not be tapped according to a calendar date. In 1953 when this practice was followed, many producers failed to collect the large early flow that resulted from an unsea- sonable, early warm spell. The danger of tap- ping too early is now largely eliminated through use of germicidal taphole pellets (17). When pellets are used, trees can be tapped several weeks ahead of the normal season. Selecting; Trees Selecting trees for tapping is of greatest im- portance and can be done at any time through- out the year. Trees that produce sap with a density of only 1° Brix, as determined with a sap hydrometer or refractometer, should be culled. Culling must be done during the period of sap flow (64). If time does not permit testing all the trees dur- ing one sap season, test as many as possible the first year and test the remaining trees during succeeding years. Trees selected for tapping should have a minimum diameter of 10 inches at 4V2 feet from the ground (d.b.h.) (fig. 10). A good rule (H, 6i) for determining the num- ber of tapholes that can safely be made in a single tree is as follows: Tapholes Diameter of tree, per tree,' inches number Less than 10 0 10 to 14 1 15 to 19 2 20 to 24 3 25 or more 4 ' Number of buckets. PN-4706 Figure 10. — Measuring the diameter of the tree to deter- mine the number of tapholes the tree will support. To undertap a tree reduces the potential size of the crop without any benefit to the tree. On the other hand, to overtap (fig. 11) may seri- ously damage the tree (72, 94). Once the trees have been measured, they should be marked so they will not have to be remeasured each season. This can be done by painting a numeral or a series of dots on the tree or by using paints of different colors, such as white for 1 taphole, yellow for 2 tapholes, etc. Boring Tapholes Tapholes are made by boring with either a ^/e- inch or a ''/le-inch fast-cutting wood bit. Al- though tapholes can be bored by hand with a carpenter's brace (fig. 12), this method is used only for very small operations. For large operations, a portable motor-driven drill not only speeds up the operation but also is far less fatiguing. These drills are made in two basic designs, one powered by a gasoline motor and the other by an electric motor. In one of the earlier models that is still popular (fig. 13), the gasoline motor is mounted on a packboard 10 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN^707 Figiire 11. — Overlapped tree (8 buckets on a 4-bucket tree). Note attempt to tap over large roots. PN-170K Figure 12. — Boring the taphole at convenient breast height. The hole is 6 inches from that bored the pre- vious season. and is connected to the drill by a flexible shaft. In other models, the drill is attached directly to the gasoline motor, which is held in the hand. The electric battery-powered drill (figs. 14 and 15) is newer than the gasoline-powered drill. It is light and free from vibration and is fast becoming popular. With either a gasoline- or an electric-powered drill, one man can drill holes as rapidly as a crew of two or three can set the spouts and hang the buckets or bags, or install the tubing. The hole is bored into the tree, preferably at a downward pitch of approximately 5 degrees. The downward pitch is especially desirable if germicidal pellets are used in the tapholes. The hole is bored 3 inches deep or until stained heartwood is reached. Studies at Michigan State University {57) have shown that a taphole 3 inches deep (fig. 16) produces up to 25 percent more sap than a taphole only 2 inches deep. The position of the first taphole is selected arbitrarily. The hole should be 2 or 3 feet above the ground or, if there is snow on the ground, as close as possible to this height. This low position is particularly well suited to the use of plastic tubing. The compass location of the hole is not important. Data obtained in New York (m) and in Michigan {16, 93, H, 96) have shovm that the total yield is essentially the same regardless of the compass location of the hole. However, the warm side of the tree is favored. Data also show that the height above ground level has little effect on yield. The best practice is to make the new taphole on successive years 6 to 8 inches from the previous year's taphole, working up the tree in a spiral pattern (fig. 17). With this procedure, the producer may tap his tree year after year in different quadrants and avoid striking an old taphole or dead tissue that has been hidden by new bark, either of which would result in a smaller flow and poorer qual- ity sap. When plastic tubing is used to collect sap, there is no minimal distance at which the taphole is located above the ground, and an even larger area of the tree becomes available for tapping. This permits a longer interval be- tween periods when a repeat tap has to be made in the same area of the tree. MAPLE SIRUP PRODUCERS MANUAL 11 PN-n09 Figure 13. — A gasoline-powered portable tapping drill with flexible shaft. PN-4711 The power tapping drill permits drilling the hole at different heights. rN-niii Figure H. — An electric battery-powered tapping drill. The time required for new bark to grow over a taphole depends on the health and vigor of the tree. It is not uncommon to find the hole nearly covered in a year (fig. 18). The hole itself remains open, but fungus growth (109) may occur in the new hole and stain the wood several inches above and below the hole and an inch or less to the side (figs. 19 and 20). Figure 16. — The taphole is bored into the tree 3 inches deep. Life of a Taphole A taphole should be usable from the time it is bored until the buds begin to swell and the sirup acquires an unpalatable or buddy flavor. In the past, the taphole often dried up within 3 or 4 weeks after the hole was bored. Drying up is caused by growth of micro-organisms in the 12 AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE taphole rather than by air drying of the wood tissue (13, 102, 103). When the microbial growth has reached a count of 1 million per cubic centimeter, sap will no longer flow from the hole, and it is said to be dried up (J7). In the past, a dried-up taphole was reamed to make it flow again; it was assumed that this procedure would remove the air-dried wood tis- sue. However, reaming was never successful. Research has shown that the reaming bit did not sterilize the hole. Reaming removed only a layer of the microbial deposit; the remaining bacteria kept on growing. Soon, sufficient num- bers were again produced to stop the flow of sap. The newly developed germicidal pellets have prevented premature drying of the tap- hole. PN-4714 Figure 18. — In a healthy, vigorously growing tree, the taphole will be completely covered with new wood and bark in 1 year. Figure 17: PN^ni:) -Tapholes arranged in a spiral about the tree. Figure 19. — A split section of a tapped maple log showing the longitudinal stain area above and below the tap- hole and the new growth of bark that has covered the outside end of the hole (left). Sanitizing Tapholes Germicidal Pellets A germicidal taphole pellet (fig. 21) has been developed at Michigan State University (17). If put into the taphole as soon as it is bored, the MAPLE SIRUP PRODUCERS MANUAL 13 PN-4716 Figure 20. — Cross section of a maple log showing stained area caused by fungus growth in old tapholes. The stains show the exact contour of the holes including the area entered by the screw of the bit, but do not indicate whether the holes lie above or below the plane of the cut. Note that the stain is confined to the width of the taphole, which indicates that the lateral damage to the tree is restricted to within one-half inch on each side of the hole. But damage may extend several inches above and below the hole, as shown in figure 19. pellet will keep the hole essentially sterile throughout the sap season (6 to 10 weeks) and therefore will permit flow of sap H, 5, 6) each time the weather is favorable. If large early flows of sap occur, a second pellet may be needed after 4 weeks. The active ingredient of the pellet is paraformaldehyde which, because of its germicidal effect and low solubility, makes it ideally suited to this use. Each pellet must contain a minimum of 200 milligrams of availa- ble formaldehyde at the time it is placed in the taphole. The function of the pellet is to contribute enough formaldehyde to the 1 to 5 milliliters of sap remaining in the taphole between flow periods to keep microbial growth to a minimum. When the sap is flowing, the short time it is in contact with the pellet permits only a trace of formaldehyde (less than 5 p.p.m.) to be dis- solved. This small amount of formaldehyde is removed from the boiling sap while it is being concentrated to sirup in the evaporator pan. The very low concentration of formaldehyde in the sap in the storage tanks will not maintain the sap in a sterile condition {133, 13 Jf). This is fortunate because it is sometimes desirable to culture the sap with specific micro-organisms or enzymes. Sap is cultured as one step in produc- ing high- flavored maple sirup; it is also cultured to destroy substances that are responsible for the buddy flavor in "buddy" sap («). Other germicides are under investigation (W, AD- Because of the very low residue of formalde- hyde in sirup, the U.S. Food and Drug Adminis- tration issued in February 1962 a regulation governing its use {130). However, under no circumstances should more than one paraformaldehyde pellet be placed in a taphole, nor should formaldehyde be added to the storage tanks. To do either might raise the concentration of formaldehyde in sap and contribute to a high concentration in the sirup. This would produce sirup containing more formaldehyde than specified in regula- tions of the U.S. Food and Drug Administration or of the State in which the sirup is made. PN-4717 Figure 21. — A germicidal pellet is inserted in a taphole immediately after the taphole has been drilled or after it has been flushed with hypochlorite solution. 14 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE While pellets were being developed and dur- ing the first 2 years they were used commer- cially (1962-63), records show that when weather was favorable to microbial growth in the tapholes, pellets doubled or trebled the yield of sap. Pellets are less effective when good sanitary practices are followed or when the entire maple season remains cool, since micro- bial growth is retarded under these conditions. Elimination of the cause of premature drying of the taphole permits tapping the tree before the sap season with the assurance that the first as well as the late run of sap will be obtained. Also, the cause of diminished flows throughout the season is eliminated. Both of these factors increase yields of high-quality sap and decrease the man-hours required to harvest sap (156). Germicidal pellets are especially desirable where plastic tubing is used to collect and transport sap in the woods. The pellets help to keep the pipeline (tubing) clean and sterile. Chlorinated Solutions In many sugar groves, chlorinated solutions are being used to control microbial growth in the taphole {133). The best procedure is to flush the taphole as soon as it is drilled with a solution consisting of 10 parts of a commercial hypochlorite solution (containing approxi- mately 5.25 percent of sodium hypochlorite) and 90 parts of water (fig. 22). Often where there is a week or more between sap runs and particularly if the nonrunning period is warm, the tapholes should be re- flushed with a solution of the same strength. Where this chlorination procedure has been practiced, a change to germicidal pellets may not increase sap yields. Summary' (1) Do not tap by the calendar. Follow your State's maple weather reports. (2) Tap before the sap-flow season. PN-4718 Figure 22. — Flushing the taphole with a 10-percent commercial hypochlorite solution. (3) Make 1 taphole in a tree 10 inches in diame- ter and 1 additional hole for each additional 5 inches of the tree's diameter. (4) Make the taphole with a ^'/s-inch or '/le-inch fast-cutting (special) wood bit. (5) Use a power tapper if the grove is large enough to justify the expense. (6) Bore the hole into the tree to a depth of 3 inches at a slight dov^Tiward pitch. (7) The location of the taphole in respect to compass position and roots is not important. (8) Space the holes at least 6 inches apart (circumference of tree) and in a spiral pat- tern. (9) Sanitize the taphole. Use 1 germicidal pellet per taphole. SPOUTS AND BUCKETS Sap Spouts The spout or spile has three important func- tions: (1) It conveys the sap from the taphole to a container; (2) it either connects the plastic tubing to the taphole or serves as a support on which to hang the sap bucket or bag; and (3) it keeps adventitious (wild or stray) bacteria from gaining access to the moist taphole, which should reduce infection if plastic tubing is used. MAPLE SIRUP PRODUCERS MANUAL 15 Over the years a large number of sap spouts have been designed and used, with special fea- tures claimed for each. The earliest spouts were hollow reeds, often a foot or more in length. Two reeds inserted in adjacent tapholes carried the sap to the same container (fig. 23). There are only a few basic differences in the design of the various sap spouts. Some have a large opening at the delivery end. Others have a hook to support the bucket and a hole for attaching the bucket cover. On others the bucket is sup- ported directly on the spout. All commercial spouts are satisfactory. A few spouts are shown in figure 24. Plastic spouts are used with plastic tubing and they have tubulations to which the tubing is attached. All spouts have a tapered shoulder so that when they are driven into position in the tap- PN-ni9 Figure 23.— Reed sap spouts, the forerunner of metal spouts. Figure 2U- — Wood and metal sap spouts. hole, they form a watertight seal with the bark and outer sapwood but leave a free space be- tween the sapwood and the spout. In setting the spout (fig. 25), care must be exercised not to split the tree at the top and bottom of the taphole. A split results in sap leakage and often all the sap from that hole is lost. To strike the bark a sharp blow damages the tree and often kills an area for several inches. Spouts should be cleaned at the end of each season. Metal spouts can be washed by tum- bling in a small concrete mixer containing a solution of a good detergent. Just before the spouts are taken into the sugar grove at the beginning of a sap season, they must be steri- lized by heating them in boiling water for 15 minutes or longer. The spouts are then put in a pail and covered with a chlorine solution con- taining 1 cup of a commercial bleach (5.25 per- cent of sodium hypochlorite) in 1 gallon of water. The pail of chlorine-wetted spouts is carried into the sugar grove. Rubber or rubber- 16 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Figure 25. — Setting the sap spout. coated canvas gloves must be worn to protect the hands from the strong bleach. Rain^uaixls Heavy rains often occur during the sap sea- son. Rainwater running down the tree picks up dirt and leaches tannins from the bark. Both the dirt and the tannins, if permitted to get into the sap bucket, lower the grade of the sirup produced. Most sap spouts are provided with "drip tips" to deflect runoff rainwater from the tree and prevent it from entering the bucket. In heavy downpours, drip tips are often inade- quate. Use of a simple, homemade rubber rain- guard (fig. 26) prevents the heaviest runoff rainwater from entering either a sap bucket or bag. To make a rainguard, cut a 2-inch square from a thin sheet of rubber, such as an old inner tube. With a leather punch, cut a ^/le-inch hole in the center of the square. Slip the rain- PN-4722 Figure 26. — Rubber rainguard prevents water from reaching the sap bucket. guard over the end of the spout near the tree and set it far enough forward so that when the spout is seated in the taphole there will be a free space of V4 to ^/s inch between the rubber guard and the bark of the tree. Sap Buckets and Bags Three types of containers have been used to collect the sap from the spout: (1) The wooden bucket; (2) the metal bucket; and (3) the plastic bag. The wooden bucket, because of its size and the care required to keep it watertight, has largely disappeared from use. Zinc-coated 15-quart buckets are the most commonly used metal buckets. Large 20-gallon galvanized cans that eliminate daily collection of sap are used in some "cold" sugar groves (high altitude, northern exposure). In a cold grove, the buckets often contain ice sap which retards microbial growth. The minute amount of zinc that is dissolved from the galvanized coating by the sap tends to reduce microbial growth, but the germicidal effect is nullified- if the zinc coating is overlayed with a deposit MAPLE SIRUP PRODUCERS MANUAL 17 from the sap (108). It can be made effective again by carefully removing the protective film overlaying the galvanized surface. The 20-gal- lon containers tend to reduce microbial growth more than do the smaller buckets (28). Lead- coated metal (terneplate) or lead-soldered buck- ets and buckets painted with lead paint should not be used because the lead may be dissolved by the sap, especially sap that has been allowed to ferment and sour. Sirup made from this sap may contain illegal amounts of lead. Aluminum buckets, which are being subsidized in Canada, tend to eliminate most objections to metal buckets. Every bucket should be provided with a cover to keep out rain and falling debris. Covers are of two general types: Those that are attached to the spout (fig. 27) and those that are clamped to the bucket (fig. 28). The plastic sap bag (fig. 29), a comparatively recent development, met with much favor, espe- cially before the development of plastic tubing. Some advantages of plastic bags are: (1) Be- cause of their small bulk and weight, they require minimum storage space, and they are easily transported to the woods and hung. (2) They have a self-cover that encloses the spout when the bag is in place, and thus limits access of micro-organisms to the open end of the spout and to the taphole. (.3) Emptying the sap is a one-handed operation (fig. 30). The bags need not be removed from the spout; they can be rotated on the spout. (4) Because they are transparent to sunlight radiation, which is le- thal to micro-organisms, they tend to keep the sap sterile (76). Sterile sap contributes to the production of high-quality sirup. Some disadvantages of plastic bags are: (1) They may open at seams, especially if the sap in a filled bag freezes. (2) They are difficult to empty when filled with ice. (3) The bag may be too small to hold a day's run. (4) The bags are subject to damage by rodents. (5) Washing and rinsing the bags may be difficult. PN-4723 Figure 27. — Sap bucket cover attached to the spout by means of a pin. With this type of cover, the bucket must be lifted free of the spout for emptying. PN-1724 Figure 28. — A clamp-on cover stays fixed to the bucket and is not easily blown off. With this type of cover, a bucket that is attached to the spout by means of a hook must be lifted free of the hook for emptying. However, a bucket that hangs on the spout by means of a large hole that will slip over the spout can be emptied by rotating the bucket and cover on the spout. 18 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN-4725 Figure 29. — Plastic sap bag: The amount of sap is easily seen and accumulations of sap, even from short runs over a long period of time, tend to remain sterile because ultraviolet rays of daylight are transmitted through the plastic. The bag has its own plastic cover. Since the spout is completely covered, it is free from contamination. Summary (1) Any commercially available spout is satis- factory. (2) Use only clean, sterile spouts. (3) Drive the spout into the taphole with a firm enough blow to seat it securely, but do not drive it so far as to split the bark and wood. PN-4726 Figure SO. — Emptying the plastic bag by rotating it on the sap spout makes it a one-handed operation. (4) Use a 2- X 2-inch rubber runoff rainguard on the spout. (5) Carry clean, sterile spouts wetted with a dilute, hypochlorite solution into the sugar grove. (6) Do not use buckets coated with lead paint or with temeplate. (7) Use containers large enough to hold a nor- mal day's run of sap. (8) Use only clean sap buckets or bags. (9) Use covers on all sap buckets or bags. COLLECTING THE SAP Collecting (gathering) sap by hand (fig. 31) is the most expensive and laborious of all maple sirupmaking operations and accounts for one- third or more of the cost of sirup production. When buckets or sap bags are used, much time can be saved if the trees to be serviced on both sides of a roadway bear a mark to distin- guish them from the trees to be serviced from an adjacent roadway. This prevents servicing the same tree from both roadways. Different colored paints can be used to mark the trees. Another timesaver requires punching a sec- ond hole in the sap bucket opposite the original hole, and painting a stripe from that hole to the bottom of the bucket. The buckets are hung first from one hole (for example, with the stripe away from the tree and plainly visible); after they are emptied, they are hung from the opposite hole. This makes it easy for the sap collector to tell whether a bucket has been emptied and keeps him from skipping full buck- ets as well as wasting time revisiting empty MAPLE SIRUP PRODUCERS MANUAL 19 Figure 31. — Collecting sap by hand is expensive. Usually two pails are used to collect the sap from the sap bags or buckets, and the sap is carried by hand to the collecting tanks. buckets. The only objection is that a bucket with holes on both sides holds less sap than a bucket with one hole because it hangs from the spout at an angle. Some producers empty the buckets by rotat- ing (spinning) them on the spout. This requires the use of a cover attached directly to the bucket and a spout on which the bucket is hung by means of a hole in the bucket. More sap may be spilled when buckets are emptied by spin- ning than when they are lifted free of the spout and tree. Spillage of sap when transferring it from bucket to gathering pail and from pail to collecting tank may account for an appreciable loss of the sap crop. Plastic tubing eliminates this loss (fig. 32). Sap must not remain in the buckets more than a few hours before it is collected. During short runs that produce too little sap to war- rant collecting, the buckets must be emptied, even though this is time consuming and expen- sive. The sap left standing in the bucket will ferment and spoil and will spoil other sap to which it is added in the collecting or storage tanks. PN^728 PN^7 Figure 32. — No labor is required when tubing is used to collect sap. Collecting Tanks Collecting tanks vary in size according to the needs of the sugar grove. The tanks usually are provided with a strainer, baffled to prevent loss of sap by splashing, and a drainpipe. The method of hauling the tank is governed by conditions in the sugar grove. The tank can be mounted on any of several types of carrier, including stoneboat or skids, 2-wheel trailer, high wheeled wagon gear, and underslung rub- ber-tired, 2-wheel trailer (fig. 33). High-mounted tanks should be avoided be- cause of the labor required to lift the sap (fig. 34). Usually an additional worker is needed. A rig of excellent design has a low-mounted sump tank and a self-contained, power-driven pump to lift the sap up to the large tank (figs. 35-38). A new type of collecting tank being widely adopted employs vacuum (suction) for filling. Tanks to be filled by suction must be airtight and structurally strong enough to withstand an external pressure of 15 pounds per square inch (1 atmosphere). Tanks larger than 300 gallons require internal bracing. The vacuum can be obtained by a separate pump or by connecting a line from the manifold of the truck or tractor engine (fig. 39). To prevent sap from entering the engine manifold, a float check valve is mounted on the tank and the vacuum line is attached to this (fig. 40). The check valve is 20 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE / \ w^hB^^y^^HHE^^^HuA^lBflS PN-4729 Figure SS. — Collecting tank mounted on a truck body. This type of assembly does not require special rigs, but an additional man is needed to empty the pails into the tank. PN-n3n Figure Si. — Additional labor is required to lift sap to a tank mounted on a trailer. similar to those used in milking machines that prevent milk from entering the pump. If sap reaches the motor, it causes serious damage. A 1,000-gallon tank can be emptied and put back into operation in only a few minutes. The suction line is a 1-inch hose, which will pick up 30 gallons of sap per minute. Instead of a slow- acting valve in the suction line, a tapered plug is used in the pickup end of the hose. This plug is removed just before the hose is submerged in the sap in the tank or bucket to be emptied. PN-4731 Figure S5. — For large operations or for collection from roadside trees extending along several miles of roads, the large tank trailer is desirable. If a closed tank and an engine manifold vacuum system is not available, a pump-and- vacuum system can be used (2). In this novel system, an air-cooled gasoline motor operates a pump which, in turn, creates a vacuum in a small tank. The sap is discharged into a conven- tional collecting tank. Regardless of how the vacuum in the suction (sap pickup) line is developed, this method of collecting sap is efficient and fast, causes a minimum of loss due to spillage, and can be used for collecting sap from the conventional metal bucket, from the large 20-gaIlon con- tainer, and from small and large storage tanks. Whether or not the collecting tank has a vac- uum line pickup, the tank must be as large as roads and other conditions will permit. The smaller the tank, the greater the number of costly trips that must be made. Pipelines Metal pipelines have been used in the maple sugar grove for 50 years or more. The early metal pipe carried the sap over almost impassa- ble terrain, from one sugar grove to another or to the evaporator house (figs. 41 and 42). Metal or wooden troughs have also been used as "pipelines." All these pipelines, whether metal pipe or metal or wooden troughs, had one serious draw- MAPLE SIRUP PRODUCERS MANUAL Figure 36. — Sap is easily poured from buckets into a low sump tank, from which it is pumped into the large tank. PN^733 Figure 37. — The sap is lifted from the sump by means of a pump. Power for the pump can be supplied by a takeoff from the tractor or truck engine or by a small gasoline PN-4734 Figure 38. — Vacuum lines operated by a vacuum pump can be used to empty buckets and small containers in the woods or at the roadside. PN-4735 Figure 39. — The vacuum is obtained from the manifold of the truck engine. 22 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Figure 40. — Float valve assembly and vacuum (suction) line. back; they had to be installed with great care so that there would be no sags in the line. Sags in pipes permitted the sap to lie there and, when a freeze occurred, the ice formed would often burst the pipe. Sags in troughs permitted the sap to overflow. In addition, metal pipe was hard to clean. Since metal pipes are opaque, there is no simple means to determine when they are clean. Nevertheless, the saving in time and labor made possible by these earlier pipe- line systems justified their use. Suimnai*y (1) Collecting sap by hand and hauling it is the most expensive operation of sirupmaking. Examine all steps and introduce laborsav- ing methods where possible. PN^737 Figure il. — Use of pipelines to carry sap over impassable areas saves time. With a lateral system of dumping stations, collecting tanks can be eliminated in some locations. The pipeline also makes accessible some sugar groves that would be impossible to reach by tractor or truck. PN^738 Figure 42.— When the sugar grove is at a higher elevation than the evaporator house, the pipeline carries sap from dumping stations at the edge of the sugar grove to the evaporator house. This eliminates long and costly hauls of sap. (2) Wherever possible, use pipelines to trans- port the sap. Do not collect spoiled sap. Do not allow small runs of sap to remain in the buckets. Do not spill sap when pouring it into collect- ing pails and tanks. This can account for a 10-percent loss. (5) Use as large a collecting tank as possible to avoid repeated hauls. (6) Use a -pump or vacuum to fill the tank. (7) When vacuum is used, be sure the tank is internally braced to withstand the high ex- ternal pressures. (8) Keep all equipment sanitary at all times. (3) (4) MAPLE SIRUP PRODUCERS MANUAL PLASTIC TUBING 23 With the advent of plastic tubing, most of the objections associated with metal pipes have been overcome. Not only can plastic tubing be used for collecting and transporting the sap, but also it is cheaper to install, it has greater flexibility and elasticity, and it is easy to keep clean. Wide acceptance of plastic tubing by maple producers (.38) has been a major factor in modernizing the 300-year-old maple industry. Use of plastic tubing has practically elimi- nated the hard, unattractive labor of collecting sap and has lowered the cost of sirupmaking as much as 40 percent. No longer is it necessaiy to construct expensive roadways through the woods to support heavy tanks of sap and to open these roads after heavy snows (fig. 43). Tapping need not be delayed until the sap season has arrived. Large crews do not have to be hurriedly assembled to tap the trees and hang the buckets. Instead, the lightweight plas- tic tubing can be carried by hand through the woods when convenient. Some setbacks were encountered when plas- tic tubing was first introduced. Since it had been emphasized that sap issues from the tree under high pressure (,39), systems for installing the pipelines were patterned after those used for high-pressure waterlines. It was anticipated that enough pressure was developed by the tree to force the sap through the pipelines, but this was not true. The sap leaks from the tissues of the tree under a wide range of pres- sures, from very low (almost immeasurable) to as much as 40 pounds per square inch. The pressure is affected by many factors, among which are the temperatures of the air, tree bark, and soil. In many runs, and often throughout most of a run, sap leaks from the tree under very low pressure. Thus, only a slight obstruction in a pipeline provides suffi- cient back pressure (resistance to flow) to equal or exceed the pressure at which the sap is being exuded from the tree. Hence, sap flow is pre- vented. Causes for back pressures (obstructions) in the line are (1) gas (vapor) locks resulting from pockets of gas exuded from the tree along with the sap (8) or from air pockets that result from air that has leaked into the tubing around the different connections, especially at the spouts (through the vent tubes); (2) low places in the line where pockets of sap collect, and (3) ice plugs of frozen sap. Of these three causes, gaslocks are most frequent and may cause enough back pressure to support a 5-foot col- umn of sap. However, gaslocks can be kept to a minimum by careful installation and by provid- ing vents to free the trapped gases or air. The effect of ice in the pipelines is a contro- versial subject. Many believe that by the time the air temperature has risen sufficiently to cause sap to flow from the tree, the tubing will have warmed sufficiently to partly melt the ice and allow passage of the sap. Others believe that the elasticity of the tubing will permit the sap to pass by the ice plug. This is unlikely. Still others believe that tubing laid directly on the ground, whether snow covered or not, will ab- sorb enough latent heat from the earth to melt the ice in the tubing before any appreciable flow of sap occurs. Ice in tubing installed on the ground often melts before ice in tubing sus- pended in the air. (This can be observed when the two systems are installed in the same sugar grove.) There is almost complete agreement that ice in tubing layered between two falls of snow melts very slowly because of the insulat- ing effect of the snow. The tubing must be pulled up out of the snow before the ice will PN-4739 Figure AS. — Tubing can be used for a small group of trees in an inaccessible area or for roadside trees. 24 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE melt and unblock the lines; this is not easy to do when the lines are suspended. Since maple sap is not exuded from trees at all times under high pressure, the best method for installing the tubing is one patterned after that used in gravity-flow waste-disposal sys- tems. These systems are installed with a con- tinuous, even though slight, pitch of both the feeder lines Qaterals) and main lines toward the exit end. Main or trunk lines nuist be of suffi- cient diameter so that they are never over- loaded. Vents must be installed at all high points to prevent gaslocks, and a vent must be installed at each spout. One of the outstanding features of the plastic pipeline is the "closed" system — transparent to daylight which minimizes microbial infections and keeps the sap clean and free of foreign matter (2S, 31). However, infection can and does occur; therefore, sanitary precautions must be observed in installing and maintaining the sys- tem. The immediate effects of infection are deteri- oration and spoilage of the sap. Since infection can be translocated by the moving sap, two or more tapholes must not be connected in series. This might spread infection from one taphole to another (31 ) and prematurely stop sap flow. For the same reason, tubing that connects the tap- hole to either lateral or main lines must be installed with enough elevation between the lateral line and the taphole to drain the sap away from the taphole freely and completely during periods of flow and to provide sufficient hydrostatic pressure to insure flow in the main lines laid on level ground. Installation of flexible plastic tubing Qateral or main lines) suspended in the air above the ground, free of sags between points of support and with a continuous pitch, would be an even greater problem than installation of iron pipe. A suspension cable would be required. It would be stretched from tree to tree above the tubing; the tubing would be suspended from it and held in a "straight" course by hangers of different lengths. In practice, however, sags cannot be prevented because fluctuating air tempera- tures expand and contract the tubing and cable and because the tubing between the hangers is not rigid. Also, locating these lateral and main lines so that- all tapholes will be a short but fixed distance above the main lines U8-50) would increase the difficulty of installation be- cause numerous main lines and short lengths of lateral lines would be required. This system is ideal for small installations involving one or only a few trees. Do not connect tapholes in series except on individual trees. To do so may spread microbial infection and stop flow of sap prematurely. In expanding this system to a large opera- tion, the costs of initial installation, takedown, and reassembly might be excessive. The system does, however, eliminate the need of taphole vents, since the short length of the dropline is attached to main lines that are not completely filled with sap and so will not air-lock. A properly installed pipeline system drains itself. If sags occur in either ground- or aerial-sup- ported systems, pockets of sap will form. These pockets cause buildup of back pressures, reduce flows, are sites of microbial infection, and form ice plugs on freezing. Installing Tubing There are many methods for installing plastic tubing (68, 70). The following method (152) is economical of materials and labor, minimizes spread of microbial infection, and tends to elimi- nate gaslocks and other obstructions that build up back pressures in the lines. It provides a simple, inexpensive, and satisfactory means for installing, taking down, washing, sanitizing, and reinstalling plastic tubing. Equipment Droplines. — Complete assemblies of 5-foot lengths (for level land use 6- to 7-foot lengths) of ^/le-inch inside diameter (I.D.) tubing with a tee at one end and a sap spout at the other. The spout has a vent tube attached. Vent tubes are U-shaped Vie-inch I.D. tubes formed with a short piece of wire; they are from 6 to 12 inches long and are attached to the vent tubulation of the spout (chart 3). The U-shape tends to keep micro-organisms out of the system. Lateral Lines. — Lateral lines, made of ^/le- inch I.D. tubing, connect the droplines to the main lines. They are laid on the ground. Main Lines. — Main lines vary in size from V2 to IV2 inches- I.D. MAPLE SIRUP PRODUCERS MANUAL 25 ALUMINUM WIRE VENT TUBE ^ ID. TUBING 16 V Chart 5.— Vent tube and drop line assembly. Spouts. — Spouts have two tubulations, one for discharging the sap and the other for vent- ing gases. Tees and Connectors. — Plastic tees, connect- ors, and other fittings of appropriate size are required for connecting droplines, lateral lines, and main lines. Hypochlorite Solution. — A commercial bleach containing 5 percent of sodium hypochlorite is diluted with water at the rate of 1 gallon of bleach to 19 gallons of water. Germicidal Pellets. — One germicidal pellet is required for each taphole. Some producers find it desirable to flush all new tubing with a stream of pure water for 10 to 15 minutes before putting it into use. This removes any soluble material in the tubing, including that which might produce an off- flavor. Droplines can be completely assembled at odd hours before the sap-flow season. They are assembled before they are installed in the sugar grove and are not disassembled until they need to be replaced. A complete dropline is used for each taphole on each tree. To install the lateral and main-line tubing so that it will have the desired pitch without sags, lay out the route it should follow before the sap season when the ground is bare and the trees along the route have been blazed. Painting the trees with vertical lines (blaze marks) will show the number of tapholes to be made per tree. The paint can be applied in a fine stream from a pressure paint can. Where the slope of the ground is not too steep, it is recommended that a tractor with scraper blade be run over the route to level it. A short time before the sap season, the trees should be tapped and the tubing installed. Al- though this can be done by one man, a three- man team is more efficient. Not more than 25 droplines (tapholes) per lateral line should be installed. V/f Li, Beginning at a location farthest from the storage tank and where two lateral lines con- verge, main lines should be laid in the most direct route to the storage tank (figs. 44-49). Low places should be avoided if possible. The first length of the main line should be V2-inch LD. The size should be increased as the quan- tity of sap entering it increases. On level ground, a V2-inch main line will carry the sap from 75 tapholes. Where two or more V2-inch I.D. main lines converge, they should be at- tached to ^/4-inch or 1-inch main lines. These, in turn, are connected to still larger main lines as the number of converging lines increases. In many sugar groves only V2-inch LD. main lines are required. There is no absolute rule regarding size and length of main lines except that they must be large enough in diameter to prevent buildup of back pressure. Pressure buildup can easily be seen by installing 6- foot lengths of ^/is-inch vent tubes in a vertical position at the junction points. If sap rises in the vent tubes, the main line is too small. The carrying capacity of a V2- inch main line equals three to four ^/le-inch 26 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE lateral lines, and a ^/4-inch main line equals two V2-inch lateral lines. When a graded course having a uniform downward pitch to the tank lines is impossible because of the contour of the land, the main lines should be suspended from overhead guy wires or cables. Suspended installation is espe- cially suited for long runs of rnain lines over very rough, rocky land, gullies, ravines, and valleys. A properly installed main line will drain itself. Tapping nnd Droplines If trees are tapped and droplines are installed by a three-man team, the first man locates the position for the taphole and bores the hole. He sanitizes the bored hole either by syringing it with the hypochlorite solution or by inserting a germicidal pellet. The second man carries the dropline assembly and attaches it to each tap- hole by driving the spout firmly into the tap- hole. The third man furnishes droplines, hy- pochlorite solution, and other supplies to the first two men. PN-4-41 unction of several main lines with surge tank and vent. PN-4-40 Figure H- — Main line used to transport sap across inaccessible area. Figure J,6. — Main lines transport sap to storage tank at the evaporator house. MAPLE SIRUP PRODUCERS MANUAL 27 PN-4743 Figure U7. — Main line to roadside tank for pickup. Lateral Lines Coils of ^/le-inch LD. tubing are taken to the Figure j,><. starting point of installation in the sugar grove, usually the storage tank at the roadside or at the evaporator house. The laterals are laid out and connected by a second three-man team. The leadman of the team carries the coil of tubing. One of the other men holds the end of the tubing. The leadman lays the tubing to the first tree tapped. The line should be kept free of loops and should lie flat on the gi-ound. The tubing is gently pulled to straighten it out and the desired length is then cut from the coil. One of the other two men holds the cut end of the coiled tubing, and the leadman advances to the second tree, laying out the tubing as he goes. The second and third men alternate in the following tasks: Holding the tubing while it is being laid out; disinfecting the ends of the tubing, tees, and connectors; and connecting the laterals to the tees of the droplines. Where there are multiple drops (tapholes) on one tree, they are connected with 1-foot pieces of */ie-inch LD. tubing. Laying tubing in shaded areas should be avoided. All connections and droplines to later- Figure 1,9. f'N-n4j -Droplines are installed before ground lines are laid out. PN-4746 -The leadman carries the coil of tubing. 28 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE als should be on the southern side of the tree to favor early thawing of any ice formed in the joints (figs. 50 and 51). After the tubing has been installed, the en- tire system must be checked to insure' that all connections have been properly made. Inspec- tion tours should be repeated throughout the sap-flow season to check for le^ks and sepa- rated joints. Inspections are necessary if the tubing was installed over deep snow that melts during the sap season or if new fallg of snow cover the tubing. Takinjj Down Tubing Tubing must be taken down not later than 1 week after the last run, or after the trees begin to bud. To delay permits growth of micro-orga- nisms and makes washing and sanitizing more difficult. During the sap-flow season, tempera- tures are usually cool enough so that the rate of germination of any micro-organisms in the tubing is slower than their death rate caused by the transmission of ultraviolet radiation of sunlight through the tubing. But, as the season progresses beyond the budding period, the PN-47 4(1 Figure 50. — Droplines are connected to laterals. PN-4747 Figure 51. — Several laterals are joined to the main line with tees or the newly developed collector. warmer weather causes the growth rate to greatly exceed the death rate of the organisms, and abundant growth occurs. Therefore, taking the tubing down immediately after the end of the season makes the cleaning operation easier. The process for taking the tubing down is merely a reversal of that described for its in- stallation. Like the installation, this process can be a one-man operation; but it is more efficient when done by two 2-man teams. The leadman of the first team at each tapped tree disconnects the droplines from the laterals and the foot-long connectors, which he collects. The second man pulls the spouts from the tree and collects the dropline assembly. Disconnect- ing lateral lines, short connectors, and drop- lines, and tying tubing bundles are shown in figures 52-56. MAPLE SIRUP PRODUCERS MANUAL 29 When 25 droplines have been collected, they are tied into bundles, with the tee ends flush. Since all droplines are alike, no labeling is needed. Figure 52.— Taking down droplines. Figure 53. — Taking up lateral lines. Figure .54.— Tying and labeling bundles of lateral lines. The second team collects, bundles, and tags the disconnected lateral lines. The leadman collects the tubing. Beginning at the first tapped tree, he picks up the end of the tubing that extends from the main line or storage tank and pulls the tube to the second tree. There he picks up the end of the tube e.xtending between the first two trees and places the end flush with the end of the first tube. Then he pulls the two lengths of tubing to the third tree and repeats the process until a handful of tubing (20 to 25 pieces) has been collected. Smaller lots may be obtained from an isolated section of the sugar grove. When a handful of tubing has been collected, it is left at the tree where the last piece was collected. Another member of the team ties the flush ends together into a bundle and attaches a label showing the general area of the sugar grove where it was installed. The bundle of tubing is then tied into a coil approximately 2 feet in diameter for easy handling. This system of installing and dismantling the tubing not only is simple but makes washing and sanitizing of the tubing easy. \^a!*liiii<; and .Saiiilizin^ Tiil»iii<£ At the end of the maple season most of the interior of the tubing is either wet or moist with sap. With the warmer weather at that time. 30 AGRICULTURE HANDBOOK 134. U.S. DEPT. OF AGRICULTURE Figure 55. PN-47.'->l Coiling lateral lines for ease of handling. Figure 56. — Load of tubing to be taken to evaporator house for cleaning and storage. temperatures are favorable to microbial prrowth (yeasts, molds, and bacteria). However, if the sap in the tubing: were sterile, either because of excellent sanitary practices or because of the sterilizing effect of sunlight, no subsequent gi'owth would occur. But this seldom, if ever, happens. Excessive microbial growth usually occurs, especially if higher temperatures follow takedown of the tubing. Once gi'owth occurs, it becomes increasingly difficult to clean the tub- ing. Therefore, the tubing should be washed within a few hours after its takedown, and if that is not possible, within 1 or 2 days. Tubing in which microbial gi'owth is excessive must be cleaned by more elaborate methods. Etiiiifniiriil The following equipment is requii'ed for washing the tubing: (1) A tank to hold the hypochlorite solution. This can be a 55-gallon drum or a stock-water- ing tank of approximately 200-gallon capacity. (2) A gear-pump that will deliver at least 50 gallons per hour at 10 to 15 pounds' pressure. A bypass arrangement on the pump provides flex- ibility of operation. The pump is attached to the drain valve of the tank and is equipped with a 15-foot length of hose provided with a tapered nozzle. (3) Wash or sanitizing solntioti consisting of a 10-percent solution of a commercial liquid bleach (which contains approximately 5 percent of sodium hypochlorite); 20 gallons should be used with 180 gallons of water. ii) Rubber gloves to protect the hands against the caustic action of the sanitizing solution. MAPLE SIRUP PRODUCERS MANUAL 31 W ashing l.H Figure 60. — The tubes are laid out on an incline or over a roof to drain. Here, 12 miles of tubing is being dried. Extremely dirty tubing or tubing; with an ex- cessive amount of microbial growth should be thoroughly cleaned (Hi ). For storage, several bundles of tubing from the same area of the sugar grove may be wound and tied in the same bundle. The coils of PN^757 Figure 61. — The tubing is coiled on a homemade reel, tied into bundles for storage. tubing are stored in a clean, dark, cool place that is free of rodents. Large metal drums or tanks with 'Vinch-mesh hardware cloth covers make ideal, rodent-free storage containers. A bundle of droplines held by both ends is lowered slowly and perpendicularly, tee end MAPLE SIRUP PRODUCERS MANUAL 33 first, into the tank of hypochlorite solution to displace the air and to completely fill the tubing and fittinfa:s (tees, sjwuts, and vent) with solu- tion (fig. 62). Without releasing the bundle, it is lifted out of the solution and held in a vertical position for a few moments to drain. The ends are then reversed and the bundle is again lowered into the solution. After the second filling the bundle of droplines is left in the tank to soak for 2 hours. After the soaking period, it is lifted free of the solution and held in a vertical position for a few seconds to permit most of the hypochlorite solution to drain back into the tank. The bundle is then hung by the cord ties at the spout end for 2 weeks (fig. 63). After draining, the bundle of droplines is taken down and stored in the same manner as the lateral lines. Washitif! Main Lines The coils of main lines are washed, drained, and stored in exactly the same manner as the lateral lines. A larger nozzle is used to fill and flush the tubing with the hypochlorite solution. Reinstalling Tubing; The operation of reinstalling the tubing in the sugar grove proves the merit of this system. This operation is carried out in practically the same manner as that of the initial installation. Main Lines The cut, clean, large-diameter tubes are laid out in the sugar grove in the same manner as in the initial installation. Droplines and Lateral Lines Two 3-man teams are used to reinstall drop- lines and lateral lines. The first team drills and sanitizes the tapholes and inserts the germici- dal pellets, and installs the dropline assemblies that have been kept intact in convenient bun- dles. PN-47SK Figure 62. — A bundle uf dicjijlines is lowered slowly and jierpendicularly into the wash solution. PN-n59 Figure 63. — The drained droplines are hung in a vertical position to dry. 34 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE The second team lays out and connects the lateral and main lines. The coiled bundles of lines are sorted and the one with the label for the sugar grove area where the work is to begin is selected. The coil is cut apart, and the lead- man of the team, holding a bundle by the tied flush ends, pulls it to the first tapped tree, following- the blaze marks of the preceding year. Since each bundle contains tubing of different lengths, the second man (who is at the starting point at that time) selects the tube that matches the distance from the starting point to the first tree and pulls it from the bundle. Both men now advance. The leadman proceeds to the second tree and the second man to the first tree, where he again selects a length of tubing that matches the distance between the two trees. He connects the lateral lines with the tees of the droplines. This procedure is repeated until the entire grove has been reassembled with the droplines and lateral lines. siimniarv' Plastic tubing can be used for the full opera- tion of sap collection and transportation or it can be used to perform parts of these opera- tions. (1) Install plastic tubing as a drainage system with proper vents and adequate size tubing so as not to restrict sap flow in tubes. (2) Do not connect tapholes in series, except possibly those on individual trees. (3) Lay the tubing on the ground or suspend it. Avoid any sags in the lines, and vent these whenever they occur. Installiufi Tubinn (1) Tubing is ground-supported lateral and main lines. (2) Each taphole is connected to the lateral line by a dropline consisting of a spout, vent, and 5-foot length of ^/le-inch tubing, and a tee connector, preassembled. (3) Lateral lines are ^/le-inch tubing cut to fit between different trees. (4) Make connections of lateral lines and drop- lines on warm side of trees. (5) Lay the lateral lines along a route of con- stant pitch free of sags, previously laid out. (6) A 3-man team lays out the lateral line most efficiently. (7) The number of droplines connected to one ^/i6-inch lateral line will depend on (a) the flow of sap per taphole and (b) the pitch of the lateral line. Do not connect more than 25 tapholes per lateral line. (8) A V2-inch main line will cari-y sap from 75 tapholes (3 laterals). (9) Increase the size of the main lines so that they are never overloaded. Failure to do so will cause back pressure and loss of sap. (10) Periodic inspection of the tubing is re- quired for leaks. Taking Doivn Tubing (1) Take the tubing down as soon as possible — never later than 1 week after last run. (2) Remove all droplines intact, and tie in a bundle. (3) Keep 1-foot connectors separate. (4) Collect lateral lines, keeping the lead ends flush in the hand-held bundle. (5) Coil and tie for ease of handling. (6) Label the bundle at flush ends for the area of woods where installed. Washing and Sanitizing (1) Wash all tubing in a 5-percent hypochlorite (bleach) solution. (2) Submerge and soak all tubing and fittings in hypochlorite solution for at least 2 hours. (3) Flush out all tubing as per preceding in- structions. (4) Keep flush ends of tubing tied in bundle at all times. (5) Open coiled tubing after washing. (6) Lay tubing on incline to drain. (7) Hang droplines in vertical position. (8) Recoil droplines and mains for storage. (9) Store in dark, dry, rodent-free area. Rfinstalling Tubing (1) Follow the same procedure as initial instal- lation: (a) Install droplines. (b) Connect droplines. (c) Lay out lateral lines and connect to droplines. (d) Connect lateral lines to main lines. (2) Lateral lines are laid out according to the scheme outlined in text. MAPLE SIRUP PRODUCERS MANUAL VACUUM SYSTEMS 35 The most recent development in collecting sap has been the use of vacuum to increase taphole flow and facilitate sap transportation in plastic tubing and pipeline systems (7, 1,7, 105). To utilize vacuum, an unvented or closed tub- ing system must be used. The vacuum may be created by the flow^ of the sap through the tubing due to gravity (natural vacuum) or by the use of a pump (pumped vacuum). The best vacuum system will depend on the individual characteristics of terrain and tree stand for each sugar bush. Where an adequate natural slope exists, natural vacuum can produce siza- ble increases in the yield of sap. The details of installing such a system are described by Mor- row (73). Gains in sap production are generally directly proportional to the amount of vacuum in the system, whether produced by natural flow or by a pump. As there are many areas in the North American maple belt where the slope of the land is not sufficient for an effective natural vacuum, artificial vacuum systems have been developed. Several agencies have done research on pumping systems (19, 106). A review of the different types of units that can be assembled was presented at the Eighth Conference on Maple Products (UU). It has been well substantiated that vacuum markedly increases sap yield. However, the re- ports on the use of vacuum emphasize the relative complexity of the equipment systems. Those wishing to incorporate vacuum, either natural or pumped, into their sap collection should obtain assistance from someone thor- oughly experienced with these systems. County agricultural agents in the maple sirup-produc- ing areas can recommend sources of expert advice on using vacuum and on installing the equipment needed in a sap-collection system. STORAGE TANKS Storage tanks serve the dual purpose of pro- viding supplies of sap to the evaporator and of storing sap until it can be processed or hauled to an evaporator plant. Tanks supplying either a farm evaporator or a central evaporator plant must hold enough sap for at least 2 days' operation. Tanks used as pickup stations must be large enough to hold the maximum daily sap production of the sugar grove or of the area they serve. Pickup tanks used to haul sap from the sugar grove or to deliver sap to the evapo- rator house must be as large as possible to reduce the cost of haulage. Wherever possible, locate the tanks so that they can be filled and emptied by gravity (figs. 64 and 65). When this is not possible, motorized pumps (electric or gas engine) can be used. The tanks should be located in a cool place (fig. 66) and not inside the warm evaporator house, since warm sap favors microbial gi'owth. The tanks should be covered to keep out foreign material, and the cover should be clear plastic or some other transparent material that will transmit the short ultraviolet rays of daylight (100). This type of installation is especially suited for roadside storage. If abovegTound tanks are not emptied fre- quently, they should be insulated to prevent the stored sap from freezing. Underground tanks with opaque covers, although less likely to freeze, are difficult to irradiate with ultravi- olet light (fig. 67). When the covers of under- ground tanks are not transparent to the ultra- violet irradiation, germicidal lamps must be installed at the top of the tanks to illuminate the entire surface of the sap. Underground tanks will usually keep the sap at a more even (and perhaps at a slightly lower) temperature than will aboveground tanks. But since many of the bacteria that infect sap gi-ow well at low temperatures, underground storage will not prevent microbial fermentation and spoilage of sap. Even lowering the temperature of the sap by adding ice will not prevent this. Large storage tanks such as those at the evaporator house should also be provided with germicidal, ultraviolet lamps to prevent micro- bial gi-ovd,h. These lamps should be mounted at the top of the tanks above the liquid level and arranged so that they will illuminate as much of the surface of sap as jwssible. Directions for making an inexpensive ultraviolet-irradiation 36 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE }'N-4760 Figure 61,. — The plastic-covered roadside tank should be large enough to hold a maximum daily run and should be located so as to permit gravity filling of the collecting tank. Figure 65. — This receiving tank is mounted at the road- side. Sap is pumped from it to the evaporator storage tank. Figure 66.— This small evaporator storage tank, mounted in the shade, is e.xposed to daylight and covered with transparent plastic. MAPLE SIRUP PRODUCERS MANUAL 37 unit for pasteurizing flowing sap are available (AS). CAUTION € are mil St be taken nevt »r to exp ose the eyes to ultraviolet lamps. Lamps must be turn es. en ^^^...^^^ 0 1 1 l" — \ 30 60 90 TIME (MINUTES) 120 150 Chart 7. — The average time (time required to remove 50 percent of the water) that any lot of sap remains in the sap pan (see dotted lines) is slightly less than 30 minutes. The time can be shortened or lengthened by using sap of lower or higher solids concentration (° Brix), by varying the depth of sap in the evaporator, and by varying the intensity of the heat. MAPLE SIRUP PRODUCERS MANUAL 47 60 90 120 150 TIME ( MINUTES) Chart 8. — The average time (time required to remove 50 percent of the water) that any lot of sap remains in the sirup or front pan (see dotted Hnes) is a little more than 60 minutes. The time in this pan can also be shortened or lengthened by changing the Brix value of the sap entering the sirup pan, by varying the depth of the sap, and by varying the intensity of the heat. must be adjusted to keep the sap proportion- ately deeper. A change in the Brix value of the sap in the supply tank requires a readjustment of the float of the intake valve. Changing to sap with a higher Brix value without readjustment may result in a burned pan. Rates of Evaporation The solids concentration of the sap is about doubled before it leaves the sap pan, that is, nearly 50 percent of the water that is to be removed has been evaporated {111, 140). By the time the sap reaches a concentration of only 19° Brix, 90 percent of this water has been evapo- rated. The changes in the concentration of a typical sap (2.5° Brix) during evaporation are given in table 4. A two-section evaporator with three channels in the sap (flue) pan and four in the sirup (front) pan and the points at which the concentration was measured (table 4) are shown in chart 9. To make 1 gallon of standard-density sirup from this sap required , or 34.4 gallons of 2.5 sap; 33.4 gallons of water had to be evaporated. The solids concentration of the sap was doubled (from 2.5° to 5.0° Brix) in the sap pan. This re- moved 17.3 gallons of water, or more than 52 Table 4. — Changes in the solids concentration of sap (° Brix) and water evaporated in a simulated evaporator, for each gallon of sirup produced Solids concen- tration Water ev aporatec Section of evaporator Per section Total of sap Gal- Per- Gal- Per- "Brix lons cent lons cent Original sap 2.5 Sap pan: First section ___ . 3.0 5.77 17.35 5.77 17.35 Second section _ _ 3.7 5.40 16.24 11.17 33.59 Third section . 5.0 6.16 18.53 17.33 52.12 Sirup pan: Fourth section , _ 8.0 6.45 19.40 23.78 71.52 Fifth section ___ _ 19.0 6.26 18.83 30.04 90.35 Sixth section _ 42.0 2.48 7.46 32.52 97.81 Seventh section 54.0 .45 1.35 32.97 99.16 Finished sirup - _ - 65.5 .28 .84 33.25 100.00 ' Percentage of sugar. - When this experiment was conducted, the Brix of standard sirup was 65.5°. ^S\ Chart 9. — Top view of a simulated maple sap evaporator having 3 channels in the sap pan and 4 channels in the sirup pan. Arrow shows direction of sap flow. The solid circles show the location of sap of different solids concentrations (° Brix), as indicated in table 4. 48 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE percent of the 33.4 p:allons of water that had to be removed to make 1 gallon of sirup. By the time the solids had increased to only 19° Brix, 90 percent of the water had been removed, and the sap had progressed only halfway through the sirup pan. Thus, the remaining 10 percent of the water was removed in the last half of the sirup pan. This shows that most of thf water is evapo- rated while the solids are at sufficiently low con- centrations to have little effect on the color of the sirup. It also shows that sap must be kept moving forward through the pan as it ap- proaches sirup concentration, so that it can be removed from the evaporator as quickly as pos- sible. This also explains why adding one or more sap (flue) pans in a series does not increase evaporation time but does increase evaporation rate and capacity. Lengthening the evaporator system by increasing the number of feet that the sap must travel through the different chan- nels makes use of the engineering rule that evaporation (heat transfer) increases as the rate at which the liquid moves over a heated surface increases. Thus, lengthening the evapo- rator by using supplementary flue pans will not increase holdup time; it actually decreases it. Therefore, the percentage of solids (weight-vol- ume) of the sirup divided by the Brix value of the sap equals the number of gallons of sap required to produce 1 gallon of sirup. The equa- tion is: 86 where a = the numberofgallonsofsap to produce 1 gallon of standard-density sirup. X = the Brix value of the sap (to represent the solids concentration of the sap). Fi"om this number, 1 is subtracted to obtain the number of gallons of water that must be evaporated from the sap to obtain 1 gallon of sirup. The following equation is used: 86 Example: With sap having a density of 2.4° Brix, S6_ 2.4 1, or 36 - 1 = 35, the number of gallons of water that must be evaporated to obtain 1 gallon of standard-den- sity sirup. Ride of 86 The amount of water that must be removed to reduce the sap to sirup varies with the solids concentration of the sap. The "Rule of 86" can be applied to determine the number of gallons of a particular sap re- quired to produce 1 gallon of standard-density sirup. The number 86 is used in the calculation as representative of the percentage of solids (as sugar) on a weight-volume basis that is found in a gallon of standard-density sirup. (Until 1974 the standard density for maple sirup was 65.5° Brix, and sirup of this density contains 86.3 percent solids as sugar. Now that the standard density is 66.0° Brix, the percentage of sugar in a gallon of standard sirup is actually 87.2, but the traditional "Rule of 86" persists in the industry and is quite satisfactory for practi- cal purposes.) Since the solids concentration of sap is com- paratively low, its Brix value and percentage of solids (weight-volume) are essentially the same. Suniniaiy (1) The modern evaporator is an open-pan, flue type and has a high evaporation efficiency. (2) The major changes that affect sirup quality, color, and flavor occur after the sap has been concentrated to 45° Brix. (3) The development of color and flavor depend on the length of time sap with a Brix value of 45° or higher is boiled. (4) Evaporation rate is increased if the path the sap travels over the heated surfaces is lengthened. (5) Use of multiple sap pans assembled in series increases the rate of evaporation. (6) The time required for the last stage of evaporation is determined by the holdup time (depth of sap in evaporator, last section or in finishing pan) and the intensity of the heat. (7) Pi'oduction of light-colored sirup is favored by shallow depth of sap in the evaporator and by intense constant heat. MAPLE SIRUP PRODUCERS MANUAL OPERATING THE EVAPORATOR 49 Starting the Evaporatoi- The sap is run into the evaporator until the bottom of the front pan is covered to a depth of 1 inch; then the fire is lit. As soon as the sap begins to boil, the sap inlet float valve is ad- justed to maintain the desired depth of liquid (V2 to 1 inch) in the sirup pan. As water evapo- rates, the float valve admits more sap (fig. 79). If sirup has not been made previously, a series of adjustments of the float will be neces- sary to be sure the liquid in the sirup pan i always maintained at a depth of '/., to 1 inch at the point of drawoff. The constant addition of sap keeps the sap in the pan dilute. It becomes progressively more concentrated at points farther from the sap inlet. The sirup di-awoff is at the farthest point. Saps of different solids concentrations (° Brix) require different adjustments of the inlet-valve regulator to maintain the same depth of sirup in the front pan. The depth of sap in the sap pan must be gi-eater for sap with a Brix value of 1° than for sap with a Brix value of 2° and it must be lower for sap with a Brix value of 3°. By checking the Brix value of the sap in the storage tank, the float valve can be set to maintain the desired depth of sap in the evapo- rator. The Brix value should be checked with a hydrometer every half hour or whenever a new lot of sap is run into the storage tank. This will prevent burning the pan, which might happen with a change to sap with a lower BrLx value unless the depth of liquid is increased. The pipeline between the storage tank and the evaporator must be large enough to assure a constant and adequate supply of sap to the evaporator, so that a constant level of sap is maintained. If this pipe is connected to an outside storage tank, it must be insulated to prevent the sap from freezing in the line. Were this to occur, the supply of sap would be cut off and the pans would burn. The sap feed line should be equipped with a fast-acting valve that can be used to adjust the flow of sap and to stop the flow when the evaporator is taken out of use. A secondary sap feed line should also be installed. This line should be equipped with a flexible hose long enough to reach any part of the evaporator or finishing pan. This is an emergency line for use whenever there is a stoppage in the main feed line or for quickly supplying sap to any part of the evaporator where sap is needed to prevent burning the evaporator. Drawing Off the Siiiip The boiling point of standard-density sirup is 7° F. above the boiling point of water. This is discussed in detail in the section "Elevation of Boiling Point," page 72. Any thermometer that has a range of 200° to 230° F. and a sufficiently open scale can be used to determine the boiling point of sirup. It should be calibrated in V2° and preferably in V4°. With older procedures, it was customary to make finished sirup in the evaporator. It was seldom possible to continuously remove sirup of standard density from the sirup pan, except in very large evaporators. Instead, the sirup was removed discontinuously or in batches. The last channel of the sirup pan was in effect a finish- ing pan. This caused the following undesirable conditions: The sirup channel was seldom iso- lated, so that the turbulence of the boiling sirup caused a constant intermixing of the finished or nearly finished sirup with less concentrated sap. This lengthened the holdup time (time sap is heated) and occurred when heating is a critical factor in flavor and color development. Also, each time a lot of finished sirup was drawn off, some sirup had to be left in the last channel of the evaporator to keep the evapora- tor from burning. The sirup that was left was then mixed with the next lot of dilute sirup. The prolonged heating period darkened the color. However, when this procedure is followed, the drawoff valve must be opened as soon as the boiling sirup reaches a temperature 7° F. above that of boiling water. The temperature of the boiling sirup should be watched closely to be sure it neither rises above nor falls below this temperature, and the sirup should be drawn off at a rate to maintain this tempera- ture. If the boiling sirup falls below the proper temperature, the drawoff valve should be closed immediately. 50 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Finishing Pan Because of the difficulties of finishing the sirup in the evaporator, use of a separate fin- ishing pan is recommended (figs. 80 and 81). A separate finishing pan permits (1) complete re- moval of the almost finished sirup (45° to 60° Brix) from the evaporator, so that there is no possibility of intermixing with less concen- trated sirup; (2) complete control of finishing the sirup without extending the total time the sap is heated; and (3) complete removal of the finished sirup from the pan. The size of the finishing pan is determined by the size of the evaporator. Partly finished sirup should be removed ft-om the evaporator at least once each hour and finished in batches. Since sirup transferred to the finishing pan will have a solids concentration of not less than 45° Brix and since it requires 2 gallons of 45°-Brix sirup to yield 1 gallon of 66.0°-Brix (standard-density) sirup, an evaporator that has a rated capacity of 4 gallons of finished sirup per hour requires a finishing pan that holds 8 gallons of 45°-Brix sap and provides additional space to take care of foaming. A pan 18 inches square will hold approximately 1.5 gallons for each inch of depth. Therefore, to accommodate 8 gallons of 45°-Brix sap the pan should be 5 inches deep and should have an additional 10 inches for foaming. The pan will therefore be 18 inches square and 15 inches deep. It should have handles and a cover and should be equipped with a precision thermometer having a range of 200° to 230° F. in V2° or preferably V4° divisions and a sirup drawoff cock. Preferably, the pan should be heated by gas flame since gas heat can be easily adjusted and can be shut off when the sirup reaches the desired boiling tempera- ture. For convenience two finishing pans can be used alternately. When a finishing pan is used, the sap being drawn from the evaporator for transfer to the finishing pan need not be of constant density. It can be any density above 45° Brix (3° or more above the boiling point of water). The higher the density of the sirup that is withdrawn from the evaporator, the smaller the amount of liquid that has to be evaporated in the finishing pan. Another and important advantage of using a finishing pan is that it permits filtering the m m mmM. 1 ' 1 ^ H PN-4776 Figure 80. — The finishing pan allows complete control over the final stage of the evaporation of sap to sirup. Generally, the fuel is bottled gas. sirup that is being transferred from the evapo- rator to the finishing pan. Sirup at this density (45° to 60° Brix) has essentially all of its sugar sand (see p. 78) precipitated. At this density, it has a viscosity (fluidity) only slightly higher than water and filters much more readily than does standard-density sirup. In some installations, the sirup is pumped from the finishing pan to the holding or can- ning tank. A cartridge-type filter can be placed in this pipeline to serve as a polishing filter. It will remove any sugar sand that was not re- moved by the major filter or that may have been formed in the finishing pan. Many producers using bottled gas to heat the finishing pan report that the cost of fuel is approximately 7 cents per gallon of finished sirup. A finishing pan is always used in conjunction with a complete evaporator (flue pan plus flat pan). The flat or sirup pan of the evaporator serves as a semifinishing pan. The capacity of the evaporator is readily expanded by adding one or more flue (sap) pans, each with its own arch and separate heat source (preferably oil). MAPLE SIRUP PRODUCERS MANUAL 51 PN-4771 Figure 81.— A steam-heated finishing pan, Uke a gas-fired pan, provides positive control of the finished sirup and eliminates danger of scorching. When a finishing pan is used, the following procedures should be observed: (1) Do not finish more than 5 to 10 gallons of sirup in a batch. (2) When the sirup is finished, that is, when it reaches the proper temperature (7° F. above the exact boiling point of water), heating must be stopped immediately. (3) Drain all the finished sirup from the pan. If any sirup is left in the pan, it will darken the next batch. (4) Use two finishing pans alternately. Aiitoinatic Drawoff An automatic drawoff is well suited for draw- ing the partly evaporated sap from the evapo- rator for later completion in the finishing pan (fig. 82). A high precision thermoregulator is not required, since a tolerance of ±0.5° F. is accept- able. Corrections need not be made for slight changes in the boiling point caused by changes in barometric pressures throughout the day. Automatic valves can be purchased as com- plete packages, or they can be assembled as indicated in chart 10. These valves are operated by a solenoid, which in turn is opei-ated by a thermoregulator. The thermoregulator is ad- justed by hand to open or close the valve when the boiling sirup reaches the desired tempera- ture, as measured by a precision thermometer. A thermoregulator, if used to control the removal of finished sirup from the evaporator 52 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE AUTOMATIC SIRUP DRAW OFF MECHANICAL ASSEMBLY EVAPORATOR PAN \ THERMO-i SWITCH 0 5 MICROFARAD 600 VOLT OIL-FILLED CONDENSER OR TYPE 8A5PS5 (ITT) FEDERAL CONTACT PROTECTOR FOR 117 V AC OR EQUAL Chart 10. — Automatic sirup drawoff. or finishing pan, must be sensitive to changes of ±0.1° F. The thermoregulator must be recaH- brated three times a day. When the thermoregulator is operated on 110 V. a.c, a condenser must be shunted across the line (see chart 10) to protect the contact points against the surge of heavy current that is set up each time the solenoid coil operates. To avoid this, it is better to operate the thermo- switch on low d.c. voltage and use a high- capacity mercury relay to operate the solenoid valve. Another type of temperature regulator uses thermistor probes as the sensing element. A sensitive electrical relay must be used w^ith this type of regulator, and it is recommended for use with the thermoregulator. The thermistor probes in the boiling sirup must be kept free of sugar-sand deposits. De- posits of sugar sand on the probes will change their heat-transmitting properties and cause error in their response to the sirup boiling temperatures. The probes can be kept free of sugar sand by soaking them in 10-percent sul- famic acid between runs. This same precaution applies to the bulb of the thermometer. A further advance in controlling automatic drawoff has been made at the Eastern Regional Research Center (15). A new thermoregulator PN-n78 Figure 82. — The automatic drawoff is especially well suited for removing sirup from the evaporator. When a finishing pan is used, the evaporator functions as a semifinishing pan. containing a Wheatstone bridge, thermistor probes, and a meter relay automatically com- pensates for changes in boiling point caused by changes in barometric pressure (fig. 83). The instrument employs two thermistor probes. The water probe continually responds to changes in the temperature of boiling water. The sirup probe causes the valve to open whenever the temperature of the boiling sirup reaches a pre- determined number of degrees above the tem- perature of the boiling water — T F. for stand- ard-density sirup and slightly more for heavier sirup. End uf an Eva|K>i'ation When the evaporation of a run of sap has been completed, care must be taken or the pans may be burned. If water is available, it can be run into the storage tank as the last of the sap is being withdrawn. Little sap will be lost, and the pans can be flooded with .3 to 5 inches of water before the fire is extinguished. This pre- caution is necessai-y when either wood or oil is used because enough heat will remain in the MAPLE SIRUP PRODUCERS MANUAL 53 Figure 8S.— Automatic thermoregulator that compen- sates for changes in barometric pressure. firebox and arch to melt the solder and the thin metal of the pans if the pans become dry before the firebox has cooled. If water is not available, the fires must be extinguished and evaporation stopped while there is still enough sap in the storage tank to fill the evaporator to a depth of 3 to 5 inches. Cleaning the Evaporator When maple sap is concentrated to sirup in a flue-type open-pan evaporator, the organic salts become supersaturated; that is, they are con- centrated to a point where they can no longer be held in solution. They are then deposited on the sides and bottom of the evaporator as a precipitate or scale. This scale forms an imper- vious layer that builds up with continued use of the evaporator. The scale reduces heat-transfer efficiency and thus wastes fuel and holds up sirup in the evaporator unduly. The scale is of two types. One type is a protein-like material that forms in the flue or sap pans. The other, called sugar-sand scale, forms in the sirup or finishing pan. It is a calcium and magnesium salt deposit similar to milkstone and boiler scale. Sugar-sand scale is the more troublesome of the two types. It is esi^ecially troublesome if it is allowed to build up to an appreciable thick- ness. Also, sugar sand contains entrapped cara- melized sugar, which contributes to the produc- tion of dark-colored sirup. Removing sugar-sand scale is not easy, and doing it by physical means (scraping, scrubbing with steel brushes, or chiseling) is almost im- possible. Removal becomes more difficult as the layer of scale becomes thicker. Clean the evapo- rators often enough to prevent buildup of sugar sand. Teflon-coated pans are easier to clean. Also, keep the underside of the flues clean. Mptlioils I'scd ill file Past Some methods used in the past to prevent formation of scale and to remove thin layers include — (1) Reversing the flow of sap through the evaporator, according to the manufacturer's directions; this retards the formation of scale. (2) Running soft spring water through the evaporator for a long period; this tends to dissolve small amounts of scale. (3) Pouring skim milk into the pan and letting it remain until it sours; the lactic acid of the sour milk has some solvent action on the scale. (.Iieiiiirtil (.le«>rator Milk-concentration or fruit-juice evaporation plants in maple-producing areas can be adapted for evaporating maple sap. This was done dur- ing the 1930's at Antigo, Wis., where a milk plant was used to make sirup during part of the day in the spring sirup season (3). The procedure used at Antigo is as follows: The sap is concentrated to between 25° and 30° Brix in the conventional open-pan evaporator at the farm site. This is 90 percent of the required evaporation. Evaporation is completed in a vacuum evaporator at the central sirup- finishing plant. This two-stage method of evap- oration results in a nearly colorless and flavor- less maple sirup. Such sirup is not marketed for direct use, but it is ideal for the production of high-flavored sirup, as described on page 106. A study at Cornell (42) showed that the use of milk-plant equipment during off-jieak seasons for evaporating maple sap was practicable but that the sirup pi-oduced had to be treated by the high-flavoring process to obtain marketable maple sirup. The fixed costs for use of milk- plant equipment are negligible. However, the perishable, partly concentrated sap must be transported to the milk-concentrating plant, and use of a central sirup-finishing plant re- quires a new procedure for maple-sirup produc- tion. Siimiiiaiy (1) The steam evaporator provides a steady source of heat, and danger of scorching is minimized. The sirup produced is light col- ored and delicately flavored. However, the steam evajwrator is expensive to install. A combination oil-and-steam system (two- stage method of evaporation) is proving suc- cessful; it has all the advantages of steam but is less expensive to install. 58 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE (2) The vacuum evaporator, which is Hmited to large-scale or central-plant operation, is used to complete the evaporation of sap that has been partly concentrated on the farm. The equipment used usually is idle milk- evaporation equipment. The sirup produced has essentially no maple flavor, but it is excellent for use in making high-flavored sirup. FUEL Wood The modern flue-type evaporator was de- signed for burning wood. A wood fire carries a luminous flame throughout the entire length of the arch. The flue area of the evaporator and the part that lies over the firebox are heated both by radiant and by convection heat liber- ated by the burning gases. The wood may be sound cordwood, defective trees removed in improvement cuttings, or sawmill wastes — either culls or slab (69). In the evaporation process, the object is to evaporate the water in the shortest possible time. Therefore, it is essential to use only diy, sound wood that will produce a hot fire. Wet or green wood will not produce as much heat as will the same volume of dry wood. Poor burning fuel results in a slower boiling rate. This, in turn, causes the sap to be held in the evapora- tor for a longer time and results in a darker sirup. A steady fire shortens the boiling time. The best results are obtained by charging the fire- box first on one side and then on the other, keeping the fuel in the firebox at almost con- stant volume (fig. 87). The fire doors should be closed immediately after each charging to re- duce the intake of cold air which cools the underside of the pans. When this happens, the boiling rate of the sap decreases and holdup time in the evaporator increases. Likewise, ash- pit draft doors that are open too wide will admit more air than is required for combustion, and the excess air has a cooling effect. Introduction of cold air beneath the evaporator pan in either the firebox or the flue area not only reduces the boiling rate but also tends to set up counter currents in the flowing sirup in the different channels of the evaporator. This also contrib- utes to the production of a darker sirup. Based on $25 per cord of wood, the fuel to produce a gallon of sirup would cost about $L This represents about 10 percent of the cost of sirup production (5, 113). The heating values of different wood fuels expressed in British ther- mal units (B.t.u.'s) for a standard 4- by 4- by 8- foot cord are maple, 22,800,000; beech, 20,900,000; and hickory, 24,800,000. oa The advantages offered by using oil as the heat source for evaporating maple sap to sirup are numerous (lOi). Chief among these are (1) it is automatic; therefore, it does not require the services of a fireman; (2) it provides a steady uniform heat, which is desirable for producing high-quality sirup; (3) it is clean and therefore aids in better housekeeping and sanitation in the evaporator house; and (4) in terms of Brit- ish thermal units, the cost of oil at 35 cents per PN^783 Figure S7.— When both doors are opened for firing, the excess air admitted chills the pan. Boiling stops; sap and partly evaporated sirup intermix; and then, when the fuel is again burning briskly, the evaporator must equilibrate itself. MAPLE SIRUP PRODUCERS MANUAL 59 gallon is more than double the cost of wood at $25 per cord, but the operational costs may not differ greatly since oil does not require the services of a fireman. The disadvantages of using oil as the fuel source, while few, are nevertheless important: (1) The initial cost (capital investment) of oil burners is high; (2) oil burners require a special arch (firebox) although in a new installation it is not necessarily more expensive than the conventional wood-burning arch; and (3) oil does not make use of the cull trees that must be removed each year from a well-managed sugar bush. When oil is used as fuel, two pertinent facts must be observed. The first and most important is that wood and oil burn in different ways. Wood burns with a luminous flame (long fire path) throughout the length of the evaporator, including the area under the flue pans as well as under the sirup pan; oil, on the other hand, burns as a ball of flame in only a relatively small space. Secondly, of the two forms of heat transfers — radiant and convection — used in a sap evaporator, radiant heat accounts for ap- proximately 80 percent of the heat transfeiTed to the liquid, whereas convection heat (that which is derived from the hot flue gases passing over the surface of the pans and flues) supplies approximately 20 percent. Therefore, to make use of the radiant heat from the oil fire, the ball of burning oil must illuminate the entire under- surface of the pans. This necessitates properly positioning the ball of burning oil and eliminat- ing any obstructions that will prevent illumina- tion of the entire undersurface of the pans. This requirement will be met only through the proper design of arches made for the burning of oil as fuel. A wood-burning arch cannot be successfully converted to an oil-burning arch without major changes. The principal fault of such a conver- sion is that the slope of the wood-burning arch behind the firebox does not permit illumination of the entire underside of the sap or flue pan by the ball of burning oil and, consequently, the sap will not boil. Size of Burner The size of burner to use is determined by two factors: (1) The length and width of the evaporator (the vertical area of the flues has a minor effect) and (2) the quantity of sap to be evaporated per hour. If the rated capacity of the evaporator in gallons of sap per hour is known, it can be divided by 13 (the approximate number of gallons of water evaporated per hour by 1 gallon of oil) to obtain the size of burner (g.p.h. = gallons of oil per hour) required for a specific evaporator. The rated capacity of an evaporator burning wood cannot be accurately equated to that of an evaporator burning oil. Therefore, this method of calculation may indicate a burner that is too large. However, this is not serious since the amount of oil burned per hour can be changed, within limits, by changing the size of the nozzles. To prevent damaging the pan by firing with an oversize burner, it is recommended that for the first trials a nozzle size 20 percent smaller than indicated by the above calculation be used. The burning rate (nozzle size) can then be increased as needed. An empirical method for determining nozzle size is to divide the surface area (length times width) by .5. Thus, a 5- by 12- foot evaporator would require an oil burner nozzle of 12 g.p.h. Tyite of Burner With few exceptions, high-pressure oil burn- ers that use No. 2 oil are recommended. They are available with different nozzle sizes to fit evaporators of all sizes. Their lower initial cost offsets any advantage gained by using burners that require the heavier grades of oil. Muniber of Burners per Arch Only one burner is required for each evapora- tor (fig. 88). It must be correctly positioned under the evaporator and the combustion chamber must meet certain minimum stand- ards. Use of a single burner reduces the capital investment and installation costs. For example, the capital investment and installation costs for an evaporator requiring 12 gallons of fuel per hour supplied by a single burner would be approximately half that for an evaporator sup- plied by two 6-gallon-pei--hour burners. In addi- tion, the two smaller burners will require more servicing and attention than will the larger one. 60 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN-4'H.l Figure S8. — A correctly positioned, single, high-pressure, domestic-type burner will give the required heat for the evaporation of the sap. If one burner is used, it should be mounted far enough below the bottom of the pan so that the radiant heat will be effective across the full width of the pan. If construction of the arch does not permit mounting the burner this far below the pan (see table 5), then two or more smaller burners mounted horizontally should be used to insure heating the full width of the pan (fig. 89). If the slope of the arch is such that the undersurface of the flue pan cannot be illuminated by the ball of fire (see chart 12), boiling may not occur in the area not illumi- nated. This is especially true of wood fuel arches that have been converted for oil burn- ers. To compensate for this, a supplementaiy firebox can be constructed under the flue pan. and another burner mounted; however, this is not always satisfactoiy. \ftzzh' Tip For evaporators in which the length is ap- proximately twice the width, the nozzle tip should be at an 80° angle. For evaporators in which the length is greater than twice the width, the nozzle should be at a 60° angle. Irrespective of the type of nozzle tip or the angle, the burner must be adjusted so that the PN-47S5 Figure 89. — When one large burner cannot be mounted sufficiently far below the pan, two or more .smaller burners can be mounted horizontally to give the re- quired amount of heat without danger of producing hot spots. correct amount of air is fed along with the atomized oil to insure complete combustion. This can be checked with a flue gas analyzer. Arvh ,1 ( ihiisti ( h The arch for oil fuel also serves as a support for the evaporator pans and contains the com- bustion chamber and the flue for the hot gases. The arch should be located in the evaporator house to provide an adequate working space with room for installing supplemental arches as the operation is expanded. The arch need not be in the center of the evaporator house but may be at one side. The concrete footings for the arch should be on gravel and should extend below the frostline. An all-masonry arch, with external walls built of cinder block or brick, may be built on the site, or the arch may be prefabricated with exterior walls of sheet metal on a cast iron and steel frame. In either case, it must conform to certain minimum dimensions. The interior construction is similar for both. Dinu-nsioiia <>/ trr/i.— The size (length and width) of the arch is determined by the size of the evaporator. It must be wide enough to support the pans and long enough not only to support the pans but also to hold the base of the flue-gas stack. Chart 12 shows a masonry arch for a 5- by 12- foot evaporator (9- foot flue pan and 3- foot flat pan). The outside walls are MAPLE SIRUP PRODUCERS MANUAL 61 Cinder till, may have I" fire brick facing Combustion chamber Insulating fire brick (2800° F, ) — Cinder brick Firebrick, zS'V X 4'/2" X 9" LONGITUDINAL SECTION T i i T T I i CROSS SECTION Chart ;^.— Arch and firebox for oil-fired evaporator. cinder block except for the top section, which is 3V2-inch bricks to provide a 2-inch supporting surface for the pans and project IV2 inches beyond the pans. If the arch is made to the exact outside dimensions of the pans, the sup- porting wall of the arch would cover too much of the underpan surface (3V2 inches on all sides). A large loss of heating surface would result. The height of the ai'ch is governed by the size of the combustion chamber, which in turn is governed by the size of the burner (see table 5) and the size of the evaporator. For a 5- by 12- foot evaporator, the height of the arch should be 46 inches (chart 12). The arch should elevate the pans 46 inches or more above the floor level to permit the use of gravity flow of the sirup in successive operations. If the arch raises the pans too high, especially when multiple evapo- rators are used, a catwalk can be installed; or the combustion chamber of the arch and the burner can be built in a pit. Firebox and (.ombustioii Chamber. — The entire open space enclosed by the arch under the pans is the firebox. Better results will be obtained if it contains a combustion chamber (see chart 12). The function of this chamber is (1) to provide a hot radiating surface and (2) to utilize the hot, incandescent surface to vaporize and insure complete combustion of the oil. For maximum efficiency, the size of this com- bustion chamber must conform to minimum dimensions that are related to the nozzle size of the burner. These dimensions are given in table 5. A rule-of-thumb relation between combus- tion chamber and nozzle size is that there should be a floor area of 90 square inches for each gallon per hour of rated nozzle capacity. The distance between the top of the combus- tion chamber and the bottom of the pans (di- mension D of chart 12) is important for two reasons: (1) The ball of burning oil should be far enough below the "cold" pan surface to prevent 62 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Table 5. — Inside dimensions of combustion chamber and stack diameters Distance from center burner Burning rate of draft tube oil (g.p.h.) to combus- tion cham- ber floor (A) Minimum height (B) (C) Distance between Length for nozzle combustion angle of- chamber and top of arch (D) (E) Width for nozzle angle of — 80° Approxi- Minimum mate floor diameter of area stack Inches inches 5 9 18 6 9 18 7 10 19 8 11 19 9 11.5 19 10 12 19 12 13 20 14 14 21 16 15 22 18 16 23 20 17 24 22 18 25 24 19 25 Inches Inches Inches Inches 25 27 29 30 32 33 36 39 41 44 47 49 51 21 23 25 26 28 29 32 35 37 40 42 44 46 Square inches 450 540 630 720 810 900 1,080 1,260 1,440 1,620 1,800 1,980 2,160 Inches 10 10 10 12 12 12 12 14 14 16 18 20 20 corrosive deposits on the underside of the pan; and (2) the ball of fire must be far enough below the pan so that the acute angle of radiation from the apex (ball of fire) to the extreme sides of the pan is kept to a minimum (table 5). If the ball of fire is too close to the pan, there is insufficient space between the pans and the top of the combustion chamber; and the angle of radiation becomes too great. This results in uneven heating across the width of the pan. Overheating occurs directly over the fire. This can be compensated for only by using more than one burner mounted horizontally. Construction of Arch and I'onibiistion C.httmher Arches may be made of sheet metal or ma- sonry (chart 12). In arches made of either mate- rial, the combustion chamber is free standing within the arch and is constructed of insulating firebrick. In sheet-metal arches the remainder of the arch is lined with hard firebrick. The combustion chamber is separated from the ex- terior wall of the arch by an air space to allow for expansion of the heated bricks. For the same reason, there is an air space between the hard firebrick liner and the exterior walls of the arch. The fill between the combustion chamber and the rear of the arch must be of a nonpack- ing material such as cinders. Size of Stack Since the oil burner is operated under forced draft, the flue stack need not be as high or as wide as when wood is the fuel. The size of the stack is governed by the size of the oil burner (table 5). With only one arch, it is recommended that a complete evaporator, flat pan, and flue pan be used. However, it is also recommended that the flue pan be at least two-thirds the total length of the evaporator. The flat pan serves as the semifinishing pan in which the sap is raised to a density of 55° or 60° Brix. The partly concen- trated sap should be transferred from the evap- orator to the finishing pan where the final stage of evaporation is completed. Although sap can be concentrated to sirup in the evaporator, this practice is not advised. Installation of Multiple Arches To increase the capacity of the evaporator, additional arches and pans can be added. Each additional arch should be equipped with a flue MAPLE SIRUP PRODUCERS MANUAL 63 pan only and should be installed ahead of and in series with the complete evaporator (see chart 13). The supplemental flue pan arches are constructed in exactly the same manner as the one for the complete evaporator. To connect the supplemental flue pans in series with the evap- orator requires only one point at which the raw sap is fed and one point at which the partly evaporated sap or sirup is removed for transfer to the finishing pan or bottling tank. In the multiple unit assembly, the flat pan of the evaporator continues to serve as the semifinish- ing or finishing pan (fig. 90). Efficiency af Heat A study of the use of oil as fuel for the evaporation of maple sap in an open evaporator was reported by Phillips and Homiller (87). They showed that commercial maple sap evapo- rators fired with oil haye an efficiency of 66 to 74 percent. Their data were obtained with a smaller-than-average evaporator; larger evapo- rators would be expected to be slightly more efficient. The efficiency of the open pan evapo- rator compares favorably with commercial steam generating plants, for which a combus- tion efficiency of 80 percent is considered good. The efficiencies obtained by Strolle and oth- ers (111) in evaporating 45 to 55 gallons of 3°- Brix sap to standard-density sirup are given in table 6. These data indicate that efficiency de- creases as the rate of sap feed (gallons of sap evaporated per hour) increases and that oil cost per hour also increases. However, from further Figure 90.— In one of the most economical and efficient types of evaporators, an oil fire and four fine pans are used for evaporation; high-pressure steam is used for the last stage of evaporation. 64 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE FLOW DIAGRAM OF MULTIPLE UNIT EVAPORATOR OIL FIRED FINISHING PAN (GAS FIRED) TO POLISHING FILTER AND CANNING TANK Chart 13. — Flow diagram of multiple-unit evaporator. calculations and rough extrajX)lations the data in table 7 were obtained. These data show that sirup production in- creases as the amount of fuel burned increases. The increase in cost of fuel per gallon of sirup is slight and is more than compensated for by the improvement in the gi-ade of the sirup and the reduction in evaporation time and cost of labor. Table 6. — Efficiency of oil-fired experimental evaporator in evaporating sap of 3° Brix to standard-density sirup Sap evaporated per hour (gallons) Oil burned per hour Efficiency 45 50 55 Gallons 3.9 4.7 5.3 Percent 74 69 66 Table 7. — Extrapolated efficiency of oil-fired evaporator Sap evapo rated per hour (gallons) Cost of Oil Sirup oil per burned made gallon of per hour per hour sirup produced Time re- quired to evapo- rate 550 gallons of sap Effi- ciency Galloyis Gallons Dollars Hoiirs Percent 65 6.7 60 6.0 55 5.3 50 4.7 45 3.9 2.36 1.00 8.5 59.6 2.18 .96 9.2 62.6 2.00 .93 10.0 66 1.82 .91 11.0 69 1.64 .84 12.2 74 The maximum efficiency that could theoret- ically be obtained from an oil-fired evaporator would utilize all the British thermal units (B.t.u.'s) of a gallon of oil. This heat would raise the temperature of the feed sap to its boiling point and then vaporize the water in the sap to steam. Assuming that the temperature of the sap is 35° F. and its boiling point is 210°, the heat (B.t.u.'s) required to evaporate 34.4 gallons of sap with a density of 2.5° Brix to yield 1 gallon of standard-density sirup can be calcu- lated. Knowing the B.t.u.'s of No. 2 fuel oil (139,000), the number of gallons of oil required to produce this gallon of sirup at maximum efficiency is 2.2 gallons. Since no oil burner is 100-percent efficient, and oil-fired evaporators are only 60- to 75-percent efficient, the fuel required per gallon of sirup is 3+ gallons of oil. To measure the efficiency of burners, arches, and evaporators, a number of factors must be carefully obtained. These are: MAPLE SIRUP PRODUCERS MANUAL 65 (1) The Brix Value of the Raw Sap.— For example, only half as much water is evaporated from 3°-Brix sap as from a lV2°-Brix sap to make standard-density sirup. Therefore, other things being equal, it would require only half as much oil to make sirup from 3°-Brix sap as from lV2°-Brix sap. (2) Temperature of Sap. — The temperature of the sap as it enters the evaporator must be noted, since a great deal of heat is required just to heat the sap from its storage temperature to its boiling temperature. Therefore, the warmer the sap, the less oil required to heat it to boiling. (3) The Brix Value of the Finished Sirup.— AW too often the exact Brix value of the finished sirup is not considered in making efficiency studies. Yet a difference of only a few tenths of 1° in Brix value has a pronounced effect on the number of gallons of sap that must be evapo- rated to produce the sirup. For cost accounting records, most producers will find that merely to divide the number of gallons of sirup made by the number of gallons of oil burned will give the fuel costs per gallon of sirup. These data should be considered an estimate of the efficiency of the oil-burner in- stallation. The cost of fuel oil can be kept low by con- tracting for it through competitive bidding. The heat (B.t.u.'s) produced by one cord of wood is approximately equivalent to that produced by 175 gallons of oil. The efficiency of wood de- pends on many variables, such as condition of the wood, size of the individual pieces, how it is fired, condition of the fire, and stack height. Summary' (1) Wood (a) Use only well-seasoned dry wood, either cord or slab. (b) Keep a steady fire. (c) Fire first on one side of the firebox, then on the other. (d) Keep the fire doors ojien only long enough to charge the firebox. (e) Ojjen the dampers and draft doors only enough to furnish the air for combustion. (2) Oil (a) Oil is recommended if there is a shortage of labor. (b) The firebox and arch must be specially built. (c) The cost of fuel for making sirup is ap- proximately the same for oil and wood. (3) Increase the capacity of the evaporator through the addition of one or more sap or flue pans. (4) Mount the supplemental pans on their indi- vidual arches. (5) Hook up the supplemental arches in series with the evaporator. (6) Use a finishing pan. MAPLE SIRUP The characteristics of maple sirup are dis- cussed here so that the development of color and flavor will be better understood. (Composition of Sap and Sirup Table 8 gives the composition of maple sap and sirup. The analyses in this and later tables are not average values; they are analyses of typical saps and sirups. Usually the sirup and sap have essentially the same composition, ex- cept that on an "as is" basis the constituents of the sirup show a thirtyfcld to fiftyfold increase as a result of concentrating the sap to sirup. The amounts of some of the constituents, when expressed on a dry-weight basis, are less in sirup than in sap because of their removal from solution as insoluble sugar sand. The different kinds of sugar in maple sap are not numerous (91). Sucrose, the same sugar as in cane sugar, comprises 96 percent of the dry matter of the sap and 99.95 percent of the total sugar (table 9). The other 0.05 percent is com- posed of raffinose together with three unidenti- fied oligosaccharides. Un fermented sap does not contain any simple or hexose sugars. The sap contains a relatively large number of nonvolatile organic acids (table 10), even though they account for only a small proportion of the solids (89). The concentration of malic acid is 10 times that of other organic acids. If 66 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Table 8. — Composition ofynaple sap and sirup ' Sap Sap (dry Sirup (dry weiRlit) weight) Percent Percent Percent Sugars 2.000 97.0 98.0 Organic acids .030 ^1.5 .3 Ash .014 ".7 .8 Protein .008 .4 .4 Unaccounted for __ .009 .4 .5 ' Typical values, not averages. Maple sap and sirup vary in composition between rather wide limits. Table 9. — Siigars in maple sap and sirup Sugars Sap Sap (dry weight) Sirup (dry weight) Hexoses Sucrose Raffinose and a Percent _ 0 . 1.44 ^ .00021 .00018 .00020 .00042 Percent 0 96.00 .014 .013 .014 .028 Percent 0-12 88-99 glycosyl sucrose _ Oligosaccharides: - I II III ' Typical values, not averages. ■ The oligosaccharides have been isolated by chroma- tography but have not been identified. may prove to be useful in detecting adultera- tion (151). One or more of these acids may be important in forming "maple flavor." Sap con- tains soluble ligninlike substances that are in- volved in the formation of maple flavor (117). The ash or mineral matter (table 11) accounts for only 0.66 percent of the whole sirup, or 1 percent of the dry solids. Although the minerals are only a minor part of the sirup, they have been useful in establishing the purity of maple sirup and they contribute an astringency to the sirup that many find desirable. Calcium, a part of the ash, is responsible for the sugar-sand scale, calcium malate, which forms on the pans (18). The low sodium and high potassium content of the ash suggests the use of maple in dietary foods. Composition of sugar sand ranges as follows U8): Range Sugar sand in run percent__ 0.05- 1.42 pH 6.30- 7.20 Ca percent-. 0.61-10.91 K do 0.146-0.380 Mg do 0.011-0.190 Mn do — _ 0.06- 0.29 P .... do 0.03- 1.18 Fe p.p.m... 38-1,250 Cu p.p.m._. 7- 143 B p.p.m..^ 3.4- 23 Mo p.p.m... 0.17- 2.46 Free acid percent-^ 0.07- 0.37 Total malic acid do 0.76-38.87 Acids other than malic do 0.08-2.62 Undetermined material do 6.94-34.16 Calcium malate do 1.30^9.41 Sugars in dried samples do 33.90-85.74 Sugar sand in dried samples do 14.26-66.09 Table 10. — Nonvolatile organic acids in maple sap and sirup ' Acid Sap Sap (dry weight) Sirup (dry weight) Percent 0.021 .002 .0003 .0003 .000 Trace 0 Percent 1.40 .13 .02 .02 .L«0 Trace 0 Percent 0.141 Citric .015 .012 .006 Glycolic or dihydroxybutyric- Unidentified acids: I, II, III, IV V, VI, VII .006 Trace Trace ' Typical values, not averages. Table 11. — Mineral composition of maple sirup ' Item Sirup Diy weight Soluble ash Insoluble ash ... Percent 0.38 .28 Percent 0.58 .42 Total ash ... .66 1.00 Potassium Calcium .26 .07 .40 .11 Silicon oxide Manganese .02 .005 .003 .03 .008 .005 Magnesium Trace Trace ' Typical values, not averages. MAPLE SIRUP PRODUCERS MANUAL 67 The nitrogenous matter constitutes only a small part of the total solids (88).'' Expressed as nitrogen, the sap contains only 0.0013 percent and the sirup 0.06 percent. The sap does not contain any free amino acids except late in the sap-flow season. Nitrogen occurs only in the form of peptides. Whether the nitrogenous mat- ter enters into the formation of maple color or flavor is an open question. An increase in free amino acids is associated with the development of "buddy sap." FORMATION OF TRIOSES FROM SUCROSE HYDROLYSIS OF SUCROSE C|2 HjjO,, (SUCROSE) FISSION OF HEXOSES (HEXOSES) ► Cg HiaOe + CsHjOg (GLUCOSE) (FRUCTOSE) (.olor anti Flavor Maple sap as it comes from the tree is a sterile, ciystal-clear liquid with a sweet taste. None of the brown color or flavor that we associate with maple sirup is in the sap. This is easily demonstrated by collecting sap asepti- cally, freezing it, and then freeze-drying it. The solid obtained is white or very light yellow and has only a sweet taste. The typical color and flavor of maple sirup are the result of chemical reactions, involving certain substances in the sap, brought about by heat as the sap boils (H8). Since at least one of the products of the reaction is the brown color, it is known as a browning reaction. Neither the exact nature of this reaction nor the identity of the reacting substances is known. Indications are that one or more of the 6 sugars or their degradation products and one or more of the 12 organic acids in maple sap are involved in the browning reaction. Experimental evidence indicates that the color and flavor of maple sirup are related to triose sugar {52-5J,, 118-120, 122, 155). These sugars are not constituents of sap when it comes from the tree but are formed as a result of the two reactions shown in chart 14. Evi- dence also indicates that the phenolic ligninlike substances of maple sap are intermediate in the flavor reactions and may account for the speci- ficity of maple flavor (117). The amount of invert hexose sugars is di- rectly proportional to the amount of fermenta- tion that has occurred. The first reaction is the bacterial or enzymatic hydrolysis of the sucrose to form invert sugar, a mixture of fructose and GUUCIC ACID TRIOSE n ACETOL 'Also unpublished data of Eastern Regional Research Center. Chart li. — Chemical reactions showing the formation of trioses from the sucrose of sap. In the first reaction, 1 molecule of sucrose is hydrolyzed by enzymes to yield 2 molecules of hexose sugars. In the second reaction, these hexoses are broken by alkaline fission into trioses. dextrose (chart 14). The second reaction is the alkaline degradation of the fructose and dex- trose to trioses (98). The second reaction occurs while the sap is boiling in the sap pan, where the alkalinity of the sap reaches a pH of 8 to 9. These trioses are highly active chemically. They can combine with themselves to form color compounds, and they can react with other substances in the sap (such as organic acids) to form the maple flavor substances (79). Experiments have established that up to a point the amount of color formed is proportional to the amount of flavor formed. This makes it possible to evaluate flavor in terms of color, a measurable quantity. When the point is reached at which the background flavor "cara- mel" begins to be noticeable, this relation no longer holds. The identity of the compounds responsible for the flavor of maple has proved to be elusive. Certainly all the components of maple sirup 68 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE contribute to its flavor — the sugar, the organ it- acid salts, and even the oil, butter, or whatever was used as an antifoam agent during evapora- tion. An unknown number of trace materials in the sirup or sugar give it "maple flavor." These compounds have defied identification for many years because they exist in very small amounts (a few parts per million), and their chemical character in many cases is so similar to carbo- hydrates that separation from the sugars of the sirup has been extremely difficult (123). Now with the modern techniques of gas chromatog- raphy and mass spectrometry, progress is being made in solving the mystery of "maple flavor." The flavor compounds identified can be divided into two groups according to their probable source. One group, possibly formed from lig- neous material in the sap, contains such com- pounds as vanillin, syringealdehyde, dihydro- coniferyl alcohol, acetovanillone, ethylvanillin. and guaiacyl acetone. A second group, most likely formed by caramelization of the carbohy- drates in the sap, includes acetol, methylcyclo- pentenolone (cyclotene), furfural, hydroxymeth- ylfurfural, isomaltol, and alpha-furonone (25, 116). It has been impossible to make a synthetic maple flavor by combining these compounds. Perhaps one or more key compounds have not yet been identified. Even if all these compounds were available, a proper balance of the many parts of a mixture to give the desired combina- tion flavor would be difficult to achieve since they have not been accurately measured. Factors that control color and flavor are: (1) Amount of fermentation products in the sap (75)\ (2) pH of the boiling sap; (3) concentration of the solids (sugars); (4) time of heating (time necessary to evaporate sap to sirup); and (5) temperature of the boiling sap (la, 150). The two most important factors are the time of heating and the amount of fermentation prod- ucts in the sap (150). The temperature of the sap under atmospheric pressure (open pan) boil- ing is fixed, and nothing can be done about it. Neither can anything be done about changes in pH of the boiling sap. At the beginning of evaporation, the natural acidity of fresh sap is lost and the sap becomes alkaline. It is during this alkaline phase of the pH cycle that hexose sugars, if any are present, undergo alkaline degi-adations. The sap then remains alkaline until sufficient organic acids are formed by the decomposition of the sap sugars to make the sap acid again. The longer the boiling time, the darker the sirup; and, conversely, the shorter the boiling time, the lighter the sirup. During evaporation, the effect of the boiling-point factor increases as the solids concentration of the sap increases. The relation between the amount of hexose sugars (invert sugar) produced during the fer- mentation of the sap and the length of time the sap is boiled is of the greatest importance. Thus, the color and flavor of sirup made in exactly the same boiling time from a series of saps of equal solids concentration (Brix value) but with increasing amounts of invert sugar will be progressively darker and stronger. The stronger maple flavor, however, is usually masked by the acrid caramel flavor. Although flavor and color are formed because of exo- thermic chemical reactions, the amount of fla- vor that can be produced is limited by the concentration of the sap-soluble lignaceouslike materials that are probable flavor precursors. Indications are that there are sufficient of these flavor percursors in sap to permit forming a product that is from 15 to 30 times richer in maple flavor than is commercial "pure maple sirup" (15i). These precursors can be utilized to increase the flavor by subjecting the sirup to higher temperatures. This method is used in preparing high-flavored maple products, de- scribed later. Buddy Sap and Sirup As the maple tree comes out of dormancy, physiological changes in the tree form constitu- ents in the sap which, when boiled, give off a noxious odor and impart a characteristic, un- pleasant flavor to the sirup. This noxious odor is most noticeable in sap obtained from trees whose buds have swelled or burst during a period of warm weather; and sirup made from this sap is said to have buddy flavor. Due to the unseasonably warm weather in 1963, buddy sap was produced early in the sap season. Because of this, much of the crop was not harvested in some areas. Although the trees may not have come far enough out of dormancy to cause the buds to swell, they may have come out enough MAPLE SIRUP PRODUCERS MANUAL 69 to produce the unwanted flavor. The formation of this buddy substance is accompanied by an increase in the free amino acids in the sap. Whether this parallel increase in free amino acids is involved in the foi-mation of buddy flavor remains to be determined. Often some trees in a sugar grove "bud" earlier than the rest. These trees should be identified and marked so that their sap will not be collected late in the season. To combine the sap from trees that have budded with that from the other trees would spoil the entire lot of late- season sap. The practice of treating the taphole with germicidal wllets will cause the sap to flow late in the season and when the tree is far enough out of dormancy so that the sap is buddy. Test for Buddy Fhivor It is essential that sap produced during or following a warm spell or from trees whose buds have swelled be tested for buddiness The best and simplest test is easily performed by bringing V4 cup of the sap or sirup to be tested to a boil and sniffing the steam. If the buddy flavor substances are present, they can be detected in the steam. The sap or sirup can be heated with an electric immersion-type heater used for making instant coffee. This test is subjective, and the buddy odor may not be strong enough to be easily recognized by some people. Another test that is applicable to sirup and not subjective has therefore been developed. This test involves the chemical test for amino acid groups whose presence in sap parallels buddy flavor formation (115). To make the test the following equipment is needed: A 1-ounce (30 ml.) screw-cap bottle to hold the standard amino niti'ogen solution. A box of wooden toothpicks. Test papers — filter paper cut into ^/a- x 4- inch strips. The following reagents should be used: Standard amino nitrogen solution. This is made by dissolving .5 grams of leucine (an amino acid) in 30 milliliters of water. (Place 1 level teaspoon of leucine in the 1- ounce bottle and fill it to the neck with water.) Ninhydrin spray. This is commercially availa- ble as an aerosol spray. The test should be made as follows: (1) To a small volume of the sirup to be te.sted, add an equal volume of water and mix thor- oughly. (2) With a pencil make three dots 1 inch apart down the center of the test strip, 1 inch from either end. Label X, S, and W. (3) Holding a toothpick in a vertical position, dip the broad end into the diluted sirup and transfer a drop to the pencil dot at the top of the paper labeled X. (4) Using fresh toothpicks, transfer a drop of the standard amino nitrogen solution to the dot at the center of the paper labeled S, and a drop of water to the dot at the bottom labeled W. The size of the wetted spots should be about the same. (5) Lay the paper on a clean, diy surface (piece of filter paper) and allow the spots to dry at room temperature. (6) Spray the entire paper strip with the ninhydrin reagent. Wet the paper thoroughly but not enough to cause the reagent to run. (7) Dry the sprayed paper at room tempera- ture. (8) Heat the paper at a temperatui-e of 175° to 195° F. for approximately 1 minute to hasten development of the color. The lid of a boiling kettle or other moderately hot surface will suf- fice. (From 1 to 2 hours will be required for the color to develop at room temperature.) (9) Development of a violet color constitutes a positive test and indicates that the sap is buddy. The standard amino nitrogen solution is used to indicate that the ninhydi-in reagent is react- ing properly to give violet color with amino compounds. Ninhydrin reagent is a very sensitive stain. Care must be taken to keep the paper test strips clean. Handling the test strip with for- ceps, especially after staining, will prevent fin- gerprints which could produce false-colored spots. The papers are best sprayed by hanging them in an open cardboard box to prevent discoloration of other objects by the ninhydrin spray. The ninhydrin i-eagent is not stable and should be replaced at least every 6 months. 70 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Always start with a fresh supply of the reagent at the beginning of each sirup season. Rcrlaiininff Buddy Sirup and Sap Many sirupmakers make buddy sirup from the late runs of sap. Although this practice should not be encouraged because of the very low price commanded by buddy sirup, it is made — often unknowingly. ^ Buddy sap and buddy sirup can be treated by a fermentation procedure to remove their un- palatable flavor {136, 137). Because this process requires special equipment and a high degree of technical conti'ol, it has not been commercially successful. Recently a new procedure has been developed using ion-exchange resins to remove the buddy off- flavor (36a). This process removes the amino acids believed to be responsible for the buddy flavor of maple sirup. The cost of this treatment on a commercial scale is estimated to be less than $1 per gallon of sirup. Riilo of Sirupinakin^ The following rules should be followed in sirupmaking: (1) If possible, test all sap for buddiness; but especially test that produced late in the spring or following a warm spell. Do not use buddy sap. (2) Do not use fermented sap. To keep the sap from fermenting, collect it often. Do not allow it to stand in the buckets or tanks, and keep it cold. If there is a small flow of sap that does not warrant collecting, dump it. At least once dur- ing the season, wash the sap-gathering equip- ment (buckets, pails, and tanks) and sanitize the equipment with a 10-percent hypochlorite solution. (3) Handle the sap as quickly as possible. The sooner sap is evaporated after it has been obtained from the tree, the higher the grade and the lighter the sirup that will be produced. The faster sap is evaporated to sirup, especially during the last stages of evaporation when the solids concentration is highest, the lighter the color and the higher the grade of the sirup. (4) Keep sap and equipment clean. Cleanli- ness is a must in maple sirupmaking for, aside from its esthetic aspects, cleanliness is the only way to control microbial contamination and subsequent growth in the sap. Sirup made from sap in which growth of micro-organisms has occurred tends to be dark colored and low in grade. (5) By means of a hydrometer or other suita- ble instrument, measure and record the sugar content of the sap produced by each tree and also the sugar content of each batch of sap in the storage tanks. (6) Store sap in a cool place. (7) Store sap in tanks exposed to daylight (not necessarily direct sunlight). (8) Cover the tanks with material transparent to ultraviolet radiation, such as clear plastic. (9) Provide tanks having opaque covers with germicidal lamps. Grades of Sirup It is generally believed that the best sirup is made early in the season during the first and second runs of sap. However, this is not neces- sarily true, as was demonstrated in 1954 when sirup made early in the season was darker than some made later. The important factor is the atmospheric temperature. Warm weather favors microbial growth, and the byproduct of this growth — invert sugar — affects the color and grade of the sirup. It is only coincidental that the weather is usually cooler at the beginning of the season and microbial growth is low. Sap that is essentially sterile contains very little invert sugar and will usually produce a light-colored, light-flavored, fancy sirup. Some- times, as in 1954, the weather at the onset of the season is warm, and fermentation occurs. The result is that the first-run sirup is darker than expected. If conditions are reversed later in the season, fancy sirup will be produced, for with cold weather little or no fermentation of the sap occurs. Making light-colored sirup with sterile sap that is veiy low in invert sugar does not test a sirupmaker's skill. However, skill is required to produce light-colored sirup from sap rich in invert sugar (with a high microbial count). This skill is actually a measure of how fast the sirupmaker can evaporate the sap to sirup. Sirup can be darkened — changed from U.S. Fancy to U.S. Grade A, or from U.S. Grade A to U.S. Grade B, etc.— by prolonging the heating MAPLE SIRUP PRODUCERS MANUAL 71 of the finished sirup. If a finishing pan is used, it should be covered immediately when the sirup reaches the correct density. The heat should be reduced to maintain a slow boil until the desired color is obtained. Adding V2 cupful of U.S. Grade C sirup for every 2 gallons of sap will hasten the darkening process. SuiTunar\ (1) Maple sap and sirup contain only sugar, protein, organic acids, ash, and less than 2 percent of material not accounted for but which is of great importance because it includes the color and the flavor substances. (2) Sterile maple sap has neither color nor fla- vor. (3) Experimental evidence indicates that the color and flavor in maple sirup are related to triose sugars, organic acids, and soluble, ligninlike substances. (4) Factors controlling the formation of color and flavor include fermentation, pH, solids concentration, length of boiling time, and the boiling temperature of the sap. (5) The shorter the boiling time, irrespective of the quality of the sap, the lighter the color of sirup produced. (6) For best sirup — (a) Use sap that has not fermented. (b) Use speed in collecting and in evapo- rating the sap. (c) Keep equipment clean. (d) Know the initial Brix value of the sap. (7) Higher grades of sirup are usually produced earlier in the season than later on, because the early season temperatures are usually lower and there is less chance of fermenta- tion. (8) Sirup that is too light can be darkened by heating the finished sirup. CONTROL OF FINISFIED SIRUP Finishing the sirup is one of the most exact- ing tasks in maple sirupmaking. The sirup must be drawn from the evaporator or finishing pan at just the right instant; otherwise, its solids content (density) will be either too high or too low. To conform with minimum Federal and State requirements, sirup must have a density of not less than 66.0° Brix at a temperature of 68° F. At this density, a little more or a little less evaporation has a relatively large effect on the concentration (table 12). Hence, when using large evaporators capable of evaporating sev- eral hundreds of gallons of water per hour, accurate control of the sirup being drawn off is both important and exacting. Viscosity of Maple Sii-up Maple sirup having a density of only 0.5° to 1° Brix below standard-density sirup tastes' thin. This is due to the big change in the viscosity of sugar solutions caused by only a slight change in concentration, especially in the range of standard-density sirup. Table 13 shows that an increase in the sugar concentration of sucrose solutions up to 30° Brix has little effect on viscosity. For example. a solution with a density of 20° Brix at room temperature (68° F.) has a viscosity of 2.3 centi- poises and at 30° Brix only 3.2 centipoises. However, as the concentration of the sugar increases, the viscosity increases at an ex- tremely rapid rate. Thus, to treble the sugar concentration from 20° to 60° Brix increases the viscosity from 2.3 to 44 centipoises — more than a nineteenfold increase. The change in viscosity is even more pro- nounced in sucrose solutions with densities in the range of standard sirup (66.0° Brix). As shown in the table, the viscosity of sirup at room temperature (68° F.) is lowered 34.8 centipoises if its density is 1° Brix below stand- ard density. It is lowered 61.9 centipoises if it is 2° Brix below standard density. The lowered viscosity has a marked adverse effect on the keeping quality of the sirup and on its accept- ance by consumers. The tongue is extremely sensitive to these differences. The tongue is also sensitive to slight in- creases in the density of sirup above 66.0° Brix at room temperature. An increase of only 1° Brix above standard density increases the vis- cosity of sirup 45.8 centipoises; and the sirup acquires a thick, pleasant feel to the tongue. 72 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Table 12. — Boiling temperature above that for water for solutions of different concentrations of sugar Temperature elevation, ° F Sugar solutions Temperature elevation, ° F. Sugar .solutions 0.0 Percent 0.0 7.5 13.8 19.0 23.4 27.1 30.3 33.4 36.0 38.4 40.5 42.5 44.3 46.0 47.7 49.0 50.4 51.6 52.8 53.9 54.9 55.9 56.9 57.8 58.8 5.0 5.2 5.5 5.6 5.8 5.9 . 6.1 . 6.4 . 6.6 . 6.9 . 7.1 . 7.3 . 7.5 . 8.0 . 8.2 . 8.5 . 8.8 . 9.1 _ 9.5 _ 9.9 _ 10.4 _ 10.7 . 11.1 _ 11.5 _ 12.0 _ Percent 59.7 0.2 ^^ 60 4 0.4 61.5 0.6 62 0 0.8 62.5 1.0 62 9 1.2 63.4 1.4 64.4 1.6 64 9 1.8 65 6 2.0 66 0 2.2 66.5 2.4 67 0 2.6 68 0 2.8 68 5 3.0 69 0 3.2 69 5 3.4 70 0 3.6 70.5 3.8 71 0 4.0 71.6 4.2 72 1 4.4 72.5 4.6 73 0 4.8 73 5 Thus, the thicker the sirup, the better it tastes. However, sirup with a density of more than 67° Brix crystallizes on storage at room tempera- ture; 67° Brix, therefore, becomes the upper permissible density. EfTect orTemiMM-atiiiT on N iscosily As the temperature of a sugar solution in- creases, its viscosity drops sharply. Standard- density sirup at its boiling point has a viscosity of about 6 centipoises, which is only one.thir- tieth that of sirup at room temperature; that is why sirup filters so much better when it is at or near its boiling point. Likewise, the viscosity of boiling sirup with a density between 50° and 60° Brix is approximately one-half that of stand- ard-density sirup; and that is why it is advanta- geous to filter sirup just before it is transferred to a finishing pan, when its density is approxi- mately 60° Brix or less. This lowering of the density by heating sirup explains why hot sirup, even though it is of standard density, tastes thin and watery. Old Stan(iar: I'oinI Chart 15 and table 12 show the changes in boiling-point temperature for sugar solutions at different concentrations. When a sugar solution has been evaporated to the concentration of standard-density sirup (66.0° percent of sugar, or 66.0° Brix), its boiling point has been ele- vated 7.1° F. above the boiling point of water. Between 0° and 2T Brix, there is only a slight MAPLE SIRUP PRODUCERS MANUAL 73 0 20 40 60 SUCROSE CONCENTRATION (PERCENT) Chart 15. — Curve showing the relation between the con- centration of a sugar solution (sap) and the elevation of its boiling point above the boiling point of water. elevation in boiling point. However, as the solu- tion neai's the concentration of standard-den- sity sirup, a change of only 2.5 percent in sugar concentration (from 64.5° to 67° Brix) raises the boiling point 1°. Hence, the boiling point method of measuring sugar concentrations is ideally suited to sirupmaking. Any Fahrenheit thermometer calibrated in degree or half-degree intervals and with a range that includes 225° F. can be used. For greatest usefulness and accuracy, the distances between degree lines should be as open as possible and should be calibrated in one-fourth degrees. Elevation of the boiling point as used hei'e means the increase in temperature (° F.) of the boiling point of the sugar solution above the temperature of boiling pure water. It has noth- ing to do with the specific temperatui'e 212° F. except when the barometric pressure is 760 millimeters of merciu'v. Under actual condi- tions of sirupmaking, the barometric pressure is seldom at 760 millimeters; therefore, it is best not to associate the fixed value of 212° F. with the boiling point of water. The recommended procedure is to establish the temperature of boiling water on the day and at the place sirup is being made. To do this, merely heat water to boiling, insert the bulb of a liquid stem thermometer or the stem of a dial thermometer, and note the temperature while the water is actually boiling. This is the true temperature of boiling water for the barometric pressure at that time and place. In practice, the boiling sap in the sap pan can be used to establish the temperature of boiling water since, as was shown in chart 15, at low-solids concentrations (up to 10° BrLx) there is little elevation of the boiling point. The boiling tem- perature of standard-density sirup is then found by adding 7° to the temperature of the boiling sap. It is of the greatest importance to redeter- mine the temperature of boiling water (sap) at least once and preferably several times each day, especially if the barometer is changing. A change in the weather usually indicates a change in barometric pressure. The result of failure to making frequent checks on the boiling point of water is illustrated in the following examples: On March 1, at Gouverneur, N.Y., the boiling point of water was determined to be 210° F., which established the boiling point of standard- density sirup as 217°. On March 2, the producer neglected to redetermine the boiling point of water, assuming it to be unchanged, and con- tinued to use 217" as the boiling point of sirup. Actually, the barometric pressure had fallen, which lowered the boiling point of water to 208° and of standard-density sirup to 215°. The sir- upmaker, by using the temperature of 217°, was boiling his sirup 2° too high, and the sirup contained 69.8 percent of solids instead of 65.8 percent (table 12). This high-density sirup re- sulted in the production of fewer gallons of sirup; and, in addition, the sirup crystallized in storage, since it was above 67° Brix. If, on the other hand, the reverse had oc- curred, the sirupmaker would have made sirup with a boiling point 2° F. too low. This sirup would contain only 59.7 percent of solids as 74 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Table 13. — Viscosity of sucrose solutions of various densities (° Brix) at temperatures of 20° C. (68° F.)tol05° C. {221° F.y I Density solution ;° Brix) Viscosity (centipoises) at — of ( 20° C. (68° F.) 30° C. (86° F.) 40PC. (104; F.) 50° C. (122° F.) 60° C. (140° F.) 70° C. 80° C. (158° F.) (176° F.) 90° C.2 (194° F.) 100° C- 103.5° C.2 105° C.= (212° F.) (218.3° F.) (221° F.) 20 30 2.3 3.2 15.3 44.0 69.2 _ 82.4 . 99.1 . 120.1 _ 147.2 . 182.0 . 227.8 . 288.5 _ 370.1 . 481.6 1.5 2.4 10.1 33.8 39.3 46.0 54.3 64.5 77.3 93.5 114.1 140.7 175.6 221.6 ^1.2 1.8 7.0 21.0 24.1 27.8 32.3 37.7 44.4 52.6 62.9 76.0 92.6 114.0 1.0 1.5 5.0 14.0 15.8 17.9 20.5 23.7 27.5 32.1 37.7 44.7 53.3 64.4 0.8 1.2 3.8 9.7 10.9 12.2 13.8 15.7 17.9 20.6 19.4 22.6 26.3 31.0 0.7 1.0 2.9 7.0 7.6 8.6 9.7 10.9 12.4 14.1 16.1 18.4 21.4 25.0 0.6 .9 2.3 5.2 5.7 6.4 7.1 7.9 8.8 9.9 11.3 12.8 14.7 16.8 50 60 61 62 63 64 65 66 67 1.8 4.4 4.7 5.0 5.6 6.3 7.0 7.8 1.6 3.6 3.8 4.1 4.6 5.1 5.8 6.6 1.5 3.4 3.6 3.9 4.3 4.8 5.4 6.2 1.5 3.4 3.5 3.8 4.2 4.7 5.3 6.1 68 69 70 ' Based on data from Circular C440 issued by the National Bureau of Standards, U.S. Department of Commerce, July 31. 1958. ' Values obtained by extrapolation. sugar. It would not meet specifications for standard-density sirup, would tend to spoil eas- ily, and would have a low viscosity and there- fore would taste watery. Therefore, with a good indicator to detect the end point of evaporation (thermometer cali- brated in V4° F.), together with the slowdown in rate of evaporation, as shown in chart 16, the sirupmaker is able to stop evaporation precisely at the desired concentration. He can do this either by drawing off the sirup from the evapo- rator or, if he uses a finishing pan, by turning off the heat. Finishing Pan When a finishing pan is used, it is necessary to know when the sap has been concentrated enough to be transferred from the evaporator to the finishing pan. This can be determined by measuring the elevation of the boiling point of the partly concentrated sap. Table 12 shows the elevation of the boiling temperature of sugar solutions (above that for water) for concentra- tions from 0° to 73.5° Brix. To use the table, determine the boiling tem- perature of pure water and then observe the boiling temperature of the partly evaporated sap. The difference between the two boiling points represents the elevation in boiling tem- perature. Two examples of how to select a boiling point elevation to give sirup of a desired density (° Brix) follow: Example 1. A producer wants to draw off sirup from the evaporator at about 40° Brix. At what boiling temperature should the sirup be removed if water boils at 210° F.? Table 12 shows that the boiling temperature is elevated 2.0° F. for solutions having a density of 40.5° Brix. Thus, when the boiling tempera- ture rises to 212° F. (210° + 2°), the sap will be concentrated to approximately 40° Brix. Example 2. A producer wants to concentrate the sap to 50° Brix in the evaporator before transferring it to the finishing pan. At what boiling temperature should the sirup be drawn off if water boils at 211.5° F.? Table 12 shows that for solutions having a density of 50.4° Brix, the boiling temperature is 3.2° F. above the boiling point of water. Thus, 211.5° + 3.2°, or 214.7°, is the boiling tempera- ture of 50° Brix sirup. MAPLE SIRUP PRODUCERS MANUAL 75 20 30 40 50 BRIX (DEGREES) Chart 16. — Change in the rate of loss of water by evapora- tion, with constant heat, as the concentration of sap increases. Boiling sap with an initial density of 22° Brix loses 42 grams of water per minute, whereas sirup with a density of 65° loses only 15 grams of water per minute, a threefold decrease in rate. Special Theniionietei*s In sirupmaking, a knowledge of the boiling point of standard-density sirup in ° F. is impor- tant provided a temperature reference point (the boiling point of water) is established and the correct boiling point of sirup is located 7 above it. On this basis, special thermometei's have been developed for use in making sirup: The liquid-stem thermometer with movable tar- get, the liquid-stem industrial thermometer, and the dial thermometer with movable dial. Target Tlierntonieter The target thermometer does not have any markings on the stem. The degree lines on a movable target refer to the boiling point of water rather than to ° F., as on the conven- tional Fahrenheit thermometei-. The target thermometer is calibrated by plac- ing the bulb in either boiling water or boiling sap. The target is moved by means of an adjust- ing screw until the line "water boils" coincides with the top of the mercury column. The line "sirup" is exactly 7° above the line "water boils." This is the boiling point of standard- density sirup for that hour and place. After adjustment, the thermometer is placed in the sirup pan adjacent to the place where the sirup is drawn off. Unfortunately, any thermometer set in the evaporator will be surrounded by steam, which makes it difficult to read (fig. 91). Use of a flashlight' to illuminate the ther- mometer and a large funnel to divert the steam makes viewing easier. The funnel is held with the tip toward the thermometer, and the ther- mometer is viewed through the funnel with the aid of the flashlight. Liqiiitl-Slrm Inthistrial Thcriiiomflfr The liquid-stem industrial thermometer does not have special markings or a movable target. But it does have an open scale — a lineal dis- tance of approximately 3 inches for 10° F., which is almost three times that of other ther- mometers (fig. 92). It is calibrated in hU" and has a magnifying device. These features make it ideal for use in sirupmaking. These thermome- PN-4787 Figure 91.— The target thermometer is placed in the boiling sirup. The fine mercury column is difficult to see because of the steam. The boiling sirup being tested must be deep enough to cover the bulb of the thermom- eter. The thermometer must be in boiling sirup and as close to the point of sirup drawoff as possible. 76 AGRICULTURE HANDBOOK i:{4, U.S. DEPT. OF AGRICULTURE PN-4788 Figure 92. — The liquid-stem industrial thermometer has an open scale that permits calibration marks for each ''4° F. and the temperature of the boiling sirup can be measured precisely. The thermometer is mounted out- side the pan so it is not obscured by steam. It is especially suited when the pan is covered with a tight steam hood. ters can be obtained with the stem bent at right angles and protected with metal armor. The right-angle thermometer is mounted through the wall of the sirup or finishing pan using a special fitting. This arrangement per- mits the thermometer to be mounted high enough on the sidewall of the evaporator or finishing pan to be above the level of the sirup so that the thermometer can be removed for cleaning without loss of sirup. It also locates the scale of the thermometer at an obtuse angle for easy reading. The thermometer is calibrated each day in terms of the boiling point of water. The bulb is immersed in water, the water is brought to a boil, and the temperature is noted. To this observed temperature is added 7°, the tempera- ture elevation required to give the boiling point of standard-density sirup (see table 12). Dial Thermomt'tt'r The degi'ee lines of the dial thermometer (25), like the target thermometer, refer to the boiling point of water (fig. 93). This thermometer has a bimetallic element in the first 3 or 4 inches of the stem. As the indicator is a needle, the openness of scale is governed by the length of the needle and the accuracy required. The scale is twice as open in a dial thermometer 5 inches in diameter as in the target thermometer. The dial thermometer is calibrated by im- mersing the part of its stem that contains the bimetallic element in boiling water or sap the same distance that it is immersed in the sirup; when the indicating needle comes to rest, the dial is rotated by means of an adjusting screw until the zero or water boils line coincides with the pointer. Then the sirup line is located T F. above the zero or water boils line to indicate the boiling temperature of standard-density sirup for that day and place. The long straight stem of this thermometer is inserted through the wall of the sirup pan and sirup drawoff box so it will be parallel to the bottom of the pan and entirely immersed in the boiling sirup. The dial of the thermometer is on the outside of the evaporator where it is out of the steam and is easy to read (fig. 93). Hydixjnietei'S A hydrometer is not the ideal instrument for judging the finishing point of sirup. It is not calibrated for use at the temperature of boiling sirup, and it cannot be used to follow the concentration of the sap continuously. For ac- curacy, the exact temperature of the sirup being tested with the hydrometer must be known so that the necessary corrections can be made. However, the hydrometer and refractom- eter are the only instruments that can be used to measure the density of sirup that is not in an actively boiling state. •Hot Test' The "hot test" is often used to determine whether the process of evaporating sap to sirup is completed. It is made as follows: MAPLE SIRUP PRODUCERS MANUAL 77 PN-4789 Figure 93. — The dial thermometer, like the tai'get ther- mometer, has markings to indicate O, water boils, sirup, soft tub, and cake sugar. The dial thermometer, like the industrial thermometer, is mounted on the outside of the evaporator. PN-4790 Figure 94. — Sirup at approximately 210° F. is used in making the hot test. The hydrometer cup is raised to eye level and the reading is made as soon as the hydrometer comes to rest. Fill the hydrometer cup with boiling sirup from the evaporator or finishing pan (fig. 94). Immediately place the hydrometer in the sirup and, as soon as the hydrometer comes to rest, make the observed density reading. Perform all operations as quickly as possible. If the ob- served hydrometer reading is between 59.3° and 59.6° Brix, the evaporation of the sap to stand- ard-density sirup is completed. For best results with the hot test, the tem- perature of the hot sirup must be between 210° and 218" F. at the moment the hydrometer reading is made. To be sure that the sirup is in this temperature range, first determine the temperature of the hot sirup as follows: Fill the hydrometer cup with boiling sirup. Place the hydrometer and the thermometer in the sirup. Then, instead of i-eading the hydrom- eter, measure the temperature as soon as the hydrometer comes to rest. Repeat this proce- dure and, if the two consecutive temperature readings are not obtained in the range of 210° to 218' F., speed up the operation until these temperatures are obtained at the time hydrom- eter readings are made. The hot test is not a precise measurement. It is extremely difficult to make accurate hydrom- eter and temperature readings at the same time in sirup that is hotter than 180° F. because the sirup is cooling rapidly. Fi-om the time the hydrometer cup is filled with boiling sirup until the observed hydrome- ter reading is made, the sirup will have cooled several degi-ees. The amount of cooling depends on the time involved and the temperature of the air surroimding the hydrometer cup. Hydrothcrin The hydrotherm, a special hydrometer (chart 17), has a liquid thermometer built into it that automatically locates the point on the hydrome- ter (top of thermometer liquid column) for 78 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE measuring standard-density sirup. The accu- racy of this instrument depends on the relation of Uneal expansion of the thermometer Hquid to Hneal displacement of the hydrometer stem by standard-density sirup at different tempera- tures. When used, sufficient time must be al- lowed for the thermometer of the hydrotherm to warm or cool to the temperature of the sirup, usually about 30 to 40 seconds. Since the hydrotherm is not calibrated, the scale does not indicate how much too dense or too thin the sirup is. Suinmarv (1) Finished sirup must contain not less than 66.0 percent of solids (66.0" Brix) at a tem- perature of 68° F. (2) Table sirup that is between 66° and 67° Brix has the best taste. Table sirup that is below standard density tastes thin. (3) Use precision instruments to measure standard-density sirup. (4) The boiling temperature of standard-den- sity sirup is T F. above the temperature of boiling water. (.5) Use a thermometer calibrated in V4° F. to measure the temperature of boiling sirup. (6) Calibrate the thermometer frequently with reference to the boiling point of water. (7) Completely immerse in the boiling water or sap the bulb of the stem of a liquid ther- mometer or that part of the stem of a dial thermometer containing the bimetallic ele- ment. (8) To test hot sirup with a hydrometer, the temperature of the sirup must be noted and necessary temperature corrections applied to the observed hydrometer readings. Hot sirup (210° to 218' F.) of standard density is 59. y to 59.6° Brix. (9) To test hot sirup with a hydrotherm, suffi- cient time must be allowed for the hydro- therm to come to the same temperature as the sirup in which it is floated. STANDARD DENSITY SIRUP THERMOMETER Chart 17. — Hydrotherm for measuring density of sirup. It automatically compensates for temperature correction. (;L\RIFK:ATlo^ ok SIRl I' Snjjar Sainl SirQp as it is drawn from the evaporator contains suspended solids, commonly known as sugar sand. They are primarily the calcium and magnesium salts of malic acid. These salts are precipitated because they become less soluble MAPLE SIRUP PRODUCERS MANUAL 79 as the temperature of the sirup solution in- creases and as its concentration increases. Sugar sand occurs in various forms, ranging from an amorphous black, oily substance to a fine, white, crystalline material. Dark sugar sand will usually cause the sirup to appear a grade or two darker than normal, whereas white sugar sand will often cause it to appear lighter. The amount of this precipitate in the sirup is not always the same. Sap from the same sugar grove varies from year to year and even within the same season. Studies at the Ohio (Wooster) Agricultural Experiment Station' indicate that trees at high elevations tend to produce more sugar sand than do those at lower elevations. The Ohio workers were not able to show any relation between climatological data or soil types and amounts of sugar sand formed. Sirup to be sold for table use must be clear (free of suspended matter) to meet Federal and some State specifications. Sirup can be clarified by sedimention, filtration, or centrifugation. On the farm, sedimentation and filtration are the methods generally used. Sediiiieiitatioii Sedimentation or settling is the simplest method of clarifying maple sirup, but it has several disadvantages. It cannot be used to clarify all sirup. Some sirup contains suspended particles so fine that they resist settling. Clari- fication by sedimentation requires a long time — days and sometimes weeks. After set- tling at room temperature, the sirup must be reheated to 180" F. before packaging to insure a sterile pack. This reheating may darken the sirup enough to lower its grade. To clarify by sedimentation, the hot sirup is first put through a coarse filter, such as several layers of flannel or cheesecloth, to screen out large particles of foreign matter. It is then transferred to the settling tank. The tank should be of noncorrosive metal, and its height should be at least twice its diameter. It should have a dustproof cover and a spigot or other means of drawing off the sirup about 2 inches above the bottom of the tank. The sirup should Unpublished data. be left in the tank until samples that are withdrawn show it to be sparkling clear. It is then drawn from the tank, standardized for density, heated to 180° F., and packaged. Sirup that has failed to clarify after several weeks of standing must be filtered. Because of the un- certainty of the sedimentation method, it is rapidly losing favor. In large operations, the sirup can be kept sterile if it is added to the settling tank while it is hot (above 180° F.) and if the entire surface of the sirup is continuously irradiated by germici- dal lamps. Filtration Filtration of maple sirup is not a simple procedure. As with sedimentation, the success and ease of clarifying sirup by filtration depend on the nature of the suspended particles that are to be removed. It is best to use two filters — a prefilter to remove the coarse material and a thicker filter to remove the fme. In the past, the most commonly used prefilter was several layers of cheesecloth, outing flannel, or similar cloth. Today, a nonwoven rayon material called miracle cloth or maple prefilter paper is used with considerable success. After prefiltering, the sirup is run through a thicker filter. For- merly these filters were made of wool, but now they usually are a layer of synthetic felt (Or- ion). Synthetic felt filters have many advantages over wool felt filters. They do not impart a foreign flavor to the sirup, shrink very little or not at all, do not pill, resist abrasion, stain only slightly, and have a long life. Synthetic filters that have been in use more than 5 years show little evidence of wear. The disadvantage of the two-filter system is that the large particles are removed on the coarse prefilter. The fme particles are collected on the finishing filter, and they may form a compact bed that resists flow of the thick sirup. The most common filtration assembly in the past was a large milk can in which was inserted a cone-shaped, felt bag supported at the top of the can. However, this is little used today. Hat Filters A flat filter consists of a felt sheet for a filtering surface (fig. 95) instead of a cone. It 80 AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE SUGGESTED FILTER TRAYS HEAVY GAGE METAL OR WOOD PN^791 Figure 95. — A simple type of flat filter. A basket of hardware cloth is supported above the two tanks for holding the felt and above this is the support for the prefilter. The prefilter is moved across the tray as new filtering surface is needed. was first used in New York and is gaining in popularity everywhere. The flat filter provides a larger filtering area than does the cone- shaped filter. Distribution of the filter cake over this larger area results in a thiner layer, so the filters can be used for longer periods before cleaning is necessary. The felt sheet is supported in a shallow bas- ket of hardware cloth with 2-inch walls {147). The felt is cut at least 4 inches larger than the bottom of the basket, and the edges are turned up 2 inches to form a shallow tray (chart 18). Usually the felt can be used two or three times longer between cleanings if the sirup is first put through a prefilter. However, because of the physical form of the particles of sugar sand, filtering may be more rapid if the prefilter is not used. This can be determined only by exper- iment. The prefilter is mounted above the felt and is supported on a wire screen basket the same size as that used for the felt (chart 18). The prefilter is cut to fit across the basket, but a length of filter paper is left hanging over the edge of the basket. As the prefilter becomes clogged, a new filtering surface is provided by pulling the prefilter across the basket (fig. 95). The filters can be built in multiples over a common tank (fig. 96). As one becomes clogged with sugar sand, the assembly can be moved to place a clean filter under the spigot. FELT FILTER Chart 18. — Sirup filter. A flat felt filter assembly, con- structed on a milk-can washer that serves as a tempo- rary storage tank from which the hot sirup can be drawn for packaging. Shortening the legs and attach- ing casters or wheels permits the assembly to be moved easily into place under the sirup drawoff spigot. To maintain filtration at a rapid rate the flat prefilters and felts must be cleaned often, espe- cially if the sirup contains a large amount of sugar sand. To clean the filters, the filter cake is first scraped off with a wooden scraper to prevent damage to the filtere. The entrapped sirup is dissolved by dipping the filter into a pan of hot water. The filters are folded with the sugar sand on the inside so that it will not be PX-47y2 Figure 96. — A more elaborate type of installation in which three felt filter units are installed over a com- mon tank. The units are mounted on rollers so that they can be replaced by a fresh unit when necessan,-. The tank is provided with a drawoff valve. MAPLE SIRUP PRODUCERS MANUAL 81 washed into the recovered sirup. The felt is rinsed repeatedly in hot water. The recovered sirup is returned to the evaporator. A homemade washer for flat filters is shown in figure 97. By means of an eccentric, the felt is lifted from the hot water and then dunked repeatedly for 15 to 30 minutes until it is clean. No detergent can be used since it would impart an undesirable flavor to the filter. The felts are then hung on racks to dry or drain. Two or three extra felts are required for replacements while the others are being washed. With an efficient washing machine, the felts can be reconditioned for use so easily that some pro- ducers have discontinued using prefilters. Filtering: Sfiiiiconcenlrtitcd Siriif} When a finishing pan is used, another filter- ing procedure has proved very successful. This procedure takes advantage of these facts: (1) Most of the sugar sand is precipitated (formed) and in suspension when the sap is concentrated to 55° to 60° BrLx, and (2) hot sap at 55° to 60° PN-4793 Figure 97. — A simple type of machine washes flat filters by repeatedly dipping the felts into hot water. Brix has a viscosity of only 1..5° centipoises as compared to 5.4° for standard-density sirup. Therefore, when sap has been concentrated to 55° to 60° Brix, it is filtered as it is being removed from the evaporator and before it is transferred to the finishing pan. In bringing the sirup to standard density in the finishing pan, a small amount of additional sugar sand (precipitate) may be formed. This is easily re- moved by using another felt filter assembly. This final filtration, like all other open filters, permits loss of water as steam that escapes from the hot sirup. This may increase the density of the finished, filtered sirup by as much as 1° Brix. To avoid this, a number of producei-s pump the sirup from the finishing pan through a pipeline to the closed bottling or canning tank. Since this is a closed system, there is no change in the density of the sirup as a result of evaporation. To provide for the final or polishing filtration, an inline, cartridge-type filter is mounted in the pipeline from the finish- ing pan to the holding tank. Two cartridge filters are used, mounted in parallel with sepa- rate control valves so that they can be used alternately. This permits replacing a clogged filter without inteiTupting the sirup finishing and filtering operation. Suiiiinai'v Sedinientdtiott (1) Strain the sirup through a paper prefilter or cheesecloth. (2) Place the sirup in settling tanks. (3) Allow it to stand until all suspended matter has settled out. (Test by periodically draw- ing a small sample from the tank spigot.) (4) Sedimentation is complete when the sirup is ciystal clear as it is drawn off. (5) If the sirup is still cloudy at the end of several weeks, it can be clarified only by filtration. Filtration {Preferred Method) (1) Run the hot, standard-density sirup from the evaporator or finishing tank directly on the filters. (2) Use flat (preferably) filters consisting of a prefilter (paper or flannel) above the felt filter. 82 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE (3) Change the pre filter and the felt filter as often as necessai-y to maintain a rapid rate of filtration. (4) When using a finishing pan, filter the partly evaporated sirup before transferring it to the pan. (5) If a precipitate forms while the sirup is heating in the finishing pan, the sirup must be given a final or polishing filter. (6) Use a closed system in transferring the finished sirup to the holding tank and use an inline, cartridge-type filter for polishing the sirup. CHECKJING AND ADJUSTING DENSITY OF SIRUP The one specification that all gi-ades of table sirup must meet, irrespective of color or other considerations, is density. The minimum allow- able density of maple sirup is 66 percent by weight of soluble solids (66.0° Brix or 35.6° Baume)*' {130a). This corresponds to 11.025 pounds per gallon of 231 cubic inches at 68° F. The density of sirup can be measured in three ways: (1) By weight; (2) by refractometry; and (3) by hydrometry. Vi Method Hydrometry is the most generally used method for measuring the density of cold sirup, ' MAPLE SIRUP PRODUCERS MANUAL 83 PN-4794 Figure 9S. — Checking the density of sirup with a refrac- tometer. Only one drop of sirup is required for this measurement. and it is best suited for use by the sirupmaker. All that is required to make precise density measurements is a relatively inexpensive but accurate hydrometer, a thermometer, and a hydrometer tube or jar (fig. 99). Hydrometry is based on the Archimedes principle that the density of a liquid can be measured by the displacement of a floating body. The hydrome- ter, a partly immersed body, displaces a volume of liquid having a mass equal to the weight of the hydrometer. A hydrometric measurement is made by noting the point on the hydrometer stem that is in contact with the surface of the liquid. The hydrometer must be at rest and floating freely in the liquid, as shown in chart 19. The density value is read from a scale sealed in the stem. The accuracy of a hydrometer measurement depends on the spacing of the markings on the scale in the hydrometer stem, which in turn depends on the diameter of the stem. Thus, the thinner the stem, the farther apart the mark- ings, and the greater the accuracy with which the density measurements can be made. The scale of hydrometers for measuring density of sirup may be marked and calibrated in or on the stem of the hydrometer (chart 20). These scales can be marked by one of three systems or a combination of the systems: (1) Specific grav- ity; (2) Brix scale; or (3) Baume scale. HYDROMETER STEM 7^ READING POINT Chart 19. — Hydrometer used for measuring density. The hydrometer can should be filled to the top. It should be held at eye level for reading. Both specific gravity and the Baume scale relate the weight of a unit volume of maple sirup (the solution being tested) to some other liquid used as a standard; they give no direct information regarding the solids content of the sirup being tested. Brix Sfdif The Brix scale relates the density of sirup to sugar solutions of the same density and known percentages of sugar. The Brix value does not express the true percentage of sugar in a solu- tion containing sugar plus other dissolved sol- ids; rather, it indicates what the percentage of sugar would be if the density of the solution were due only to dissolved sugar. The Brix scale is particularly well suited for measuring the density of maple sirup because 98 percent of the dissolved solids is sugar. For practical pur- poses, the Brix value equals the percentage of sugar in the sirup. 84 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE PN-4796 Figure 99. — A hydrometer is a simple, inexpensive instru- ment for precisely measuring the density (" Brix) of the sirup. The hydrometer should be read at eye level. The temperature of the sirup must be measured and a temperature correction made. A good approximation of the weight of sugar in any lot of maple sirup, whether or not it is standard-density sirup, can be found by multi- plying the weight of the sirup by its density (° Brix) and dividing by 100. This information is important to the producer who sells his sirup wholesale, since the price is based on its solids (sugar) content. Thus, 100 pounds of sirup at 65° Brix contains 65 pounds of sugar, whereas 100 pounds of standard-density sirup (66.0° Brix) contains 66.0 pounds of sugar. Therefore, 100 pounds of the low-density sirup has a lesser value than 100 pounds of standard-density sir- up. Likewise, 100 pounds of sirup with a den- sity of 66.8° Brix contains 66.8 |X)unds of sugar, which is more than that contained in 100 pounds of standard-density sirUp, and it has a greater value. If sirup has an original density of more than 67° Brix, the excess sugar will precipitate out, and the hydrometer will not measure it. To obtain the weight of sugar in sirup when density is measured by a hydrometer whose VT BAUME (eo'F) 25 HYDROMETERS NY BAUME BRIX (68°E) BRIX (ee-E) r~\ 30 35 30 60 61 62 63 64 65 66 -167 J 68 Chart 20. — The three hydrometer scales used in testing sirup. Left, Vermont Baume scale, marked for testing sirup at 60° F.; standard-density sirup at this tempera- ture is indicated by the heavy line at 36°. Center, hydrometer with double scale, marked for testing sirup at 68°; standard-density sirup on the Baume scale of this hydrometer is indicated by the hea\y line at 35.27°. The double scale requires a spindle so large in diameter that accurate readings are difficult to make, since the scale must be compressed, ffi^/if, Brix scale, marked for testing sirup at 68°; standard-density sirup at this temperature is indicated by the heavy line at 65.46°. scale is in specific gi-avity or ° Baume requii-es more involved calculation because neither scale has a direct relation to the amount of sugar present. Baume Scale Even though the Baume scale does not ex- press directly the solids content of maple sirup and its continued use cannot be recommended, its long past use by the maple industry justifies the following explanation and the tabulation on page 85 for the conversion of Baume values (points) to ° Brix. The Baunie scale relates the density of a liquid to that of a salt solution, but it is more MAPLE SIRUP PRODUCERS MANUAL 85 convenient to calculate the Baume value from specific-gravity tables. Thus, " Baume = sp. g. (sp. g.) (M) , where M = the modulus. In the past, unfortunately, neither the tem- perature for which the Baume scale was cali- brated nor M was standardized. Today, M is standardized at 145. The temperature for cali- bration is standardized at 68° F. (except in Ver- mont). In Vermont, the scale is marked at 36° (for use at 60° F.), and standard-density sirup has a Baume reading of 36° when measured at 60° F. In other States and for Federal sjjecifica- tions, the scale is marked at 35.6° (for use at 68° F.). When this scale is used, standard-den- sity sirup has a Baume reading of 35.6° at 68°. When a Baume hydrometer is used, caution must be exercised in observing the temperature at which the scale is to be used. Aleasiirinff Doiisitv Measuring the density of sirup by hydrome- try is relatively simple. Many people, however, incorrectly assume that the observed hydrome- ter reading is the true density of the sirup. This error occurs because they neglect to consider that sirup and sap are water solutions and therefore behave as water does, expanding and contracting with changes in temperature. Most hydrometers and re fracto meters made for use in this country are calibrated for use at 68° F. When used to measure sirup at this temperature, the observed hydrometer or re- fractometer value of the sirup is the true value. If sirup is heated above 68° F., it will expand to a greater volume and its apparent (observed) density will be less than its true density. Like- wise, if sirup is chilled below 68°, it will contract to a smaller volume and its apparent (observed) density will be gi-eater than its true density and corrections must be made. To make exact density measurements, sensi- tive hydrometers that can be read with high precision must be used. The diameter of the hydrometer stem, therefore, must be small enough so that a change in the density of the sap or sirup equivalent to 0.1° Brix will cause an observable change in the depth at which the hydrometer stem floats, as measured at the intersection of the liquid surface and the hy- drometer stem. The hydrometer will have a scale with 0.1° Brix graduations and will usu- ally cover a range of 10° to 12° Brix. The stem will be approximately 6V2 inches long, and the overall length of the hydrometer will be about 13 inches. This type of hydrometer will require a hydrometer cup at least 13 inches deep. Since the Brix scale gives the density of sap or sirup directly in terms of dissolved solids as percentage of sugar, it is ideally suited for use by the maple industry. However, as stated ear- lier, many sirup hydrometers in use today have Baume scales. Baume values (commonly called points) can be converted to Brix values, as follows: Brix Baume Bri,\ Baume Brix 0.0 0.0 0.1 .1 0.2 .1 0.3 .2 0.4 .2 0.5 ..3 0.6 .3 0.7 .4 0.8 .5 0.9 .5 1.0 .6 1.1 .6 1.2 .7 1.3 .7 1.4 .8 1.5 .8 1.6 .9 1.7 1.0 1.8 1.0 1.9 1.1 2.0 1.1 2.1 1.2 2.2 1.2 2.3 1.3 2.4 1.3 2.5 1.4 2.6 1.5 2.7 1.5 2.8 1.6 2.9 1.6 3.0 1.7 3.1 1.7 3.2 1.8 3.3 1.9 3.4 1.9 3.5 2.0 3.6 2.0 3.7 2.1 3.8 2.1 3.9 2.2 4.0 2.2 4.1 2.3 4.2 2.4 4.3 2.4 4.4 2.5 4.5 2.5 4.6 2.6 4.7 2.6 4.8 2.7 4.9 2.7 5.0 2.8 5.1 2.9 5.2 2.9 5.3 3.0 5.4 3.0 5.5 3.1 5.6 3.1 5.7 3.2 5.8 3.2 5.9 .3.3 6.0 3.4 6.5 3.6 7.0 3.9 7.5 4.2 8.0 4.5 8.5 4.7 9.0 5.0 9.5 5.3 10.0 5.6 10.5 5.9 11.0 6.1 11.5 6.4 12.0 6.7 12.5 7.0 13.0 7.2 Baume 13.5 7.5 14.0 7.8 14.5 8.1 15.0 8.3 15.5 8.6 16.0 8.9 16.5 9.2 17.0 9.5 17.5 9.7 18.0 10.0 18.5 10.3 19.0 10.6 19.5 10.8 20.0 11.1 20.5 11.4 21.0 11.7 21.5 11.9 22.0 12.2 22.5 12.5 23.0 12.7 23.5 13.0 24.0 13.3 24.5 13.6 25.0 13.8 25.5 14.1 26.0 14.4 26.5 14.7 27.0 14.9 27.5 15.2 28.0 15.5 28.5 15.8 29.0 16.0 29.5 16.3 30.0 16.6 30.5 16.8 31.0 17.1 31.5 17.4 86 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE Brix ° Baume ° Brix ° Baume " Brix ° Baume Measuring Solids (Content 32.0 17.7 58.0 31.5 64.8 34.9 The effect of temperature on density is more 32.5 17.9 58.5 31.7 64.9 35.0 pronounced in siruD than in sap {H6). Since 33.0 18.2 59.0 32.0 . . ■ ' ^u \.u e u 33.5 18.5 59.5 32.2 65.0 35.0 ^^^"P '^ "'^^^ viscous than sap, the followmg 34.0 18.7 65.1 _ __ 35.1 precautions should be observed: 34.5 19.0 gQQ ^2 5 65.2 35.1 No sirup must be allowed on the part of the 35.0 19.3 gjj J 32.5 -~^^-^ ^^-^ hydrometer stem that is exposed above the 35.5 19.6 gQ2 32.6 ^^■'^ ^^-^ surface of the sirup being tested. The hydrome- 60.3 32.6 • • ter must be clean and dry, and it must be 36 n 19 8 fin 4 "^9 1 oo.b 35. o 365 ' ' 20 1 qp 7 65.7 35.4 inserted with clean fingers. Also, it must not be 37.0 V. ... 2QA 606 32 8 ^^-^ ^^-^ submerged below its floating position and per- 37.5 20.6 60.7 32.9 ^^'^ ^^-^ mitted to rise. The sirup on the exposed stem of 38.0 20.9 60.8 32.9 the hydrometer would add weight, the hydrom- 38.5 21.2 60.9 33.0 ^^'^ ^^-^ 39.0 21.4 60.9 33.0 • • eter would float too deep in the sirup, and the 48.5 26.5 49.0 26.8 66.1 35.6 go g 21 7 66.2 __ 35.7 observed reading would be too low. 4o!o ~ ~- 22^0 ^^'^ ^^'^ 66.3 35.7 Sirup at room temperature is viscous, and 40.5 22.2 „ ■ „ „■ 66.4 35.8 therefore 30 seconds or more will be required 61 3 V 33 2 ^^'^ ^^'^ fo^ ^^^ hydrometer to settle to its point of rest. 41.0 22.5 61.4 33.2 gg",, org If the observed hydrometer readings are made 41.5 22.8 61.5 33.3 gg'g gg^^ too soon, they will be too high. Also, if the 42.0 23.0 61.6 33.3 gg g gg q diameter of the hydrometer cup is too small, or 43 0 23 6 618 33 4 if the hydrometer is floated too close to the wall 43.5 23.8 619 ... 33^5 ^'"^ ^^'^ of the cup, or if the cup is tilted, the movement 44.0 24.1 ^'^■^ 36.1 of i]]Q hydrometer will be restricted and the 44.5 24.4 g2(, gg g 67.2 36.2 observed reading will be incorrect. 45.0 24.6 g2^ gg g ^^-^ ^^-^ rpQ determine accurately the sugar content of • • 62.2 33.6 67.5 36.3 maple sirup, use a hydrometer calibrated in 0.1° 4gjj 62.3 33.7 67.6 36.4 Brix (7.46). Place the sirup in a hydrometer cup 46.5 '/.'".'. 2bA 625 33 8 ^''"^ ^^'^ whose depth is equal to, or slightly greater 47.0 25.7 62^6 33.8 67 9 365 than, the overall length of the hydrometer and 47.5 26.0 g2 7 339 ' ' whose diameter is at least IV2 times larger than '!?■? ??■? 62.8 33.9 ggQ ggg the diameter of the hydrometer bulb. Fill the 62.9 34.0 ;.l 36.6 hydrometer cup to the top with sirup, gently set 495 """"'" 27^^ 68.2 36.7 the hydrometer into the sirup, and allow it to 50.0 27.3 ^^"^ ^^-^ 68.3 36.7 settle unaided until it comes to rest. When the 50.5 27.5 f^\ l^-\ 68.4 36.8 hydrometer comes to rest, at least 30 seconds 63.3 34.2 68.6 36 9 after it IS placed m the cup, carefully hit the 51.0 27.8 63.4 34.2 68.7 36.9 cup SO that the liquid surface is at eye level and 51.5 28.1 63.5 34.3 68.8 37.0 read the mark on the hydrometer scale at the 52.0 28.3 63.6 34.3 68.9 37.0 point of intersection of the hydrometer stem «A fA MS ^11 and the liquid surface (fig. 99). This value is the 53.0 28 9 00.0 o4.4 fiQO '^7 1 <^ n • c \ 53.5 29.1 63.9 34.5 egj gfj observed hydrometer reading ( Brix) of the 54.0 29.4 6a2 __"."'" 37^2 ^irup. 54.5 29.6 64.0 34.5 69.3 37.2 Although most hydrometers are calibrated 55.0 29.9 64.1 34.6 69.4 37.3 for use at 68" F., this does not mean that sirup 55.5 30.2 64.2 34.6 69.5 37.3 ^lust be heated or cooled to 68° before its 56.0 ._.... 30.4 61:4 " - 1^1 Z VZ" 111 density can be measured. Actually, the ob- 56.5 30 7 64 5 34 8 69.8 37 5 served density can be measured at any temper- 57.0 30.9 64.6 34.8 69.9 37.5 ature and the true density, or Brix value, calcu- 57.5 31.2 64.7 34.9 70.0 37.6 lated, if the exact temperature of the sirup at MAPLE SIRUP PRODUCERS MANUAL 87 the time the reading was made is known. The temperature of the sirup should be measured with a pi'ecision Fahrenheit thermometer cali- brated in intervals of 1.0°, or preferably 0.5°. Table 14 shows the amount to be added to or subtracted fi'om the observed Brix reading to obtain the true density of sirup measured at a temperature other than 6S' F. The following examples show how to obtain the true density of sirup in ° Brix: Example 1. What is the true density, in ° Brix, of sirup having an observed density of 65.9° Brix at 165° F.? Since the observed reading is below 69.9° Brix, the correction to use is in column 2 of table 14. Locate the temperature 165° F. in column 1. Opposite this in column 2 is 5.0° Brix, the correction to add to the observed reading. Therefore, the true density of this sirup is 65.9° + 5.0°, or 70.9° Brix. Example 2. What is the true density of sirup having an observed density of 61.0° Brix at 5r F.? Since the observed reading is below 69.9° Brix, the correction to use is in column 2 of table 14. Locate the temperature closest to 57° F. (55° F.) in column 1. Opposite this in column 2 is 0.5° Brix, the correction to subtract from the observed reading. Therefore, the true density of this sirup is 61.0° - 0.5°, or 60.5° Brix. A pearance and create the impression the pack- age is short in weight. Furthermore, air pockets provide a place where the separated mother liquor can collect, and this also produces an unpleasant appearance. Fi-eshly made cream should be packaged im- mediately, before it "sets up" (fig. 110), or within a day if it has been covered and set aside to age. Remelted cream should be packaged while it is still warm and fluid. Since maple cream is a mixture of sugar crystals and satu- rated maple sirup, storing packaged cream at 70° F. or above will cause more sugar to be dissolved. The sirup tends to separate as an unattractive, dark, liquid layer on the surface of the cream. This sirup layer also forms if the cream is stored at fluctuating temperatures. The cream is best stored at low temperature, preferably under refrigeration and at constant humidity. If the cream is packaged in glass or other moistureproof containers, it can be stored in refrigerators for long periods, with little danger of the saturated sirup in the cream separating. Fontlaiit Fondant, a nougat-type candy, is known in Ohio as maple cream because of its very fine crystalline character. Fondant is made in ex- actly the same manner as maple cream except that the sirup is heated to a higher boiling point (27° F. above the boiling point of water). The thickened sirup is cooled to 50° and stirred as for creaming. Since there is less sirup left in the fondant, it will set up to a soft solid at room temperatures. Small amounts can be dropped on marble slab, waxed paper, or a metal sheet; or it can be packed into molds. Sofl Sn^ar ('.an-stallizing sirup and wiped, they are put on wire screen trays and placed in racks for air drying before packaging. MAPLE SIRUP PRODUCERS MANUAL 105 Figure 120. — Packaging sugar candies, a popular confec- tion often used as one of the items in a gift package. the humidity of the room in which they ai'e stored. In a room of low humidity, they will lose moisture. The dried-out areas will appear as white spots and will become stonelike in hard- ness. If the humidity is high, the candies will take up moisture, and moist areas or droplets of water will appear on the surface. The droplets become dilute sugar solutions and are good sites for mold growth. The humidity of the packaging room can be controlled by a de- humidifier and air-conditioner. Never package on rainy days (62). The best type of wrapper for the outside of the candy package is one that is moistureproof, such as metal foil or wax-coated paper. A mois- tureproof wrapper helps to prevent changes in the candies during storage. Unfortunately, most wrappers are not completely moisture- proof.. They reduce the gain or loss of moisture but do not prevent it, especially if the candies are stored under excessively high or low mois- ture conditions or for long jieriods. Some pack- ers of maple confections obtain longer storage by puncturing the moistureproof wi-apper with many small holes to permit the package to breathe. Maple S|u-«'iul Maple cream, described on page 98, is not stable when stored at room temperature be- cause saturated sirup (mother liquor) tends to separate from the cream and cover it with a sirup layer. A new semisolid dextrose-maple spread has been developed that prevents this separation of sirup. Also, it requires no heating or stirring. The process for making the spread consists of three simple steps: (1) The sirup is concentrated by heating it to a density of 70P to 7S Brix; (2) part of the sucrose is converted to invert sugar by enzymatic hydrolysis; and (.3) the dextrose (part of the invert sugar) is ciystallized to form a semisolid spread. Standard-density maple sirup (66° Brix) is heated to about 1(F F. above the boiling point of water (approximately 7(? Brix), and then cooled to 15(F or below (as tested with a thermometer). While the sirup is still fluid, invertase is added at the rate of IV2 ounces per gallon of sirup and thoroughly mixed with the sirup by stiiTing. The enzyme will be inactivated and hence inef- fective if it is added while the sirup is too hot (above 16(F F.). The enzyme-treated sirup is stored at room temperature for 1 or 2 weeks. At first, ci-ystals (sucrose) appear, but they do not form a solid cake, and as the hydrolyzing action of the enzyme progresses, the crystals dissolve. The result is a crystal-free, stable, high-density sirup (70° to 78° Brix) containing a large amount of invert sugar. This sirup will remain clear at ordinary temperatures. Because of its high density, it makes an excellent topping for ice cream and sirup for waffles or pancakes. Maple spread is made by seeding this high- density sirup with dextrose crystals. A crystal- line honey spread, a stock grocery item, is a convenient source of dexti'ose crystals for seed- ing the first batch. For additional batches, crys- tals from previously made lots of the maple spread may be used as seed. The dextrose crystals are added at the rate of 1 teaspoon per gallon of high-density sirup and thoroughly mixed with the sirup. After mixing, the sirup is poured into packages and set aside at a temper- ature of 55° to 60P F. Within a few days a semisolid spread forms. It is stable at tempera- tures up to 8(F F. If refingerated, it will keep indefinitely without any sirup separating. Maple spread eliminates the laborious hand beating or the expensive machine beaters re- quired for making maple cream. Furthermore, the yield of maple spread j^er gallon of sirup is higher, because it is made from sirup concen- trated to between 7(F and 78° Brix, whereas 106 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE sirup for maple cream is concentrated to 8(F Brix. I liin IVoiliirl In making tlie maple products described in the preceding pages, only sirup low in invert sugar should be used, except for that used as a doctor. These products, therefore, are primary uses for the top grades of table sirup, U.S. Grade AA, U.S. Grade A, and U.S. Grade B. A new maple product called fluff has been developed at the Eastern Regional Research Center (135). It can be made from the lower grades of sirup (sirup high in invert sugar). In addition, it has a number of other advantages. Some of these advantages are: (1) There is a large overrun because the volume of the cooked sirup is increased by incorporating air during the beating process; (2) the new product con- tains a higher percentage of water than does maple cream so that a larger volume can be made from 1 gallon of standard-density sirup; (3) the monoglyceride used in the formula tends to reduce its apparent sweetness and make it more palatable, but without loss of the maple flavor; and (4) the time required to whip it is only a fraction of that required for making maple cream. The fluffed product has excellent spreading properties and has an impalpable crystal structure. While there is less tendency for the fluff to bleed, it does tend to become somewhat grainy, especially if stirred too long. This tendency to grain is retarded by storing the fluff under refrigeration. Makhtfi ihf Fluff From Maplf Siriii> Heat the sirup until its temperature has been elevated 17° F. above that of boiling water. Allow it to cool, with occasional stirring, to between 17.5° and 185° F. (as tested with a thermometer). Add highly purified monoglycer- ide (Myverol 18-00)^ equal to 1 percent of the weight of the maple sirup used, that is, 0.11 pound (Va cup) per gallon or 2 level teaspoonfuls per pint. Dissolve the monoglyceride by adding it slowly and stirring. If the sirup cools below 145°, the monoglyceride will not dissolve. Cool to between 150P and 160^ and whip the mixture ' Produced by Distillation Products Industrj'. Roches ter, N.Y. with a high-speed (household) beater. Fluffing should occur within 2 minutes. \hikiiifi thf Fluff From Mofflf .Sin/;* nnti Moith' Sufior To 1 cup of pure maple sirup (any grade) add V2 cup of maple sugar and heat the mixture until the sugar is completely dissolved. Do not boil. Cool to between 175° and 185° F. with occasional stirring. Add slowly and stir until dissolved 1 teaspoonful of Myverol 18-00 for each cup of sirup. Cool to between 15(f and 16(F, and whip the mixture with a high-speed (house- hold) beater. Fluffing should occur within 2 minutes. The sugar must be completely in solution at the time it is whipped to prevent a grainy texture. If sugar crystals do form, they may be redissolved by heating the suspension; but loss of water must be avoided, and no more Myverol need be added. Excessive heating of the Myverol tends to cause it to lose its properties. The texture and consistency of the fluffed products can be varied as follows: (1) Whipping Time. — As time of beating lengthens, the stiffness of the product in- creases. The initial, thin whip can be used as a topping for ice cream or other desserts. The stiffer product is an excellent spread or icing for baked goods. (The beating time will be affected by the temperature of the mixture at the start of the beating. The higher the temperature, the longer it will take to reach a given consistency.) (2) Ratio of Sugar to Wafer.— The higher the sugar content of the mixture in relation to the water content at the time the sugar-water- stabilizer mixture is whipped, the greater the consistency of the fluffed product. Hi^li-Fla>or idly as possible. Steam pressure of from 30 to 1(K) pounds should be used. As soon as the sirup reaches a temperature of 252" F., the steam pressure is reduced until only enough heat is applied to maintain the sirup between 25(P and TRAP DRAIN STEAM OR WATER CONNECTION " Described in U.S. Patent 2,054,873 issued to George S. Whitby on September 22, 1936. This patent has expired, and the process is now available for free use by the public. Chart 22. — Kettle with steam coil can be built in any tin shop. It is not as convenient to use as a tilting-jacketed kettle, but very satisfactory results can be had with it. Like the steam-jacketed kettle it must be operated with high-pressure steam and the condensed water must not be allowed to collect in the coils. Provision should be made for running cold water through the coils for cooling the sirup. 255°. Usually a steam pressure of 20 to 28 pounds is sufficient. A cover is placed over the kettle to prevent further loss of water through evaporation. The cover need not be airtight. Because of the high viscosity of the sirup, little water will be vaporized. A thermometer calibrated in 1° intervals, with a range that includes 250^ to .30(f F., is kept in the sirup during the high-flavoring process. If the temperature of the sirup rises above 255° during the holding period, the steam pressure should be decreased. To prevent for- mation of crystals, the sirup should not be stirred or agitated during the high-flavoring process. The end of the heating (cooking) period is best determined by odor. The cover is lifted, and a handful of steam is scooj^ed up and brought toward the nose; heating is stopped as soon as an acrid caramel odor is detected in the steam. Care must be taken not to get a steam burn. 108 AGRICULTURE HANDBOOK 184. U.S. DEPT. OF AGRICULTURE Always bring the hand to the nose; do not bend over the kettle. At the end of the cooking period, the thick, supersaturated sirup is cooled to I8(f F. Ap- proximately 3 pints of water is added for each gallon of sirup originally used to replace the water lost in evaporation and restore the sirup to standard density. Extreme caution must be exercised in adding the water because the water will be converted to steam with explosive violence if the sirup has not cooled to a temper- ature below the boiling point of water. After addition of the water, the sirup is again brought to a boil and heating is continued until the temperature reaches that of standard-den- sity sirup (7 F. above the boiling point of water). As flavor and color in sirup develop initially to the same degi'ee, flavor development in the treated sirup may be measured indirectly by measuring the increase in its color. A sample of the high-flavored, standard-density sirup is weighed and then diluted with a colorless cane sugar sirup having a density of 66° Brix as measured with a hydrometer or refractometer. The colorless sirup is added slowly to the high- flavored sirup, with thorough stirring, until the mbcture matches the color of the original maple sirup. Then the mixture is weighed. The in- crease in color and flavor is determined by the ratio. Weight of mixed sirup Weight of high-flavored sirup = Increase in flavor This procedure can be used to follow the progi-ess of the high-flavoring process, since different lots of sirup of the same grade develop flavor at slightly different rates. A sample is removed periodically from the cooking sirup and weighed. Enough water is added to restore the sample to standard density (66' BrLx), and its increase in color and flavor is determined. The tests are easy to make; the 2-ounce French squai-e bottle supplied with the U.S. color com- parator (described on p. 89) is used. The high- flavor process and its end uses are shown in figure 121. l'rfssiir<'-( DoLiiifi I'rnifss Many maple producers do not have higli- pressure Steam equipment. They may make A NEW MAPLE PRODUCT ■IJ^ PN"-48n Figure 121.— A schematic drawing showing the high- flavoring process and its use in making blended sirup and as a food flavoring. high-flavored sirup by the pressure-cooking process {139}. In this process, standard-density sirup is heated in a closed vessel, such as an autoclave or ordinaiy pressure cooker, at 15 pounds' pressure. Best results are obtained when the sirup is heated to a temperature of 25(f to 253° F. as in the atmospheric process. In the pressure-cooking process, the water content of the sirup is 34 percent during heating rather than 10 percent, as in the at- mospheric process. The higher water content favors formation of caramel. However, the rate at which caramel forms depends on the original caramel content of the sirup. The higher the caramel content in the original sirup, the greater the amount formed in the product. Since the amount of caramel in sirup is related to the amount of color, only U.S. Grade AA (Fancy) or U.S. Grade A (No. 1) sirup should be used to make high-flavored sirup by the pres- sure-cooking process. Darker grades usually re- sult in an unpalatable product. The sirup is heated almost to boiling and immediately is transferred to jars, which are filled to vvithin '., inch of the top. The lids are MAPLE SIRUP PRODUCERS MANUAL 109 set loosely in place, and the jars are placed in an autoclave or pressure cooker, which contains the amount of water specified by the manufac- turer. The cover of the cooker is assembled, and steam is generated accordinfi: to the manufac- turer's directions. The sirup is heated at 1.5 pounds' pressure for approximately VI., hours. Then the pressure is decreased slowly to zero without venting or quenching. The containers must not be jarred or the sirup may boil over. ( .s«>.s' «»y ftifih-h'hit'ored Siriift High-flavored sirup has a number of uses. Because it is richer in maple flavor, it is ideal for making maple products. It is especially de- sirable for use in making cream and candies. From 1 to 2 percent of invert sugar is formed in the high-flavoring process. This is the optimum amount to make perfect cream or soft sugar candies without the need of a "doctor." High- flavored, high-density maple sirup makes a su- perior topping for ice cream. Only high-flavored sirup should be blended with other foods such as maple-flavored honey and crystalline honey spreads. Regular maple sirup usually does not have enough flavor to compete with or to break through the flavor of the food to which it is added. An inexjjensive table sirup that has the full flavor of pure maple can be made by blending 1 part of high- flavored, standard-density sirup with 3 parts of cane sugar sirup that has a Brix value of 66°. Blended sirup must be projDerly labeled when offered for sale. The percentage of each ingi-edi- ent must appear on the label, with the one in greater amount appearing first. drvslalliiK' Moncv-Miipli- Spix'ad The development of a maple-flavored crystal- line honey spread has produced a new farm outlet for both maple sirup and honey. This spread is made by mixing honey with high- flavored maple sirup {81 ). The maple flavor must be strong enough to break through the honey flavor and tiie siruj) must contain a large amount of invert sugar. These requirements are met by converting U.S. Grade B (Vermont B or New York No. 2) sirup to high-flavoretl sirup as described earlier except that the siruj) is heated to a temperature W or 2(f F. above the boiling point of water. It is then cooled to 150P or lower, and V/., to 2 ounces of the enzyme is added i^er gallon of sirup. The mixture is set aside at room temperature until the action has been completed, usually about 2 weeks. The sirup may have the appearance of soft sugar (U5). The high-flavored, high-density maple sirup is added to mild strained honey at the rate of 33 parts of maple sirup to 67 parts of honey by weight. The mixture is crystallized by the Dyce process (21) as follows: The honey-maple mix- ture is seeded with crystalline honey (available in most gi'ocery stores) or with some honey- maple spread from a previous batch, at the rate of 1 ounce of seed to 1 quart of honey-maple mixture. After thorough stirring, the seeded mixture is held at 57° to BOF F. until crystalliza- tion is complete, usually 3 to 7 days. The result- ing product is smooth, it has a barely percepti- ble gT'ainy character, spreads well, and has a very pleasing flavor. This spread becomes liquid at temperatures above 85°. Therefore, it should be stored under refrigeration. Maple sirup blends well with honey in mak- ing other honey-maple confections. Recipes for these can be obtained from Pennsylvania State University, University Park, Pa. 16802. Other Mapir l*roni Slum- (1) Use the top grades of sirup. (2) Heat the sirup to between 22= and 4(r F. above the boiling point of water. (3) Without stirring, pour the sirup immedi- ately onto the snow or ice; it will form a glassy, taffylike sheet of candy. MAPLE SIRUP PRODUCERS MANUAL TESTING MAPLE SIRl P FOR IINVERT SUGAR 113 The relation between the invert sugar con- tent of maple sirup and its suitability for mak- ing maple cream is as follows: Invert sugar content of sirup (percent) Suitability for cream 0.5 to 2 The right amount of invert sugar for making a fine-textured cream — one that feels smooth to the tongue. 2 to 4 Can be made into cream if sirup is cooked until it is 2° to 4° F. hotter than temperature called for in standard recipes for cream. 4 or more Not suitable for cream. If used, su- crose will not crystallize, or it will crystallize only if sirup is heated to a much higher-than-standard temperature. Such cream will be too fluid and probably will sepa- rate a few days after it is made. Two tests are available for determining the invert sugar content of maple sirup. The simple, or short-cut, test merely shows whether the sirup contains less than 2 percent of invert sugar and is therefore suitable for creaming. The other is a quantitative test. It measures invert sugar in amounts up to 7 percent, the upper limit normally found in maple sirup. Simple Test The simple test for determining the invert sugar content of maple sirup has been adapted from a standard test for determining the sugar in urine (78, 80). The test is made by first preparing a sirup-water mixture (1 part of sirup to 20 parts of water) and then color testing the diluted sirup. It can be made in 3 or 4 minutes. Equipment The few pieces of equipment required to make the tests can be obtained from the local pharmacy. The following items are required: (1) Clinitest tablets'" obtainable at pharmacy. (2) Two medicine droppers. (3) A test tube, about V2 inch in diameter and 3 or 4 inches long. (4) A sample of the sirup to be tested (1 cupful). (5) One medicine glass, calibrated in ounces. (6) One glass measuring cup, calibrated in ounces. (7) Test tube holder. (8) Two 8-ounce, clean and dry drinking glasses. (9) One 1-quart glass fruit jar and cover. (10) One "Clinitest" color scale. (11) Water (20 fluid ounces). M„ki tlu- Test '" Trademark. This product is one of several that may be used by diabetics in testing for sugar in urine. (1) Carefully pour enough of the test sirup into a medicine glass to bring the level of the sirup exactly to the 1-ounce (2 tablespoons) mark. If too much (more than 1 ounce) is added, empty the sirup out of the medicine glass, wash and dry it, and start over. (2) Measure 2V2 cups of water and transfer it to the quart jar. (3) Make the l-to-20 solution by pouring the fluid ounce of sirup into the jar containing the 2V2 cups (20 fluid ounces) of water. (4) Pour some of the water-sirup mixture into the medicine glass and return it to the jar. Repeat this three or four times to be sure that all the sirup has been transferred to the water in the jar. Mix the contents of the jar thor- oughly by stirring with a spoon or with a portable electric mixer. (5) Place the test tube upright in the holder. (The holder can be a 1-inch-thick block of wood, 2 inches square with a ''/le-inch hole ^/4 inch deep.) (6) Fill a clean, diy medicine dropper with the diluted (1:20) sirup in the fruit jar. Hold the dropper upright above the test tube and let 5 drops of the diluted sirup fall into the test tube. (7) Fill another clean and dry medicine drop- per with water and add 10 drops of water to the test tube. (8) Place a Clinitest tablet, freshly removed ft'om the bottle or wrapjier, in the test tube. As the tablet dissolves, it causes the contents of the tube to boil. Do not remove the tube from . the holder while the solution is boiling. 114 AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE (9) Fifteen seconds after the boiling stops, add water to the test tube until it is two-thirds filled. (10) Observe the color of the solution and compare it with the two colors marked + and - of the color scale furnished with the Clinitest tablets. Disregard everything else on the scale card. The other colors and the" labels on the scale card have no relation to this test. Make the color comparison in a room illuminated with an incandescent bulb. The colors are not easily judged by fluorescent or direct sunlight. Intvritretinfi the Krsiills Color of Solution in Test lube. — Blue indi- cates a negative test; the sirup contains less than 2 percent of invert sugar and can be used to make cream. Yellow or yellow gi-een indi- cates a positive test; the sirup contains more than 3 percent of invert sugar and is not suita- ble for making cream. Quantitative Test The quantitative test is much longer than the simple test; it requires about 15 minutes. I'rpparing the Siriiit-Wtiter Mixtures For this step, you will need sirup, 15 quarts of water, measuring cup, quart measure, pail or other large container, long-handled spoon, small spoon, and five 4-ounce drinking glasses. The glasses should be thoroughly dry. You will also need a pencil and labels. Stir thoroughly the sirup to be tested. Then fill the measuring cup exactly to the 1-cup mark with sirup. Dilute this sirup with five successive addi- tions of water, as follows: l-and-1'2 Dilutimi (1 cup of sirup and 12 cups of water). — Pour 2 measured quarts (8 cups) of water into the pail. Pour the cupful of sirup into the pail; let the cup drain until most of the sirup is out of the cup. Measure a third quart (4 cups) of water and use this to rinse the remaining sirup from the cup; fill the cup with water, stir with a small spoon, and pour into the pail until the quart of water is used. Stir the sirup and water in the pail until it is thoroughly mixed. Dip one 4-ounce glass into the dilute sirup and withdraw half a glassful. Label the glass "12" and set it aside. l-and-20 Dilution. — To the dilute sirup in the pail, add 2 measured quarts (8 cups) of water. Stir tlie contents of the pail until well mixed. Remove half a glassful and label it "20." l-and-32 Dilution. — Add 3 measured quarts (12 cups) of water to the mixing pail. Stir contents until well mixed. Remove half a glass- ful and label it "32." l-and-40 Dilution. — Add 2 measured quarts (8 cups) of water to the pail. Stir contents until well mixed. Remove half a glassful and label it "40." l-and-60 Dilution. — Add 5 measured quarts (20 cups) of water to the pail. Stir contents until well mixed. Remove half a glassful and label it "60." Color Tesliiifi the Dihitioiis For this step you will need the labeled sam- ples of the five dilutions, test tube holder for five tubes, five test tubes, six medicine drop- pers, Clinitest tablets and color scale, a small amount of water, and pencil and paper. Make the color test as follows: (1) Place five of the test tubes in the test tube holder. (2) Fill a clean, diy medicine dropper with the diluted sirup from the glass labeled "60." Hold this dropper upright above the test tube in the hole marked "60" and let exactly five drops of the diluted sirup fall into the test tube. Similarly, place exactly five drops of the "40" dilution, five drops of the "32" dilution, five drops of the "20" dilution, and five drops of the "12" dilution in the tubes numbered for these dilutions (see fig. 123). Use a separate, clean, dry medicine dropper for each dilution. (.3) Fill another clean medicine dropper with water and add 10 drops of water to each of the five test tubes, refilling the medicine dropi^er as necessary. (4) Remove five Clinitest tablets from the bottle or wrapper. Place them on a clean piece of paper. (5) Place one tablet in each test tube, in order, starting with the tube marked "60." The tablets, as they dissolve, cause the con- tents of the tubes to boil. Do not move the test tubes while tlie solutions are boiling. MAPLE SIRUP PRODUCERS MANUAL 115 Figure 123. PN-1S19 -Testing sirup for invert sugar. Write down in order the values you have griven the five dilutions, starting with the 1-and- 12 dilution at the left. Special Note. — If the first sirup you test proves positive in some dilutions and negative in others, you will quickly see the difference between a positive and a negative color reac- tion. It is possible, however, that the sirup you test will give a positive or a negative test in all dilutions. If this happens and you ai'e doubtful about your interpretation of the results, it will be helpful to have a solution that you know will give a jx)sitive test. To prepare such a solution, add three drops of corn sirup to the 4-ounce glass containing the sample of the l-and-60 dilution. Stir the com sirup into the dilute sirup. In a clean test tube place five drops of this solution. Add 10 drops of water, then one Clini- test tablet. After boiling has stopped add water until the test tube is two-thirds full. The color that develops will indicate a posi- tive reaction. (6) Fifteen seconds after the boiling stops, add water to the test tube marked "60" imtil the tube is two-thirds full. Add the same amount of water to the other four test tubes, in order, from right to left. (7) Compare the colors in the test tubes with the two colors of the color scale marked "trace" and "-f^". Disregard everything else on the scale; the other colors and the labels on all the colors have no relation to this test. Make this comparison in a room lighted with an incandescent bulb. You cannot judge the colors of the solutions for this test with fluores- cent light or with sunlight only. Assign to the mixture in each tube one of three values — positive (+ ) for invert sugar, neg- ative (-) for invert sugar, or doubtful (±) ac- cording to the following standard: Color of solution Value Same as or more blue than color on scale labeled "trace" Negative (-) Same as or more yellow than color on scale labeled " + " Positive ( + ) Between "trace" and " + " colors on scale Doubtful (± ) Detorniiiiiiig In>ei't Siiftar Content of Sirup To find the invert sugar content of the sirup you are testing, find the line in table 17 that contains the same combination of values for the five dilutions that you obtained in the color test. As the table shows, the sirups that are most suitable for making into cream are those that are negative in all dilutions or positive in the first (l-and-12) dilution and negative in all the others. Suniniaiy (1) Test the sirup for its invert sugar content before attempting to make maple cream. (2) Use the simple or shortcut test, page 113. (3) To check the color, positive or negative, use a test .solution consisting of the 1- and 60- solution to which is added com sirup, page 115. This will give a positive test. (4) Sirup containing more than 3 percent of invert sugar is unsuitable for creaming. 116 AGRICULTURE HANDBOOK l.'?4. U.S. DEPT. OF AGRICULTURE Table 17. — Key for interpretinx) results of color test for invert siigar content of five dilutions of maple sirup [- indicates negative reaction; + indicates positive reaction; ♦ indicates doiibtlul reaction! Reactions for 5 test dilutions Invert-sugar content of sirup Suitability of sirup for making into cream Percent Less than 2 Suitable. More than 2, less than 3 Suitable. More than 2, less than 4 Suitable if sirup is heated 2 to 4 degrees higher than usual in cream- making. More than 3, less than 4 Not suitable. More than 3, less than 5 Not suitable. More than 4, less than 5 Not suitable. More than 4, less than 6 Not suitable. More than 5, less than 6 Not suitable. More than 5, less than 7 Not suitable. Above 6, may be 7 or more Not suitable. THE CErNTRAL EVAPORATOR I'LAINT Before 1955 no market existed for maple sap. The sap crop had to be converted to sirup or some other product on the farm where it was produced before it became marketable. Maple sap, therefore, occupied a unique position in American agriculture because all other farm crops are marketable as produced. This practice contributed little toward devel- oping the maple industry or toward moderniz- ing sap production to make it competitive with dairying, stock raising, or gi-ain farming. The cuiTent trend toward central evaporator plants (figs. 124 and 125) has marked a new era in the maple industry. No longer do all sap producers have to be skilled sirupmakers; in- stead, the central plants are operated by and staffed with specialists not only in sirupmaking but also in marketing. Other advantages of- fered by the central evaporator plants are: (1) The central plant eliminates the former duplication on each farm of invested capital for evaporator and related equipment and for an evaporator house. (2) The farm plant often was too small to be operated economically and was wasteful of la- bor. A small evaporator having an output ca- pacity of 1 to 5 gallons of sirup per hour re- quires as many man-hours for its operation as does the central evaporator plant that produces 15 or more gallons of sirup per hour. (3) Thousands of farmers with stands of ma- ple trees that they had not previously used for sap-sirup production now find it practical and economical to produce and sell a sap crop. (4) A more uniform and better quality prod- uct can be produced in a central plant. This tends to stabilize the market. PN-1S20 Figure liJ,. — This central evaporator plant at Ogema, Wis., has one evaporator. MAPLE SIRUP PRODUCERS MANUAL 117 Figure 125. — A large central evaporator plant located at Anawa, Wis. Some plants are large enough to make 20 or more gallons of sirup per hour. L«>4-atioii The site for a central plant should be cai-e- fully chosen. Some of the factors to be consid- ered are: (1) It should be centrally located in relation to the sap-producing farms. (2) It should be on an improved road, prefera- bly at an intersection. The road should bear considerable nonlocal traffic. (3) It should have adequate space for drive- ways for delivery of sap. (4) It should have an access roadway from the main road and off-road parking areas for visi- tors (customers). Size Like other industries, the size of the central evaporator plant will be governed by a number of factors that can readily be determined. Un- like other industries, the central plant can eas- ily be expanded to accommodate increased de- mands because of the relative simplicity of equipment and plant design. The initial plant must be large enough so that the volume of sirup produced will yield reasonable returns on the invested capital and so that labor will be used economically. These two factors will be determined by the cost of the sap, the number of hours per day the plant is operated and the length of the season, the number of man-hours required to operate the plant, the output, and the price of the finished product. These factors, in turn, depend on the size of the evajwrators, the density f Brix) of the sap, and the efficiency of the plant. Since the plant handles liquids (sap and sir- up), it can be completely automated. The extent of automation will be governed by the size of the i)lant and the budget. The cost of producing a gallon of sirup decreases as plant size in- creases. An evaporator plant building of shed roof design permits easy expansion. The shed roof building can be doubled in size by adding three walls to convert it to a gabled roof building. The building must be large enough to permit easy access to the evaporators and other equipment. The materials should be easy to clean, such as concrete floors, smooth walls, and built-in cup- boards and resti-ooms. Provision should be made for a candy kitchen and a salesroom. The most common type of central evaporator plant uses oil heat to evaporate the sap in tlue pans, each of which is independently installed on its own arch with its own oil burner (see p. 59). A coil or tube of high-pressure steam is used to heat the finishing pan, which is also mounted on its own support (fig. 126 and chart 23). PN-1822 Figure 126. — Interior of a modern central evaporator plant at Bainbridge, N.Y. Oil heat is used to evaporate the sap in the four flue pans and high-pressure steam is used at the finishing stage. 118 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE CENTRAL SAP EVAPORATOR PLANT Chart 23. — Flow diagram: Oil-and-steani plant. Coal is used in some areas, particularly where it is cheap. It is best used to generate high-pressure steam which, in turn, is used to evaporate the sap (fig. 127). As with oil-fired evaporators, a series of pans is used. These pans, like the oil-fii-ed pans, are mounted stepwise, as shown in figure 128. The pans are heated with 80 to 110 p.s.i.g. steam in coils or manifolds of ^/4-inch brass tubing mounted at the bottom of the flat pans. The specifications for a small plant (about 8,800 gal. per season) described by Pasto and Taylor {86) are as follows: Sap gallons per hour. Water evaporated do Sirup produced do Tapholes number.,. Fuel consumption gallons Capital investment dollars. _. Floorspace square feet Sap storage gallons... Density of sap at — 1.6° 2.4° Brix Brix 807 815 792 792 14.7 22.2 32,000 32,000 23,800 23,800 25,291 25,291 1,226 1,226 20,000 20,000 Capital investment and cost for depreciation and repairs for a small plant, as reported by Pasto and Taylor {86), are given in table 18. Smaller plants are in operation and are prov- ing highly successful. Usually these plants are small initially, but they are built so that they can be enlarged after 2 or 3 years' operation. Typical of these is the central evaporator plant established in 1962 at Ogema, Wis. (fig. 124). This plant has one 6- x 20-foot evaporator and a separate finishing pan. Sap is supplied from 9,500 tapholes on 16 farms. Operation The sap supplied to the evaporator from the storage tanks is fed to the first flue pan. Since the flue pans are connected in series, the sap flows successively through each pan to the next. The sap is conducted between pans through large-diameter, heat-resistant tubes or pipe at least IV2 inches in diameter. The pans can be installed in a stepwise manner to insure no backward flow of sap from pans of higher concentration to pans of lower concentration and to better control the depth of the liquid level in each pan. Since the elevation between pans is only 6 to 8 inches, there is only a small hydrostatic pressure in each interconnecting feed line. Feed lines and valves must be large enough to supply sap to the pans rapidly enough under this low pressure to replace the vast quantities of water being removed by evaporation. The liquid level in the evaporator pans is maintained at a fixed depth by means of a mechanical float valve or by an electrically operated liquid level sensing element and sole- noid valve. Whichever mechanism is used, it must be sensitive to minute changes in liquid level and must operate instantaneously. In principle, when the finishing pan requires more liquid to maintain its depth of sap, the sap is obtained from the third pan of a 3-flue pan installation, which in turn obtains more sap from the second pan, and so on back to the storage tank. The sirup is removed from the finishing pan when it reaches standard density (66.(f Brix) or slightly higher. The operation can be automated by use of a thermoswitch and solenoid valve. The thermo- switch is adjusted to open the valve when the MAPLE SIRUP PRODUCERS MANUAL 119 boiling sirup reaches the desired temperature above that for boiling water at that location. The operation is not completely automatic, since the thermoswitch must be handset as PN-)K23 Figure 127.— Where coal is inexpensive, high-pressure steam boilers may be used to evaporate sap to sirup. PN-4824 Figure i2^. — Interior of a multiple-pan, all-steam central evaporator plant at Stoystown, Pa. many as three or four times a day to compen- sate for fluctuations in barometric pressure. The U.S. Department of Agriculture has devel- oped a new controller that will automatically compensate for changes in the boiling point of water due to changes in barometric pressure (15). In some installations, the partly concentrated sirup is not supplied to the finishing pan by gravity feed. Instead, an electric pump, acti- vated by an electrically operated liquid level sensing device in the finishing pan, removes the sap from the last flue pan or semifinishing pan when it reaches the desired concentration — any point between 2(f and 60? Brbc. If the Brix value of the sirup supplied to the finishing pan is above 5(f , essentially all of the sugar sand will have been formed and will be in suspension. Its viscosity will be very low (see table 13). It is advantageously filtered at this point. The filtered sirup is then pumped into the finishing pan. When it reaches the desired density, it is automatically drawn by means of solenoid valves and thermoswitch, and piped to the holding or canning supply tank. With this procedure, little or no sugar sand is formed in the finishing pan. A cartridge-type filter can be installed in this line to iwlish the sirup (that is, remove the cloudlike precipitated sugar sand). If the sirup is not prefiltered, it can be piped from the finishing pan to a pressure filter such as a plate-and-frame type and then to the holding tank. Either method is desirable, since once the sirup reaches standard density, it is kept in a closed system so that it cannot evapo- rate further. To reduce holdup time, it is good practice to keep the liquid level as low as possible in each evaporator. There is, of course, always a danger that because of some failure, insufficient liquid will be fed to each pan and the pan will be ruined by burning. This can be prevented by connecting a hose to the raw-sap feed line by which sap can be added quickly to any location in any one of the pans. Although a gas-fired finishing pan is satisfac- tory for smaller plants, it is advisable to use high-pressure steam for the finishing pan in plants that make as much as 15 gallons of sirup per hour. The steam permits finishing the sirup without danger of burning it. The steam is best 120 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE supplied from an automatically operated, liijjh- pressui-e boiler (80 to 110 p.s.i. and a rated horse- I)ower of 20 or more). If no prefilti'ation or inline cartridg:e filters are used, the finished sirup can be efficiently and economically filtered immediately after it is drawn from the evaporator. A battery of three or more open, flat, felt filtei's stsould be used. Allowance must be made for loss of water as steam while the sirup is being filtered. This loss tends to raise the Brix value of the sirup approximately Y . S;i|> .S|||»|>|i4-|-s Sap can be obtained in any one of three ways: (1) It can be obtained from rented trees; (2) it Table 18. — Capital investment in plant and equipment and cost of depreciation and repairs for small oil-and-steam type plant ' Life length Yearly depreciation Yearly repairs Dollars Land (1 acre at $200) 200.00 Roadway, ramps, grading Building (1,226 sq. ft. at $4 per sq. ft.) Equipment and other items: Sap-receiving tanks (19,495 gal. at $0.08,3 per gal.) Germicidal lamps for sap receiving tanks (12 at $25) Pump for sap Sap filter Flue-type sap evaporators (4 at $650) Arches for sap evaporators (4 at $287) Covers and stacks for sap evaporators (4 at $160) Steam semifinishing evaporator, size 5 x 6 ft Cover and stack for semifinishing evaporator Steam finishing evaporators and coils (2 at $100) Hoods and stacks for finishing evaporators Float valves (5 at $5) Oil burners (4 at $332) Smokestacks (4 base stacks at $31; 4 top stacks at $57) Finishing filter (2 at $14.70) pressure cartridge Finished sirup holding tank with heating device Finshed sirup storage tank (3,940 gal. at $0.25 per gal.) __ Steam boiler (20 h.p.), installed Oil tank (8,000 gal.) Automatic sirup drawoff Gravity filter Pumps and motors to filter and to finishing evaporators (2 units at $75) Can filling equipment Thermometers (2 at $50) Testing equipment ( re fracto meter, $100; hydrometer, $48; scales, $150; thermometers, $10) Portable power-stirring device Water supply (well) plumbing, sink Restroom furnishings Office equipment Other installation charges (burners, tanks, pumps, etc., besides cost of equipment) Miscellaneous Total ' About 8,800 gal. per year. 1962 dollars. Source: Pasto and Taylor («6). Dollars 500.00 20 22.50 15.00 4,904.00 30 147.12 147.12 1,618.08 20 72.81 48.54 300.00 10 27.00 9.00 150.00 10 13.50 4.50 50.00 10 4.50 1.50 2.600.00 10 189.00 63.00 1,148.00 10 103.32 34.44 640.00 10 57.60 19.20 138.00 10 12.42 4.14 108.00 10 9.72 3.24 200.00 10 18.00 6.00 100.00 10 9.00 3.00 25.00 10 2.25 .75 1,328.00 10 119.52 39.84 352.00 10 31.68 10.56 29.40 10 2.29 .76 75.00 10 6.75 2.25 985.00 20 44.32 29.55 4,485.00 20 201.83 134.55 1,000.00 20 45.00 30.00 100.00 10 9.00 3.00 140.00 10 12.60 4.20 150.00 10 13.50 4.50 50.00 10 4.50 1.50 100.00 10 9.00 3.00 308.00 10 27.72 9.24 300.00 10 27.00 9.00 1,000.00 20 45.00 30.00 500.00 30 15.00 15.00 500.00 10 45.00 15.00 912.00 10 82.08 27.36 800.00 10 72.00 24.00 25.791.48 1,502.,53 7.52.74 MAPLE SIRUP PRODUCERS MANUAL 121 can be picked up at the farm; or (3) it can be delivered to the plant (figs. 129 and 130). The quality of sap is not easy to judge by visual inspection. But the buyer must guard against purchasing spoiled or unsound sap, since a small amount could contaminate a large amount of sound sap when added to it. The plant operator must therefore exercise some control over the production of sap by the sap suppliers. He therefore should set certain mini- mum standards. I'rotliirtioii Stdmlards for Sa/t I'.ollevted in Buckets (1) All buckets must be covered. (2) Buckets must be clean and sanitized be- fore use. (3) In midseason or after a warm period, buckets must be washed again. (4) Collecting buckets and tanks must be kept clean and sanitized. (5) Sap (even a very small amount) that has remained in buckets between runs must be discarded. Production Standards for Sfip Collected in Plastic Tubinfi (1) Only clean tubing must be installed. (2) All collecting or venting equipment must be washed and sanitized. Standards for Slorti^e Tanks on Sti/t harms (1) All tanks must be washed and sanitized before the start of the sap season. (2) Tanks must be completely emptied, washed, and sanitized at least twice each sea- son and preferably between each run of sap. PN-ia2.s Figure 129. — Sap i.'i delivered to a central evaporator plant in a variety of vehicles. These vehicles are waiting; to unload. PN-4826 Figure 130. — Sap is delivered in all types of containers (including- milk cans) and by eveiy available type of conveyance ranging from the trunks of passenger cars to trailers drawn by farm tractors. Pi-oduction of a darker grade of sirup indicates that the tank needs washing and sanitizing. (3) Tanks should be covered with clear, trans- parent plastic that transmits the sanitizing ultraviolet radiation of sunlight. (4) Tanks must be constructed with smooth, easily cleaned surfaces. Metal tanks best meet the requirements. l*iirohafi«' of Sap Sap is bought on the basis of the total weight of solids (sugar) it contains. It is necessary to measure with precision the volume of the sap to the nearest gallon, its density to the nearest 0.1° Brix, and its temperature to the nearest ° F. The volume of sap can be determined in several ways, as follows: (1) By means of a meter through which the sap can be pumped or can flow by gravity. This is the most precise and direct method, provided the meter is calibrated carefully and is checked frequently. Be sure the meter is designed for operation at low pressures. 122 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE (2) By use of tanks of standard sizes cali- brated in gallons for different depths of liquid. The calibrations are usually made on a "dip stick" calibrated for a specific tank size. The stick is lowered vertically to the bottom of the tank and the heipfht of the sap in the tank is noted by the wet line on the stick. This line indicates the depth and volurne of the sap. Usually, when sap is delivered to the plant, it is run into a receiving tank that can be calibrated precisely. The calibrations should be accurate to ± 1 gallon. (3) By its weight. The tank of sap is weighed before and after emptying. The empty (tare) weight is subtracted from the weight of the tank and sap to obtain the weight of sap. The weight of sap is divided by 8.39 (the weight of 1 gallon of sap). The only tangible constituent of sap that can be used to establish its price is its solids con- tent, which is measured and expressed as ° Brix. This measurement is made at the plant by using a quart sample taken when the sap was picked up at the farm or when it was delivered to the central plant (fig. 131). The sample identified with supplier's name and date can be stored a few hours before determining its Brix value. Or its Brix value can be deter- mined at the time the sap is picked up or delivered provided its temperature is also deter- mined at that time. The observed Brix value of the sap is the value read to the nearest 0.1° from the test instrument (hydrometer or refractometer); this value, together with the measured temperature of the sap, is recorded. From these, the true Brix value of the sap is calculated. Corrections to be applied to the observed Brix value to obtain the true Brix value of saps of various temperatures are as follows: Temperature of sap, ° F. 32-42 43-53 54-62 63-66 Correction to subtract from observed Brix value CBrix) 0.4 .3 .2 .1 The value of sap is not constant but varies with its solids content (percentage of sugar), or Brix value. The higher the Brix value, the smaller the amount of sap required to produce 1 gallon of sirup. Less water has to be evapo- rated, less volume is handled, and less storage space is required. Sap with the highest Brix reading therefore has the highest value. The base price for sap is usually for sap of 2" Brix. This base price is determined by a num- ber of factors, the most important of which is the price of the finished sirup. For sirup selling at $9 to $12 a gallon, one New York producer reported in the National Maple Syi-up Digest (1) the following prices paid for sap delivered at the evaporator plant in 1974. The prices can be adjusted up or down by such factors as effi- ciency of the plant, hours of operation, and wage scales. True Brix value of sap ' 1.5° 1.6° 1.7° 1.8° 1.9° 2.0° 2.1° 2.2° 2.3° 2.4° 2.5° 2.6° 2.7° 2.8° 2.9° 3.0° 3.1° 3.2° 3.3° 3.4° 3.5° 3.6° 3.r 3.8° 3.9° 4.0° Price per gallon (cents) 2.9 3.9 4.9 5.8 6.6 7.3 7.9 8.5 9.1 9.7 10.2 10.7 11.2 11.7 12.2 12.7 13.2 13.7 14.2 14.7 15.2 15.7 16.2 16.7 17.2 17.7 ' True Brix value is the observed Brix reading corrected for temperature. Storing Sap The central evaporator plant must provide facilities to store a full day's production of sap. There is no precise means for estimating the size. However, experience has shown that on days when sap flows well, ft'om 4,000 to 20,000 gallons will be produced per 10,000 tapholes. Thus, a plant having a capacity of 8,800 gallons MAPLE SIRUP PRODUCERS MANUAL 123 PN-4827 Figure 131. — A sample of sap is taken for determining its Brix value and for judging its quality. The observed Brix value, temperature, and volume of the sap are recorded for each delivery. of sirup annually would I'equire sap from 10,000 to 35,000 tapholes, or 70,000 gallons of sap per day. Since the plant would be operating contin- uously after the first delivery of sap, the re- quired storage facilities would be somewhat less than the daily requirement of sap. Storage tanks can be made of several mate- rials and in several shapes. Metal-lined tanks are preferred because their surfaces are smooth, easily cleaned, and sanitary. Concrete tanks are the most difficult to keep clean be- cause droplets of sap, in which micro-organisms can gi'ow, can lodge in the rough surfaces. Concrete walls can be made smooth with differ- ent types of coatings; however, before the walls are coated, clearance for the use of the particu- lar coating should be obtained from State and Federal food agencies. Plastic tank liners also have been used successfully, especially in wooden tanks. The storage tanks should be located in a cool place. Aboveground storage is preferable be- cause of ease in making repairs and cleaning. All tanks must be covered- If the tanks are not equipped with germicidal lamps, they should have transparent plastic covers and should be located to receive as much sunlight as |X)ssible. Because of the depth of the sap in the tanks, the efficiency of daylight sterilization is low. It is recommended that germicidal lamps be used. One or more lamps should be arranged to illu- minate the entire surface of the sap. The lamp fixture should be provided with a bright metal reflector so that most of the ultraviolet radia- tion will be used. These lamps are also effective in sanitizing empty or partly empty tanks, pro- vided no buildup of foam or solids has occurred on the tank walls. CAUTION (!aro nmst he (■x<'r<'is«M not to .■X >OM- tlio < vcs lo •Uro <•! iiltra\iolc 1 ra< lial ion. .4lHa\ •> turn he 1 amps olT vth< •11 th ■ 1; inks ai-e <• t-aiicd or \^ lien ihcv art' opciic* lor »'iil<'i iii^ <>r for iiis|M-cli<>ii. riti a\ioh-t 1 rays. <-an «!<> irr< parahlr (hiiiiag)' lo Ih.- evt's. The receiving tank (fig. 132) should be placed alongside a ramp so that the sap in the hauling tanks can be emptied into it by gravity. In some localities it is possible to have the receiving tanks installed higher than the storage tanks so that they also can be filled by gravity. Figure 132. — The sap is filtered as it receiving tank. PN-4828 is run into the 124 AGRICULTURE HANDBOOK 184, U.S. DEPT. OF AGRICULTURE However, the more common method is to move sap from the receiving: tanks to the storage tanks by i)iimi)s. Sap obtained from pijDelines is usually free of foreign matter and does not need to be filtered. However, sap obtained by other collecting methods must be filtered to remove fine parti- cles of bark and other foreign matter from the sap. If not removed, this foreign matter may serve as an unwanted source of color and cause the production of dark, low-gi-ade sirup.- The filter may be either a presscloth prefilter or several thicknesses of muslin (fig. 133). It is desirable to use two or more sap-storage tanks. This permits better control of sanitation, plant operation, and production records. The Brix value of the sap in each tank must be determined since it may be a composite of sap obtained from two or more sources that may be of different sugar contents. If the volume of sap in the tank and its Brix value are known, the yield of finished sirup can be calculated (see p. 48). The evaporator house must be provided with a gage to show the volume of sap in the storage tank being used to supply sap to the evapora- tor. Without a gage, the plant operator may unexpectedly find the supply of sap exhausted, and the evaporator pans may go diy and be damaged by bm-ning. A simple type of gage can be installed in the sap feed line from the tank to PN-1H29 Figure 133. — Several layers of muslin or presscloth can be used to filter sap. the evaporator This gage consists of a tee with a long, upright, glass sight tube, the top of which is open and above the level of the top of the storage tank. The level of the sap in the tube indicates its depth in the storage tank. The tube can be calibrated in units such as full, '/.,-full, etc., or in gallons. Handling und Storing Sirup Sirup tends to become darker each time it is heated above 18(F F. Therefore, sirup should be reheated as few times as possible. To insure a sterile package, all sirup must be packaged at temperatures above 19(F. It is advisable to package the sirup immediately after it leaves the filter or the finishing pan while it is still above 190^. If the temperature of the sirup drops below 19(]F before it can be packaged, a small amount of heat furnished by a steam coil with high-pressure steam, an electric immer- sion heater, or a heat lamp will bring it back to the desired 19(7 with a minimum of darkening. Sirup not immediately packaged can be put in bulk storage. If it is stored in drums, they must be completely filled with hot sirup (19(F F.). Large tanks holding several hundred or several thousand gallons can be used. Sirup storage tanks, like sap storage tanks, should be provided with germicidal lamps mounted to illuminate the entire surface of the sirup when the tank is filled. These lamps must be kept in operation continuously from the time the tanks are cleaned prior to filling until the last of the stored sirup has been removed. If the sirup is run into these tanks hot and sterile, there is little chance that any microbial gi'owth will occur below the sirup surface, and the germici- dal lamps will keep the surface sterile. Sirup stored in this way can be held indefinitely and sirup can be added or withdrawn at any time. It is not necessary to keep the tank cool. Tanks with sterile lamps can be mounted outside, for the ambient temperature has little or no effect on keeping quality of the sirup. The sirup with- drawn for packaging must be heated to sirup- pasteurizing temperature (190" F.). The large storage tank also serves as a set- tling tank. After several weeks of storage, the sirup will be sparkling clear. MAPLE SIRUP PRODUCERS MANUAL 125 SailitUtioil ^- Labor (supervisor plus hourly wages at $1.50 per hour) 1,255 The central evaporatinfj plant is a fond proc- essing: plant. It must be maintained in the same Total ' clean and sanitary manner that is required of . „ ^ . , , ..„,." F. Income (8,800 gallons of sirup produced; all food plants. price received per gallon, $4.3,'ir 38.104 The evaporator room and any other rooms m Net profit, F - (B + c+D + E), or $38,i04 - the plant should be kept free of steam. Moist $28,211 9,893 surfaces are sites for microbial growth. Steam Return on capital investment: is easily removed from the evaporators by us- ^ jqq ^ ^g percent " ing the closed venting system described on page $25,291 40. The floors should be constructed of smooth ' Except for average price per gallon of sirup, these . r 1 • data are adapted from Pasto and Taylor (86). masonry for ease of cleaning. , g^^ ^^^1^ jg j.^^ itemized capital expenditure. The sirup should be packaged in a separate :< p^^ed costs, with the possible exception of salaries room or area that can be kept clean and free of paid to management, remain constant irrespective of dust. Clean all equipment at frequent intervals. production. When detergents and scale-removing chemicals ] Cost of sap. This depends on two variables: (i) The , . , , i 1 J u volume of sap processed, and (2) the Brix (percent oi are used, they must be completely removed by ^^,g^^, ^^ ^^^ ^^p ^^^^ ^^^ ^^^^ ^^^^^^ p^^^ p^i^ f^,. ^^p at least three successive rinses with clean, clear ^f 2.4° Brix in 1963. water. ' The price received for a gallon of sirup is based on an Only clean utensils should be used and in- assumption that '/:, will be sold in bulk at $3 per gallon, 'A, Struments should be kept free of sugar sand. at a bulk price of $4, and V., sold retail at $6 per gallon. Return on capital for sirup at the plant; does not include marketing costs. Economics ^, , , , • ■ -1 r The previous data assume maximum produc- The central evaporator plant is primarily tor . ,. n i ^ t ^ t-- i^ ^ . , r. r, ■ I tion tor a small plant. Less production would concentrating sap to sirup and tor iiltering and , <.<■•* j • e ■ <- ^ r „ , ^ XI • -^ -11 u reduce net profit and income from invested packaging sirup. When used tor this, it will be . , operated only 6 to 8 weeks a year. Yet even with this short period of use, Pasto and Taylor (86) found in 1962 that such a plant could pay Material lialaun' an excellent return on the invested capital. The Seldom will the actual amount of sirup pro- following calculations, based on Pasto and Tay- duced equal that calculated from the amount of lor's data, show how profitable such an opera- gap purchased and the Brix value of the sap. tion could have been at that time. By recalcu- Pasto and Taylor (86) suggested that there is a lating, using current costs and prices, one could 2-percent loss in sirup. They suggested that this determine whether the return to be expected is due to sirup left sticking to the walls of the would be higher or lower than that shown here. evaporators, holding tanks, and felt filters. This apparent loss is caused (1) by making sirup that Returns on capitalinvestment in small central evaporator is too heavy (a Brix value above 66.(f), and plant used only for processing sap and filtering and selling this heavy sirup on a volume basis packaging sirup ' rather than on a weight basis; (2) by overfilling . , X i , . . . . cSc Of,, sirup containers; as little as 5-percent overfill in A. Investment in plant and equipment ■ $25,291 •, , , ■ , the retail package results in only 950 gallons oi Costs (operating): sirup for each LOGO gallons handled — a loss of B. Fixed (management, interest on borrowed 50 gallons; and (3) by removing during filtration capital, depreciation, repairs, insurance, sugar sand that was measured in sap as sugar. property taxes)' 6,277 ^p^^ longer the plant is in productive opera- Variable: " C. Sap supplies (322,292 gal. (2.4° Brix) at tion (hours and days) and the greater the vol- $0,052 per gal.)^ 16,7.59 ume of sirup produced, the greater will be the D. Fuel (26,136 gal. oil at $0.15) 3,920 profits and returns on the investment. 126 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE I iH-rcasinf! Returns Use of central plant facilities need not be limited to the 6 or 8 weeks of sap evafwration. Instead, the facilities can be put to a number of other uses that not only produce more income from the invested capital but also furnish prof- itable employment. Additional uses for the plant~are: (1) Mixing of sirups to obtain a standard grade and den- sity; (2) custom packaging of sirup; (3) prepar- ing gift packages; (4) reprocessing sirup to re- move buddy flavor; (5) making high-flavor sir- up; (6) preparing high-density sirup; and (7) manufacturing confections. Some additional equipment would be re- quired. This includes a steam kettle for use in processing sirup and in manufacturing confec- tions and a candy machine and facilities for manufacturing confections. Standardizing Sirup for Color and Density Today, the consumer exjjects uniformity in food products. The public, therefore, expects uniformity (year after year) in the color (gi-ade) and density of maple sirup. The color and den- sity can easily be adjusted to meet specific customer demands by mixing sirup of different grades and different densities. This must be done after the sirupmaking season so that the amount of different sirup stocks will be known. Adjiisliiif: Color To adjust the color, measure 1 cup of either the lighter sirup or the darker sirup in a 2-cup measurer. Then add the other with constant mixing until the desired color (grade) is reached. Note the amount of sirup added in ounces. This will give the ratio of the light and dark sirups to be mixed to produce the desired grade. Stirring sirup in .5-gallon tins makes it easier to select different gi-ades for mixing. Adjiisling Ih'iisilY To adjust the density, preferably to between 66^ and 67° Brix, the method of Pearson's Square can be used. Considerable time can be saved by calculating the number of parts (by weight) of the heavy sirup to mix with sap or thin sirup to obtain standard-density sirup. Example 1. If a dense sirup of 70^ Brix is to be mixed with a thin sirup of 64.4' Brix to make a standard-density sirup of 66.0^ Brix, the quan- tity of each sirup to be used can be determined by alligation as follows: A = 70 D = 1.6 (calculated) C = 66.0 B = 64.4 4.0 (calculated) where A = density of heavy sirup in ° Brix B = density of light sirup in ° Brix C = density desired as the result of mix- ing A and B This is always the center figure. D = the difference between C and B, which in this case = 1.6. E = the difference between A and C, which in this case = 4.0. D and E give the ratios of sirup A and B to mix to produce standard- density sirup (66.0P Brix), which in this case would be 1.6 parts of A (heavy sirup) to 4.0 parts of B (light sirup). Example 2. If sirup with a density of 66.5^ Brix is desired (it will feel better to the tongue) using the same two sirups, the Pearson Square would become 70 D = 2.1 C = 66.5 B = 64.4 E = 3.5 The ratio of these two sirups mixed to give a sirup having a density of 66.5" Brix (C) would be 2.1 parts of A (hea\y sirup) to 3.5 parts of B (light sirup). rii<;«'.s Many customers want sirup packaged in con- tainers of special design and shape. This re- quires special handling, and is usually done after the. sap season. MAPLE SIRUP PRODUCERS MANUAL 127 Many companies and some individuals are using gift packages for a selected clientele. These gift packages consist of a variety of maple products attractively packaged. Orders are usually received and made up for special occasions, particularly for the Christmas sea- son. Ili{>;h-Klavtions All well-managed central evaporator plants should have a candy kitchen for manufacturing confections (fig-s. 134-136). The cost of convert- ing standard-density sirup to confections is small compared to the selling price of the con- fections; confection manufacture is the most profitable enterprise of the central plant. The principal confections made are maple cream, PN-4k:!U Figure 13i. — A well-equipped candy kitchen with dehu- midifier and air-conditioner is an essential part of a central evaporator plant. The candy kitchen furnishes employment a major part of the year. PN-1831 Figure 135.— A central evaporator plant must have a salesroom for displaying- and selling the products manufactured. PN^832 Figure 136.— A large, easily read sign advertising the central evaporator plant is essential for directing the public to the plant for the purchase of maple products. maple candies (soft sugar), block sugar, and stirred sugar. The candy kitchen of the central plant will be in operation from 9 to 12 months of the year. The manufacture of confections may use more than half the plant's sirup production and will provide the largest source of income per gallon of sirup. A small central evaporator plant may produce more than 4 tons of confections a year. 128 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE .Siiniiiiar> (1) Theoi-etically, the central evai)orator plant is sound economically for both the plant investor and the suppliers of sap. (2) Locate it on an accessible, hard-surfaced, touri.st-traveled road. {'.i) The plant need not be larp:e, but the larger the plant, the larger the returns. Central evaporator plants are readily expanded. (4) The most common plant is one using oil fuel for the bulk of the sap evaporation and high-pressure steam for the last stage of the evaporation. (5) Utilize automation where jwssible. (6) Sap should be purchased on the basis of its Brix value and volume or weight. The price of sap should be on a sliding scale, vai-ying with the " Brix of the sap. (7) Standards of production should be set for sap producers. (8) Sap storage facilities must be adequate to handle a maximum day's run from all of the sap suppliers. (9) Sap tanks should be located in a cool place, easily accessible for washing and sanitiz- ing. Tanks should be provided with germi- cidal lamps to prevent sap deterioration by microbial s{X)ilage. (10) Bulk storage of sirup can be in large tanks protected by germicidal lamps or in 5-gal- lon tins or 30-gallon drums. (11) Sirup for retail trade should be mixed to obtain a standard color and density and packaged at 190P F. (12) Increased returns from the plant will re- sult from extending its use throughout the year by manufacturing confections, cus- tom-packaging sirup, and preparing gift packages of assorted maple products. REFERENCES CITED (1) Anonymous. 1975. SAP PRICES. Natl. Maple Syrup Digest 14 (1): 6. (la)ABDUL-WAHAB, N. S., HaBIB, A. T., and BROWN, H. D. 1957. THE INFLUENCE OF HEAT TREATMENT ON FLAVOR, COLOR AND SOME CHEMICAL CON- STITUENTS OF MAPLE SYRUP. Amer. Soc. Hort. Sci. Proc. 69: 480-484. (2) Arnold, E. L. 1960. using water pumps for gathering ma- PLE SAP. Vt. Agr. Expt. Sta. Bui. 616, 2.3 pp. (3) BaGGLEY, G. F., and MaCHWART, G. M. 1947. MAPLE SYRUP MANUFACTURE, USING A VACUUM EVAPORATOR. Interdepartmental Communication of Michigan College of Min- ing and Technology, 28 pp. [Processed.] (4) Balch, R. T. 1930. MAPLE SIRUP COLOR STANDARDS. Indus, and Engin. Chem. 22: 255-257, illus. (5) Bell, R. D. 1955. costs and returns in producing and marketing maple products in new york STATE. Cornell Univ., Dept. Agr. Econ., A. E. 1016, 43 pp., illus. (Processed.! (6) Betts, H. S. 1945. MAPLE (ACER SPECIES). U.S. Forest Serv., Amer. Woods ISer.l, 12 pp., illus. (7) Blum, B. M., and KOELUNG, M. R. 1968. VACUUM PUMPING INCREASES SAP YIELDS FROM SUGAR MAPLE TREES. U.S. Forest Serv., Northeast. Forest Expt. Sta., Res. Pa- per NE-106. 14 pp. (8) Bond. A. D. 1948. COSTS AND RETURNS IN PRODUCING MAPLE SYRUP; 20 FARMS, NEW YORK, 1947. N.Y. Univ. Dept. Agr. Econ. and Farm Mangt., A. E. 661, 13 pp., illus. [Processed.] (9) BRICE, B. a., and TURNER, A., jR. 1956. GLASS COLOR STANDARDS FOR MAPLE SIR- UP. Jour. Optic. Soc. Amer. 46: 293-299. (10) Turner, a., Jr., Southerland, F. L., and BOSTWICK, E. p. 1950. permanent glass COLOR STANDARDS FOR maple sirup. U.S. Bur. Agr. and Indus. Chem. AIC-260, ]4] pp., illus. [Processed.] (11) Burns, M., and Personious, C. J. 1962. using maple sirup. N.Y. (Cornell) Agr. Ext. Serv. Bui. 985, 8 pp. (12) Canada Department of Agriculture. 1961. maple syrup, sugar, butter, taffy. Canada Dept. Agr. Pub. 1096, 23 pp. (1.3) Ching, T. M., and Mericle, L. W. 1960. SOME EVIDENCE OF PREMATURE STOPPAGE OF SUGAR MAPLE PRODUCTION. Forest Sci. 6: 270-275. (14) COLUNGWOOD, G. H., COPE, J. A., and RaSMUSSEN, M. P. 1935. THE PRODUCTION OF MAPLE SIRUP AND SUGAR IN NEW YORK STATE. N.Y. Agr. Col. (Cornell) Ext. Bui. 167, 78 pp., illus. (Rev.) (1.5) Connelly, J. A. 1969. TWO AUTOMATIC SIRUP DRAWOFF CON- TROLLERS. U.S. Agr. Res. Serv. ARS 73-60, 12 pp. MAPLE SIRUP PRODUCERS MANUAL 129 (22) (23) (27) (28) (29) Cool, B. M. 1957. an investigation of the effect of some production techniques and weather factors on maple sap and sugar fields IN A CENTRAL MICHIGAN WOODLOT. (Thesis for degree of Ph. D., Mich. State Univ. Micro- filmed.] COSTILOW, R. N., ROBBINS, P. W., SIMMONS, R. J., and WiLUTS, C. O. 1962. THE EFFICIENCY AND PRACTICABIUTY OF DIFFERENT TYPES OF PARAFORMALDEHY'DE PELLETS FOR CONTROLLING MICROBIAL GROWTH IN MAPLE TREE TAPHOLES. Mich. Agr. Expt. Sta. Quart. Bui. 44: 5.59-.579. Davis, D. R., Hacskaylo, J., Gallander, J., and QinNN, F. 1962. SUGAR SANDS ARE IMPORTANT PART OF MA- PLE SUGAR RESEARCH. Ohio Farm and Home Res. 47 (2): 24-25, 30, illus. Desilets, D. 1972. the application of vacuum for maple SAP COLLECTION. (Unpublished. Copy on file, Northeast. Forest Expt. Sta., Burling- ton, Vt.] Dunn, S., and Townsend, R. J. 1954. PROPAGATION OF SUGAR MAPLE BY VEGE- TATIVE CUTTINGS. Jour. Foresti-y 52: 678- . 679. DYCE, E. J. 1935. HONEY PROCESS AND PRODUCT. (U.S. Pat- ent No. 1,987,893.) U.S. Patent Office, Off. Gaz. 4.50: 613. ElCHMEIER, A. H. 1955. WEATHER AND MAPLE SYRUP. U.S. Weather Bur., Weekly Weather and Crop Bui. 42(3): 7-8, illus. jpi-ocessed.] Energy Control Co. of New York, N.Y. 1952. new thermometer simpufies maple sir- UP PRODUCTION. Energy 14 (3): [5], illus. England, G. M., and Enoch, H. T. 1956. MARKETING VERMONT'S MAPLE SYRUP. Vt. Agr. Expt. Sta. Bui. .593, 27 pp., illus. FiLiPic, V. J., Underwood, J. C, and Dooley, C. J. 1969. TRACE COMPONENTS OF THE FLAVOR FRAC- TION OF MAPLE SYRUP. Jour. Food Sci. 34: 10.5-110. FOULDS, R. (n. d.l TAP YOUR TREES. Vt. Agr. Ext. Ser., 5 pp. (Unnumb. pub.) Frank, H. A. 1962. INFLUENCE OF LOW INCUBATION TEMPERA- TURE ON CLASSIFICATION OF PSEUDOMONAS GENICULATA. Jour. Bact. 84: 68-71. NaGHSH, J., Reed, L. L., and WiLLITS, C. 0. 1959. MAPLE SIRUP. XII. THE EFFECT OF ZINC ON THE GROWTH OF MICRO-ORGANISMS IN MA- PLE SAP. Appl. Microbiol. 7: 152-155. and WiLUTS, C. O. 1960. MAPLE SIRUP. XIII. STERIUZING EFFECT OF SUNLIGHT ON MAPLE SAP IN TRANSPARENT TUBES. Appl. Microbiol. 8: 141-145. (:30) and WiLLITS, C. 0. 1961. MAPLE SIRUP. XVII. PREVENTION OF MOLD AND YEAST GROWTH IN MAPLE SIRUP BY CHEMICAL INHIBITORS. Food Technol. 15: 1- 3. (31) and WiLLITS, C. O. 1961. MAPLE SIRUP. XVIII. BACTERIAL GROWTH IN MAPLE SAP COLLECTED WITH PLASTIC TUBING. Food Technol. 15: 374-378. (32) Gabriel, W.J. 1963. SWEET SUGAR MAPLES WANTED. Natl. Ma- ple Syrup Digest 2 (2): 10. (33) Marvin, J. W., and Tay'lor, F. H. 1961. ROOTING GREENWOOD CUTTINGS OF SUGAR MAPLE— EFFECT OF CLONE AND MEDIUM. U.S. Forest Serv., Northeast. Forest Expt. Sta., Sta. Paper 144, 14 pp. (34) Greene, M. T., and Marvin, J. W. 1958. THE WATER CONTENT OF MAPLE STEMS. I. APPLICATION OF THE KARL FISCHER METHOD FOR THE ANALYSES OF WATER IN MAPLE BARK AND WOOD. Plant Physiol. 3.3: 169- 173. (35) and Marvin, J. W. 1958. THE WATER CONTENT OF MAPLE STEMS. II. APPARENT CHANGES IN THE WATER CON- TENT OF MAPLE STEMS AND THE PHYSIOI^ OGY OF MAPLE SAP FLOW. Plant Physiol. 33: 173-176. (.36) Henshaw, H. W. 1890. INDIAN ORIGIN OF MAPLE SUGAR. Amer. An- throp. .3: 341-.351, illus. (36a) Hills, C. H., and BELL, R. A., jR. 1975. REMOVAL OF BUDDY FLAVOR FROM MAPLE SIRUP. Natl. Maple Syrup Digest 14 (1): 12- 13. (37) Hubbell, C. In.d.l THE ART OF MAKING MAPLE CREAM. 6 pp. Jefferson, N.Y. [Mimeographed.] (38) Jones, a. r. c. 1962. plastic tubing or sap buckets. mac- Donald Farm, pp. 1-3. (Mar.) (.39) Jones, C. H., Edson, a. W., and MORSE, W. J. 1903. THE MAPLE SAP FLOW. Vt. Agr. Expt. Sta., Bui. 103, pp. [411-84, illus. (40) Jones, G. a. 1961. WE CAN INCREASE SAP \TELDS. MacDonald Farm, pp. 1-3. (Feb.) (41) 1962. CHEMICALS TO INCREASE SAP Y'lELDS. MacDonald Farm, pp. 1-2. (Jan.) (42) Jordan, W. K., Kosikowsh, K. V., and March, R. P 1954. FULL-FLAVORED MAPLE SYRUP PROCESS PUTS IDLE DAIRY UNITS TO WORK. Food En- gin. 26 (5): 70-71. 179, illus. (43) KISSINGER, J. C, and BELL, R. A. 1972. AN ECONOMICAL ULTRAVIOLET-IRRADIATION UNIT FOR PASTEURIZING FLO'AHNG MAPLE SAP. U.S. Agr. Res. Serv. ARS 7.3-71, 11 pp. 130 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE (44) KOELUNG, M. R. 1972. VACUUM PRODUCING EQUIPMENT FOR MAPLE SAP OPERATIONS. U.S. Agr. Res. Serv. ARS 73-73, 12-16. (45) KRIEBEL, H. B. 1957. PATTERNS OF GENETIC VARIATION IN SUGAR MAPLE. Ohio Agr. Expt. Sta. Res. Bui. 791, 56 pp., illus. (46) 1961. FERTIUZATION INCREASES SAP SWEETNESS IN SUGAR BUSH. Ohio Farm and Home Res. 46 (6): 92-93, illus. (47) LainG, F. M., and ARNOLD, E. L. 1971. USE OF VACUUM IN PRODUCTION OF MAPLE SAP: PROGRESS REPORT. Vt. Agr. Expt. Sta. Res. Rpt. MP-64, 17 pp. (48) LIGHTHALL, M. T. G., and MARVIN, J. W. 1960. THE USE OF PLASTIC TUBING IN GATHERING MAPLE SAP. Vt. Agr. Expt. Sta. Pam. 32, 11 pp., illus. (49) LIGHTHALL, M. T. G., and Marvin, J. W. 1962. STUDIES ON PIPEUNE SYSTEMS FOR GATH- ERING MAPLE SAP. Prog. Rpt. No. 1. Vt. Agr. Expt. Sta. Misc. Pub. 17, 5 pp. (50) Marvin, J. W., and Lighthall, M. T. G. 1962. EFFECT OF NEW TECHNIQUES ON MAPLE SAP YIELDS. Prog. Rpt. No. 2. Vt. Agr. Expt. Sta. Misc. Pub. 20, 10 pp. (51) Lamb, A. F., and PersonIUS, C. J. 1957. USING MAPLE SIRUP. N.Y. (Cornell) Agr. Ext. Serv. Bui. 985, 8 pp. (52) Lento, H. G., Jr., Underwood, J. C, and willits, CO. 1958. BROWNING OF SUGAR SOLUTIONS, n. EF- FECT OF THE POSITION OF AMINO GROUP IN THE ACID MOLECULE IN DILUTE GLUCOSE SOLUTIONS. Food Res. 23: 68-71. (53) UNDERWOOD, J. C, and WILUTS, C. O. 1960. BROWNING OF SUGAR SOLUTIONS. IV. THE EFFECT OF PH ON THE VOLATILE PRODUCTS OF REDUCING SUGARS. Food Res. 25: 750- 756. (54) Underwood, J. C., and Willits, c. O. I960. BROWNING OF SUGAR SOLUTIONS. V. EF- FECT OF PH ON THE BROWNING OF TRIOSES. Food Res. 25: 757-763. (55) Little, E. L., Jr. 1953. check ust of native and naturalized trees of the united states (including ALASKA). U.S. Dept. Agr., Agr. Handb. 41, 472 pp. (56) Maroney, R. H. 1950. TRENDS IN EVAPORATOR DESIGN. Conf. on Maple Prod. (U.S. Bur. Agr. and Indus. Chem., East. Reg. Res. Lab., Philadelphia, Nov. 13-15), Rpt. Proc. Ill: 29-30. [Processed.] (57) Marvin, J. W. 1949. CHANGES IN BARK THICKNESS DURING SAP FLOW IN SUGAR MAPLES. Science 109: 231- 232, illus. (58) and GREENE, M. T. 1951. TEMPERATURE-INDUCED SAP FLOW IN EX- CISED STEMS OF ACER. Plant Physiol. 26: 565-580, illus. (59) and GREENE, M. T. 1959. SOME FACTORS AFFECTING THE YIELD FROM MAPLE TAPHOLES. Vt. Agr. Expt. Sta. Bui. 611, 28 pp., illus. (60) Meeker, e. W. 1950. CONFECTIONERY SWEETENERS. Food Tech- nol. 4: 361-365, illus. (61) M^HOT, J. R., and ROMPRfe, N. 1953. MAPLE SUGAR INDUSTRY IN QUEBEC. Que- bec Dept. Agr. Bui. 169, 48 pp., illus. (62) MONEY, R. W., and BoRN, R. 1951. EQUILIBRIUM HUMIDITY OF SUGAR SOLU- TIONS. Jour. Sci. Food and Agr. 2: 180-185, illus. (63) MooRE, H. R., ANDERSON. W. R., and Baker, R. H. 1951. OHIO MAPLE SYRUP . . . SOME FACTORS IN- FLUENCING PRODUCTION. Ohio Agr. Expt. Sta. Res. Bui. 718, 53 pp., illus. (64) MORROW, R. R. 1952. CULLING SUGAR BUSH FOR LOW-COST PRO- DUCTION. Farm Res. I N.Y. State Agr. Expt. Sta.l 18(1): 7, illus. (65) 1953. (66) (67) (68) (69) (70) (71) (72) (73) BIG TREE CROWNS MEAN CHEAPER SIRUP. Farm Res. [N.Y. State Agr. Expt. Sta.] 19(1): 12. EARLY TAPPING FOR MORE QUALITY SIRUP. Jour. Forestry 53: 24-25. INFLUENCE OF TREE CROWNS ON MAPLE SAP PRODUCTION. N.Y. (Cornell) Agr. Expt. Sta. Bui. 916, 30 pp., illus. PLASTIC TUBING TESTED FOR MAPLE SAP PRODUCTION. Farm Res. [N.Y. State Agr. Expt. Sta.] 24: (3), 4-5, illus. HARDWOOD FUEL FOR BOILING MAPLE SAP? Farm Res. [N.Y. State Agr. Expt. Sta.J 25: (4), 2, illus. PLASTIC TUBING FOR MAPLE SAP. Farm Res. (N.Y. State Agr. Expt. Sta.] 27: (2), 12- 13. RELATIVE VALUES IN MAPLE SIRUP ENTER- PRISES. Dept. Mimeo. C-32. INFLUENCE OF NUMBER AND DEPTH OF TAP HOLES ON MAPLE SAP FLOW. N.Y. (Cornell) Agr. Expt. Sta. Bui. 982, 12 pp. THE APPUCATION OF VACUUM IN SUGAR BUSHES. N.Y. State Col. Agr. (Cornell), Dept. Conserv., Res. Ser. No. 1, 19 pp. MAPLE SIRUP PRODUCERS MANUAL 131 (74) NAGHSK], J. 1953. THE ORGANISMS OF MAPLE SAP: THEIR EF- FECT AND CONTROL. (Summary) Second Conf. on Maple Prod. (U.S. Agr. Res. Serv., East. Util. Res. Br., Philadelphia, Nov. 16- 18). Rpt. Proc. 2: 48-52. [Processed.] (75) REED, L. L., and WILLITS, C. O. 1957. MAPLE SIRUP. X. EFFECT OF CONTROLLED FERMENTATION OF MAPLE SAP ON THE COLOR AND FLAVOR OF MAPLE SIRUP. Food Res. 22: 176-181. (76) and WILLITS, C. O. 1953. MAPLE SIRUP. VI. THE STERILIZING EFFECT OF SUNLIGHT ON MAPLE SAP COLLECTED IN A TRANSPARENT PLASTIC BAG. Food Technol. 7: 81-83, illus. (77) and WILLITS, C. O. 1955. MAPLE SIRUP. IX. MICROORGANISMS AS A CAUSE OF PREMATURE STOPPAGE OF SAP FLOW FROM MAPLE TAP HOLES. Appl. Mi- crobiol. 3: 149-151, illus. (78) and WILLITS, C. O. 1956. TESTING MAPLE SIRUP FOR CREAMING. U.S. Dept. Agr. Leaflet 400, 8 pp., illus. and WILLITS, C. O. 1957. MAPLE SIRUP. XI. RELATIONSHIP BETWEEN THE TITE AND ORIGIN OF REDUCING SUGARS IN SAP AND THE COLOR AND FLAVOR OF MA- PLE SIRUP. Food Res. 22: 567-571. WILUTS, C. O., and PORTER, W. L. 1955. MAPLE SIRUP. VIII. A SIMPLE AND RAPID TEST FOR THE ANALYSIS OF MAPLE SIRUP FOR INVERT SUGAR. Food Res. 20: 138-143. WILLITS, C. O., Porter, W. L., and White. J. W., Jr. 1956. MAPLE-HONEY SPREAD AND PROCESS OF MAKING THE SAME. U.S. Patent No. 2,760,870. New Hampshire Maple Producers Associa- tion Inc. 1962. new HAMPSHIRE MAPLE SYRUP— ITS CARE AND USE. 15 pp. Concord. (Rev.) New York State Department of Agriculture AND Markets. 1956. new YORK state official standards, definitions, rules and regulations for MAPLE products. EFFECTIVE APRIL 1.1, 1941. N.Y. State Bur. Mkts. .300—5/16/56, pp. [Processed.] Paine, H. S. 1924. constructive chemistry in relation to CONFECTIONERY MANUFACTURE. Indus, and Engin. Chem. 16: 51.3-517. 1929. CANDY MAKERS CONTROL SOFTENING ( CREAM CENTERS. Food Indus. 1: 200-202, illus. Pasto, J. K., and Ta-^-LOR, R. D. 1962. ECONOMICS OF THE CENTRAL EVAPORATOR IN MAPLE SYRUP PRODUCTION. Pa. Agr. Expt. Sta. Bui. 697, 28 pp. (79) (80) (81) (82) (83) (84) (85) (87) Phillips, G. W. M., and Homiller, R. P. 1953. oil firing FOR THE MAPLE SIRUP EVAPO- RATOR. U.S. Bur. Agr. and Indus. Chem. AIC>-3.58, [10] pp., illus. [Processed.] (88) Pollard, J. K., Jr., and Sproston, T. 1954. nitrogenous constituents of sap EX- UDED FROM THE SAPWOOD OF ACER SAC- CHARUM. Plant Physiol. 29: .360-364, illus. (89) Porter, w. L., Buch, m. L., and WILLITS, c. O. 1951. MAPLE SIRUP, ni. preliminary STUDY OF the nonvolatile acid fraction. Food Res. 16: .338-341. (90) Buch, M. L., and WiLUTS, C. O. 1952. MAPLE SIRUP. IV. effect OF HEATING SIRUPS under CONDITIONS OF HIGH TEM- PERATURE and LOW WATER CONTENT: SOME PHYSICAL AND CHEMICAL CHANGES. Food Res. 17: 475^81, illus. (91) HOBAN, N., and WILLITS, C. O. 1954. CONTRIBUTION TO THE CARBOHYDRATE CHEMISTRY OF MAPLE SAP AND SIRUP. Food Res. 19: 597-602, illus. (92) ROBBINS, P. W. 1947. THE COST OF MAKING MAPLE SIRUP. Mich. Agr. E.xpt. Sta. Quart. Bui. 29: 188-189. (93) (94) 1948. POSITION OF TAPPING AND OTHER FACTORS AFFECTING THE FLOW OF MAPLE SAP. [Unpublished Master's Thesis. 0>py on file in library, Mich. State Univ., East Lansing.) 1953. FACTORS INFLUENCING THE PRODUCTION OF HIGH QUAUTY MAPLE SAP. (Summary) Sec- ond Conf. on Maple Prod. (U.S. Agr. Res. Serv., East. Util. Res. Br., Philadelphia, Nov. 16-18). Rpt. Proc. 2: 34-36. [Processed.] 1960. THE YIELD OF MAPLE SAP PER TAPHOLE. Mich. Agr. Expt. Sta. Quart. Bui. 43: 142- 146. [n. d.] INFLUENCE OF TAPPING TECHNIQUES ON MAPLE SAP YIELDS. Mich. Agr. Expt. Sta. Farm Sci. Res. Rpt. 28, 3 pp. (97) SanfoRD, M. 1962. BorUNG SAP WITH STEAM. 4 pp. Little Uen- esee, N.Y. [Unnum. Mimeo.] (98) Sattler, L., and Zerban, F. W. 1949. unfermentable reducing substances in MOLASSES. Indus, and Engin. Chem. 41: 1401-1406, illus. (99) SCARBOROUGH, N. F. 1932. THE CRYSTALUSATION OF CONFECTIONERY. Food Technol. [London] 2: 1—1. illus. (100) SCHNEIDER, I. S., Frank, H. A., and WILLITS, C. 0. 1960. MAPLE SIRUP. XIV. ULTRAVIOLET IRRA- DIATION EFFECTS ON THE GROWTH OF SOME BACTERIA AND YEASTS. Food Res. 25: 654- 662. 132 AGRICULTURE HANDBOOK VU, U.S. DEPT. OF AGRICULTURE (101) SCHUETTE, H. A., and SCHUETTE, S. C. 1935. MAPLE SUGAR: A BIBLIOGRAPHY OF EARLY RECORDS. Wis. Acad. Sci., Art.s Letters Trans. 29: 209-236. (102) SHENEMAN, J. M., and COSTlU)W, R. N. 1959. IDENTIFICATION OF MICROORGANISMS FROM MAPLE TREE TAPHOLES. Food Res. 24; 146- 151. (103) COSTILOW, R. N., ROBBINS, p. W., and DOUG- LASS, J. E. 1959. CORRELATION BETWEEN MICROBIAL POPU- LATIONS AND SAP YIELDS FROM MAPLE TREES. Food Res. 24: 152-159. (104) SIPPLE, L., WILUTS, C. O.. and WINCH, F. E., JR. 1963. ARCHES AND BURNERS FOR OIL-FIRED MA- PLE SAP EVAPORATORS. U.S. Agr. Res. Serv. ARS 73^0, 14 pp., illus. (105) Smith, H. C. 1971. sap volume flow as influenced by tub- ing diameter and slope percent. u.s. Forest Serv., Northeast. Forest Expt. Sta. Res. Note NE-137, 6 pp. (106) and GIBBS, C. B. 1970. COMPARISON OF VACUUM AND GRAVITY SAP FLOWS FROM PAIRED SUGAR MAPLE TREES. U.S. Forest Serv., Northeast. Forest Expt. Sta. Res. Note NE-122, 4 pp. (107) Snyder, C. F.. and Hammond, L. D. 1946. WEIGHTS PER UNITED STATES GALLON AND WEIGHTS PER CUBIC FOOT OF SUGAR SOLU- TIONS. I U.S.I Natl. Bur. Standards Cir. 457, 28 pp. [Processed.! (108) Sproston, T., Jr., and LANE, S. 1953. MAPLE SAP contamination AND MAPLE SAP BUCKETS. Vt. A}jr. Expt. Sta. Pam. 28, 4 pp. (109) and SCOTT, W. W. 1954. VALSA LEUCOSTOMOIDES, THE CAUSE OF DECAY AND DISCOLORATION IN TAPPED SUGAR MAPLES. Phytopathology 44: 12-13, illus. (110) STEVENSON, D. D., and BaRTOO. R. A. 1940. COMPARISON OF THE SUGAR PER CENT OF SAP IN MAPLE TREES GROWING IN OPEN AND DENSE GROVES. Pa. State Forest Sch. Res. Paper 1, 3 pp. [Processed.! (111) Strolle, E.g., Cording, J., Jr., and Eskew, R. K. 1956. AN ANALYSIS OF THE OPEN-E'AN MAPLE- SIRUP EVAPORATOR. U.S. Agr. Res. Serv. ARS 73-14, 14 pp., illus. (112) TAYLOR, F. H. 1956. VARIATION IN SUGAR CONTENT OF MAPLE SAP. Vt. Agr. Expt. Sta. Bui. 587, 39 pp. (113) Trenk, F. B., and McNall, P. E. 1954. COSTS OF PRODUCING MAPLE SYRUP IN Wl.s- CONSIN. IWis. Agr. Expt. Sta.! 6 pp., il- lus. [ Processed. 1 (114) TRESSLER, C. J., and ZIMMERMAN, W. 1. 1942. THREE YEARS' OPERATION OF AN EXPERI- MENTAL SUGAR BUSH. N.Y. State (Geneva) Agr. Expt. Sta. Bui. 699, 24 i)p.. illus. (115) (116) (117) Underwood, J. C. 1963. QUICK TEST FOR "BUDDY" FLAVOR IN MAPLE SIRUP. U.S. Agr. Res. Serv. ARS 7.3-12, 4 pp. EFFECT OF HEAT ON THE FLAVORING COM- PONENTS OF MAPLE SIRUP: A PRELIMINARY STUDY BY GAS CHROMATOGRAPHY. Jour. Food Sci. 36: 228-230. and FlUPIC, V. J. GAS CHROMATOGRAPHIC IDENTIFICATION OF COMF'ONENTS IN MAPLE SIRUP FLAVOR EX- TRACT. Assoc. Off. Agr. Chem. Jour. 46: 334-337. (118) (119) (120) (121) (122) (123) (124) (125) (126) (127) and LENTO, H. G. 1960. SOME PHYSICAL CHARACTERISTICS OF THE 2,4-DINITROPHENYLHYDRAZINE AND SEMI- CARBAZIDE DERIVATIVES OF THREE-CARBON CARBONYLS. Anal. Chem. 32: 1656-1658. LENTO, H. G., Jr., and WiLLITS, C. O. 1956. TRIOSE COMPOUNDS IN MAPLE SIRUP. Food Res. 21: 589-597. Lento, H. G., Jr., and Willits, C. O. 1959. BROWNING OF SUGAR SOLUTIONS. 3. EF- FECT OF PH ON THE COLOR PRODUCED IN DILUTE GLUCOSE SOLUTIONS CONTAINING AMINO ACIDS WITH THE AMINO GROUP IN DIFFERENT POSITIONS IN THE MOLECULE. Food Res. 24: 181-184. and WILUTS, C. O. 1959. SCALE IN MAPLE-SIRUP EVAPORATORS- HOW TO REMOVE IT. U.S. Dept. Agr. Inform. Bui. 203, 4 pp. Willits, C. O., and Lento, H. G. 1961. BROWNING OF SUGAR SOLUTIONS. VI. ISO- LATION AND CHARACTERIZATION OF THE BROWN PIGMENT IN MAPLE SIRUP. Jour. Food Sci. 26: 397-400. WILUTS, C. O., and LENTO, H. G. 1961. MAPLE SIRUP. XVI. ISOLATION AND IDEN- TIFICATION OF COMPOUNDS CONTRIBUTING TO THE FLAVOR OF MAPLE SIRUP. Jour. Food Sci. 26: 288-290. United States Department of Agriculture. 1949. trees; the yearbook of agriculture, 1949. 944 pp., illus. Washington, (Various references to maple sugar.) 1952. AGRICULTURAL STATISTICS 19!-.2. 876 pp. Washington. 1956. AGRICULTURAL STATISTICS ig.'io. 610 pp. Washington. 1963. AGRICULTURAL STATISTICS 19fi2. 741 pp. Washington. (128) 1972. AGRICULTURAL STATISTICS 197 Washington. 759 pp. MAPLE SIRUP PRODUCERS MANUAL 133 (129) United States Department of Agriculture, Consumer and Marketing Service. 1967. united states standards for grades of TABLE MAPLE SIRUP. (Effective May 24, 1967). 2 pp. (Processed.! (130) UNITED States Food and Drug Administra- tion. 1962. FOOD additives. Fed. Register 27: 1554. (130a) 1974. FOOD LABEUNG. Fed. Register 39: 20882. (131) Vermont Department of Agriculture. 1950. vermont maple syrup grading and marketing law, effective march 1, ig.'iO. Vt. Dept. Agr., Div. Mkts. Cir. 14, 16 pp. (132) Vermont Development Department and Ver- mont Department of Agriculture. 1962. VERMONT maple sirup and SUGAR. 16 pp., illus. Montpelier, Vt. (Rev.) (133) Wasserman, a. E. 1963. microbiology and sanitation in the sugar bush and sugar house. u.s. agr. Res. Serv. ARS 73-41, 18 pp., illus. (134) 1964. (135) 1962. (136) 1961. (137) MAPLE SIRUP. XXII. CONTROLLED FER- MENTATION OF BUDDY MAPLE SIRUP. Food Techno!. 18: 142-145. UNDERWOOD, J. C, and WiLUTS, C. O. FLUFFED MAPLE PRODUCTS — A NEW USE FOR MAPLE SIRUP. U.S. Agr. Res. Serv. ARS 73-39, 6 pp. and WILLITS, C. O. MAPLE SIRUP. XX. CONVERSION OF "BUDDY" MAPLE SAP INTO NORMAL MAPLE SIRUP. Food Technol. 15: 438-439. - and WILLITS, C. O. In. d.l PREPARATION OF MAPLE SIRUP FROM BUDDY SAP. Filed in Patent Office 10/17/61 as Serial No. 145,783. (Pat. pending.) (138) WEBER, P. D. 1956. WISCONSIN MAPLE PRODUCTS; PRODUCTION AND MARKETING. Wis. Dept. Agr. Bui. 335, 48 pp., illus. (139) Whitby, G. S. 1936. manufacture of maple products of in- TENSE FLAVOR. (U.S. Patent No. 2,054,873.) U.S. Patent Office, Off. Gaz. 470: 787. (140) WiLUTS, C. 0. 1951. CROPS FROM THE MAPLE TREES. U.S. Dept. Agr. Ybk. Separate 2208. [Reprint from Yearbook of Agriculture, 1950-1951: 316- 321.) (141) (142) 1953. SOME CHANGES THAT SAP UNDERGOES IN A CONTINUOUS ATMOSPHERIC EVAPORATOR. Second Conf. on Maple Prod. (U.S. Agr. Res. Serv., East. Util. Re.s. Br., Philadelphia, Nov. 16-18). Rpt. Proc. 2: 30-32. [Processed.] MAPLE AIDS IN BETTER LAND USE PRO- GRAM. Natl. Maple Syrup Digest 1 (3): 8, 10. (143) 1962. MODERNIZATION OF THE MAPLE SYRUP IN- DUSTRY. Natl. Maple Syrup Digest 1 (1): 6- 7. (144) Frank, H. A., and Bell, R. A. 1959. CLEANING PLASTIC EQUIPMENT USED IN HANDLING MAPLE SAP. U.S. Agr. Res. Serv. ARS 73-23, 12 pp. (145) Frank, H. a., and Underwood, J. C. 1960. MAKING HIGH-DENSITY, HIGH-FLAVORED MAPLE SIRUP. U.S. Agr. Res. Serv. ARS 73- 26, 8 pp. (146) Frank, H. A., and Underwood, J. C. 1960. MEASURING THE SUGAR IN MAPLE SAP AND SIRUP. U.S. Agr. Res. Serv. ARS 73-28, 21 pp. (147) Frank, H. A., and Underwood, J. C. 1961. filtration of maple SIRUP. Jour. For- esti-y 59: 112-113. (148) and PORTER, W. L. 1950. MAPLE SIRUP. II. A NEW HIGH-FLAVORED MAPLE SIRUP. U.S. Bur, Agr. and Indus. Cheni. AIC-269, 3 pp. (149) and PORTER, W. L. 1955. PRODUCTION OF MAPLE SUGAR PRODUCTS HAVING ENHANCED FLAVOR. (U.S. Patent No. 2,715,581.) (150) Porter, W. L., and Buch, M. L. 1952. MAPLE SIRUP. V. FORMATION OF COLOR DURING EVAPORATION OF MAPLE SAP TO SIRUP. Food Res. 17: 482-186, illus. (151) SHOLETTE, W. p., and UNDERWOOD, J. C. 1958. THE DETERMINATION OF MALIC ACID IN MA- PLE SIRUP BY AN ION EXCHANGE PROCE- DURE: AN ADAPTATION OF THE GOODBAN AND STARK METHOD. Assoc. Off. Agr. Chem. Jour. 41: 658-662. '152) and SiPPLE, L. 1961. THE USE OF PLASTIC TUBING FOR COLLECT- ING AND TRANSPORTING MAPLE SAP. U.S. Agr. Res. Serv. ARS 73-35, 19 pp., illus. (153) and UNDERWOOD, J. C. 1961. METHODS OF ANALYSIS FOR MAPLE SIRUP: USDA COLOR COMPARATOR. Assoc. Off Agr. Chem. Jour. 44: 330-333. (154) Underwood, J. C, and Lento, H. G. 1959. PROCESS FOR MAKING MAPLE PRODUCT OF INTENSIFIED MAPLE FLAVOR. (U.S. Patent No. 2,895,833.) (155) Underwood, J. C, Lento, H. G., Jr., and RICCIUTI, C. 1958. browning of SUGAR SOLUTIONS. I. EF- FECT OF PH AND TYPE OF AMINO ACID IN DILUTE SUGAR SOLUTIONS. Food Res. 23: 61-67. (1.56) Winch, F. E., Jr. in. d.l bacterial control for higher quality SAP. Inform. Sheet. (157) and MORROW, R. R. 1962. PRODUCTION OF MAPLE SIRUP AND OTHER MAPLE PRODUCTS. N.Y. (Cornell) Agr. Ext. Bui. 974, 40 pp. (Rev.) 134 AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE SUPPLEMENTAL READING Anonymous. 1940. maple sugar [sirup] in cigarettes. can- ada Lumberman 60 (8): 12. 1942. CANADIAN MAPLE HARVEST. Jour. Forestry 40: 806. _ ANDERSON, W. R., and METEER, J. W. 1948. MAKING FARM FORESTRY PAY. Ohio Forestry Assoc. News Bui. 1 (2): 111-2. ASHE, W. W. 1897. THE POSSIBIUTIES OF A MAPLE SUGAR INDUS- TRY IN WESTERN NORTH CAROLINA. N.C. Geol. Survey, Econ. Papers 1, 34 pp., illus. BARRACLOUGH, K. E. 1952. MAPLE SYRUP AND SUGAR PRODUCTION IN NEW HAMPSHIRE. N.H. Univ. [Agr.) Ext. Bui. 103. 28 pp., illus. BATES, F. J., and BeARCE, H. W. 1918. NEW BAUM6 SCALE FOR SUGAR SOLUTIONS. [U.S.] Natl. Bur. Standards Technol. Papers 115, 11 pp. BERKSHIRE Pioneer Maple Producers' Association. In. d.l MASSACHUSETTS PURE MAPLE SYRUP. 7 pp. Ashfield, Mass. Bryan, A. H. 1910. MAPLE-SAP SIRUP: ITS MANUFACTURE, COM- POSITION, AND EFFECT OF ENVIRONMENT THEREON. U.S. Bur. Chem. Bui. 134, 110 pp, illus. Hubbard, W. F., and Sherwood, s. F. [1923.1 PRODUCTION OF MAPLE SIRUP AND SUGAR. U.S. Dept. Agr. Farmers' Bui. 1366, 35 pp., illus. (Rev. 1937.) StraUGN, M. N., Church, C. G., and others. 1917. MAPLE SUGAR: COMPOSITION, METHODS OF ANALYSIS, EFFECT OF ENVIRONMENT. U.S. Dept. Agr. Bui. 466, 46 pp., illus. CHITTENDEN, A. K., and ROBBINS, P. W. 1930. THE COST OF MAKING MAPLE SYRUP. In The Farm Woodlot in Michigan, Mich. Agr. Expt. Sta. Spec. Bui. 196, p. 14. CHRISTOWE, M. 1946. GREEN MOUNTAIN SAP. Farm Quart. 1 (4): 38- 43, 134-1.35, illus. COLLINGWOOD, G. H., and COPE, J. A. 1938. MAPLE SUGAR AND SIRUP. N.Y. Agr. Col. (Cor- nell) Ext. Bui. 397, .32 pp., illus. (Rev. 1944.) Cope. J. A. 1949. DEPTH OF TAPPING IN RELATION TO YIELD OF MAPLE SAP. Jour. Forestry 47: 478-480. 1949. MAPLE SIRUP AND SUGAR. N.Y. Agr. Col. (Cor- nell) Ext. Bui. 397, .32 pp., illus. (Rev.) [First printed 1938; the revision reprinted 1952.1 Dambach, C. a. 1944. comparative productiveness of adjacent grazed and ungrazed sugar-maple WOODS. Jour. Forestry 42: 164-168. illus. Dansereau, p. 1944. L'INDUSTRIE DE L'ERABLE. Universite de Montreal, Institut de Biologie (Secretariat de la Province de Quebec, Service de Biogeogra- phie). 44 pp., illus. [Quebec. I [Processed.] Edson, H. a., Jones, C. H., and Carpenter, C. W. 1912. MICRO-ORGANISMS OF MAPLE SAP. Vt. Agr. Expt. Sta. Bui. 167: [3211-610, illus. Fabian, F. W., and Buskirk, H. H. 1935. AEROBACTER AEROGENES AS A CAUSE OF ROPINESS IN MAPLE SIRUP. Indus, and Engin. Chem., Indus. Ed., 27: .349-450. Finlay, M. C. 11934.] our american maples and some others. 19 pp., illus. New York. GILMAN, W. 1949. MAPLE— THE MYSTERY TREE. 42: 119-122, illus. GOING, M. 1917. Nature Mag. Canad. For- IN THE MAPLE SUGAR SEASON. estry Jour. 13: 992-994, illus. GROSE, L. R. 1920. MAPLE SUGAR IN COLONIAL TIMES. Amer. Forests 26: 689-690. Hayward, F. W. 1946. THE STORAGE OF MAPLE SIRUP. N.Y. State Agr. Expt. sta. Bui. 719, 8 pp., illus. and PedeRSON, C. S. 1946. SOME FACTORS CAUSING DARK-COLORED MA- PLE SIRUP. N.Y. State Agr. Expt. Sta. Bui. 718, 14 pp.. illus. Herbert, P. A. 1924. the weather and MAPLE SUGAR PRODUC- TION. Mich. Agr. Expt. Sta. Quart. Bui. 7: 60- 62, illus. Herr, C. S. 1938. maple syrup and sugar production in NEW HAMPSraRE. N.H. Univ. lAgr.l Ext. Bui. 52, 20 pp., illus. Hills, J. L. 1904. the maple sap flow. Vt. Agr. Expt. Sta. Bui. 105: [1931-222, illus. Hitchcock, J. A. 1928. economics of the farm manufacture of maple syrup and sugar. Vt. Agr. Expt. Sta. Bui. 285. 96 pp., illus. 1929. COST AND PROFIT IN THE SUGAR ORCHARD. Agr. Expt. Sta. Bui. 292, 19 pp., illus. 1937. Vt. THE GRAZING OF MAPLE SUGAR ORCHARDS. Vt. Agr. Expt. Sta. Bui. 414, 14 pp., illus. HUFFMAN, R. E., DeVault, S. H., and Coddington, J. W. 1940. an economic study of THE MAPLE PRODUCTS industry in GARRETT COUNTY, MAR^XAND. Md. Agr. Expt. Sta. Bui. 431. pp. 16.5-215, illus. MAPLE SIRUP PRODUCERS MANUAL 135 HuTCHiNs, Mrs. H. 1900. PIONEERING |IN MICHIGAN) — GATHERING SAI' AND GOING TO MILL. (A poem.) In (Mich. Hist. Comm.,1 [Mich.) Hist. Collect. (1897-9S) 28: 638-640. (Collections and Researches made by Michigan Pioneer and Historical Soci- ety.) Jones, c. H. 1938. the exclusion of lead from maple sap. (PROGRESS REPORT.) Vt. Agr. Expt. Sta. Bui. 439, 7 pp. and Bradlee, J. L. 1933. the carbohydrate CONTENTS OF THE MAPLE TREE. Vt. Agr. Expt. Sta. Bui. 358, 147 pp., illus. Kelley, M. C. 1933. SAP, SUGAR AND SHEEPSKINS. Amer. Forests 39: 114-115, 144, illus. 1936. SAVING THE SUGAR ORCHARD. Amer. Forests 42: 221, 242, illus. MclNTYRE, A. C. 1932. THE MAPLE PRODUCTS INDUSTRY OF PENN- SYLVANIA. Pa. Agr. Expt. Sta. Bui. 280, 47 pp., illus. McKay, A. W. 1922. MARKETING VERMONT MAPLE-SAP PRODUCTS. Vt. Agr. Expt. Sta. Bui. 227, 48 pp., illus. Marvin, J. W., and Erickson, R. O. 1956. A STATISTICAL EVALUATION OF SOME OF THE FACTORS RESPONSIBLE FOR THE FLOW OF SAP FROM THE SUGAR MAPLE. Plant Physiol. 31: 57-61. [Maryland University Agricultural Extension Service and Garrett County Maple Producers Association.) 1931. MAPLE SUGAR AND SIRUP RECIPES. Md. Univ. [Agr.l Ext. Cir. 87, 9 pp. Moore, H. R., Baker R. H., and Diller, O. D. 1948. THE FARM SUGAR BUSH. Ohio Farm and Home Res. [Ohio Expt. Sta.[ 33 (251): 40-45, illus. Morrow, r. r. 1952. consistency in sweetness and flow of MAPLE SAP. Jour. Forestry 50: 130-131. MURPHEY, F. T. 1937. THE MAPLE SYRUP CROP. Pa. State Col. Ext. Cir. 186, 28 pp., illus. 1947. MAKING MAPLE SYRUP. Pa. State Col. Ext. Cir 310, 36 pp., illus. Nearing, H., and NEARING, S. [1950.1 THE MAPLE SUGAR BOOK. 271 pp., illus. New York and Toronto. ORMSBEE, C. O. 1920. EVERY STEP IN MAPLE SUGAR MAKING. Rural New Yorker 79: 343-344, 409, 519-520, 576, 625, illus. 1923. THE MAPLE SUGAR INDUSTRY. THE TREE THAT MADE VERMONT FAMOUS, AND HOW ITS DE- LECTABLE JUICE IS HARVESTED. Sci. Amer. 129: 176, 214-215, illus. ORTON, V. 1941. SUGARING. Sat. Evening Post 213 (38): [14]- 15, 104, 106, 108-109, illus. PEARL, M. 1952. VERMONT MAPLE RECIPES. 87 pp., illus. Bur- lington, Vt. Peffer, E. L., and BLAIR, M. G. 1949. TESTING of hydrometers. [U.S.I Natl. Bur. Standards Cir. 477. 9 pp., illus. Pennsylvania Department of Forests and Waters. Division of Forest Research. 1952. "common trees" of PENNS'i'LVANIA. 55 pp., illus. [Harrisburg.) ROBBINS, P. W. 1944. SMOKE IN THE SUGAR BUSH. Counti-y Gent. 114(2): 22, 25-26, illus. 1949. PRODUCTION OF MAPLE SYRUP IN MICHIGAN. Mich. Agr. Expt. Sta. Cir. Bui. 213, 28 pp., illus. SCHULER, L., and SHERMAN, R. W. [n. d.) MAPLE SIRUP MARKETING IN GEAUGA COUNTY, OHIO. Ohio State Univ.. Dept. Agr. Econ. and Rural Sociol. AE 327, 16 pp. Science 98: Country SEARS, P. B. 1943. GRAZING VERSUS MAPLE SYRUP. 8,3-84. SMITH, R. H. 1919. TAPPING NATURE'S SUGAR BUSH. Cfent. 84 (4): 13, 63-64, illus. Snell, J. F. 1913. THE ANALYSIS OF MAPLE PRODUCTS. I. AN ELECTRICAL CONDUCTIVITY TEST FOR PURITY OF MAPLE SYRUP. Jour. Indus, and Engin. Chem. 5: 740-747, illus. 1916. THE ANALYSIS OF MAPLE PRODUCTS. V. MIS- CELLANEOUS OBSERVATIONS ON MAPLE SYRUP [TO FIND] NEW METHODS OF DETECTING ADUL- TERATION. Jour. Indus, and Engin. Chem. 8: 144-148. and ScOTT, J. M. 1914. THE ANALYSIS OF MAPLE PRODUCTS. III. THE RANGE OF VARIATION OF ANALYTICAL VALUES IN GENUINE MAPLE SYRUPS. Jour. Indus, and Engin. Chem. 6: 216-222. SPENCER, J. B. 1923. THE MAPLE SUGAR INDUSTRY IN CANADA. (THIRD EDITION.) Canada Dept. Agr. Bui. (n.s.) 30, 43 pp., illus. sy, a. p. 1908. HISTORY, MANUFACTURE AND ANALYSIS OF MAPLE PRODUCTS. Franklin Inst. Jour. 166: 249-280, 321-352, 43.3-445, illus. 136 AGRICULTURK HANDBOOK i:54, U.S. DEPT. OF AGRICULTURE TOWLE, D. S. 1946. SAP WEATHKR. Anier. Mus. Nat. Hist., Nat. Hist. 55: IU0I-U2. illus. Vermont Department of Agriculture. 1941. \ermont maple sugar and syrup. vt. Dept. Afcr. Bui. .38, 41 pp., illus. (Rev.) WEBBER, L. E., and SeeLEY, L. E. 1950. OPERATION OF MAPLE SAP EVAPORATORS US- ING OIL BURNERS. N.H. Enpin. Expt. Sta. Engin. Pub. 9, 7 pp., illus. _ WEIR, J. G. 1982. CARE OF THE SUGAR BUSH. Vt. Agr. Col. Ext. Cir. 71, 15 pp., illus. 1933. SUGGESTIONS FOR MAKING HIGH QUALITY MA- PLE SYRUP. Vt. Agr. Col. Ext. Cir. 73, 16 pp.. WILLITS, C. O. .- 19.38. THE PAINTING OF SAP BUCKETS AND OTHER EQUIPMENT USED IN THE PRODUCTION OF MA- PLE SYRUP. N.Y. State Agr. Expt. Sta. Cir. 182, 4 pp. and TRESSLER, C. J., JR. 1939. THE PREPARATION AND PAINTING OF MAPLE- SUGAR- PRODUCING EQUIPMENT. Jour. Agr. Res. 59: 151-158, illus. WINCH, F. E. 11954.1 TAP YOUR TREES. N.Y. State Col. Agr. ICornelll Ext. Serv. |5| p. folder, illus. (Coop. Ext. Work in Agr. and Home Econ.) Woods, J. B. 1945. MAPLE SUGAR OR MAPLE LOGS? ests 51: 544-.547, illus. Amer. For- ■& U..S. GOVERNMENT PRINTING OFFICE: 197B O— 597-10!