Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. aad TED STATES DEPARTMENT OF AGRICUL B Washington, D. C. v February 28, 1923 THE FREEZING TEMPERATURES OF SOME FRUITS, VEGETABLES, AND CUT FLOWERS. 3 By R. C. Wricut, Physiologist, and GEORGE F. Taytor, Associate Physicist, Office of Horticultural and Pomological Investigations, Bureau of Plant Industry. CONTENTS. ‘ Page | Page. EMELOMUEtIOM EE we ee 1 | Freezing points of cut flowers.............-.- 7 Breezine pomts' OL irulbs:. -- 2s s- +o eee SP EVCCADIDMIAGIOINS. <2 2 eee ese amet ae oe ee 7 Freezing points of vegetables.............--: 5 | INTRODUCTION. There is an ever-increasing demand from those interested in the rowing, shipping, and handling of produce for exact data on the seein points, or the temperatures at which various products reeze. The extent of damage due to the freezing of produce in transit naturally varies from year to year, but it is usually very heavy, ageregating frequently several hundreds of thousands of dollars during a year. ‘This in general applies not only to such products as apples and potatoes, most of which are grown in the North and har- _ vested and shipped in the late fall and winter, but to products which are grown in the South and Southwest during the winter and shipped to the northern markets. This latter group includes citrus fruits, strawberries, tomatoes, lettuce, string beans, cabbage, cauliflower, egeplant, etc. Cars of these food products often leave the shipping point under refrigeration and in 24 to 36 hours may pass into a zone of freezing temperatures. As they approach the more northern markets they may be exposed to temperatures ranging several degrees below zero. Under some conditions when harvested in warm weather some of these products may be precooled—that is, rapidly cooled to a refrigerating temperature, either immediately before or directly after they are placed in the car for shipment, in order to delay maturity and consequent deterioration. Where precooling is practiced, it is, of course, very important to know the temperatures to which the product can be lowered with absolute safety. NoTe.—This bulietin gives the results of a portion of the work carried on under the projects ‘‘ Factors affecting the storage life of vegetables”’ and “‘ Factors affecting the storage life of fruits.” 21854—23 2 BULLETIN 1133, U. S. DEPARTMENT OF AGRICULTURE. _ Knowledge of the exact freezing points of fruits and vegetables is of importance also to the commercial cold-storage man. In most cases fruits and vegetables other than dried or prepared products when placed in cold storage are alive, and the prahletn is to keep them alive and healthy throughout their storage period. Since various fruits and vegetables freeze at different temperatures, there is more or less doubt in the minds of those interested as to the proper and safe temperatures at which to hold these various products in storage. One of the problems in the storage of many of these products is to hold them at a temperature low enough to slow down the living processes in order to prolong their storage life and yet not allow them to be damaged by actual freezing. Of course, some products, such as berries, may be purposely kept at a freezing temperature and used at once on thawing out, but this subject comes under the head of freezing storage and will not be discussed here. It is therefore essential in commercial work of this kind that accurate data be at hand on the temperatures to which these products can be exposed without injuring their keeping qualities or market value. It should be borne in mind, however, that freezing or fgeezing injury does not always occur when fruit or vegetable products are exposed to temperatures at or below their true freezing points. This is shown in the studies on Irish potatoes reported in a previous publication,} where tubers were cooled as much as 10° I’. below their freezing points and again warmed without apparent injury. The commonly known fact that some kinds of products may be actually frozen and then thawed out under certain conditions with no apparent injurious effects constitutes further evidence on this point. On the other hand, some commodities are injured if stored at temperatures well above their actual freezing points. It is evident, therefore, that tempera- tures just above the freezing point can not be regarded as safe for | all types or varieties of fruits and vegetables. It is also noticeable that there are some variations in the freezing points of fruits or vegetables of the same variety and from the same lot, as is shown in the tables that follow. Furthermore, it is quite probable that different individuals of the same variety and strain when grown under different conditions will have somewhat different average freezing points. Attention is therefore called to the fact that the freezing points given in the following tables should be considered as danger points; that is, at ornear these temperatures, either above or below them, there is a possibility that the product will be in danger of injury by freezing if exposed for a sufficient length of time. These are temperatures at which it is unsafe to hold produce which is to be used for food if it is desired to maintain it for any length of time in a living condition. The determinations of the freezing points of a number of fruits and vegetables have been made by the Bureau of Plant Industry in connection with its cold-storage investigations. By freezing point is meant the temperature at which ice crystals begin to form within the product, either fruit or vegetable. Some 10,000 of these determinations have already been made on many varieties of commercially grown fruits and vegetables, and 1 Wright, R. C., and Taylor, George F. Freezing injury to potatoes when undercooled. U.S. Dept. Agr. Bul. 916, 15 p., 1 fig., 1 pl. 1921. Literature cited, p. 15. FREEZING TEMPERATURES OF FRUITS, VEGETABLES, AND FLOWERS. 3 work is being continued. It has been found in some cases that the freezing points of some varieties are liable to slight variations from year to year, even though the same strain grown in the same locality is used. These variations, however, are probably of more importance in the study of the exact causes and results of freezing injury than from the point of view of the commercial cold-storage and produce man, for the variation of a fraction of a degree hardly warrants ‘any change in the treatment of the produce. It therefore seems advisable to publish the results of these investigations from time to time as obtained, because of the need for such information and because there is no comprehensive publication on the subject. The method of determining freezing points has been described in former papers,” and a repetition of this description is not required here. ) FREEZING POINTS OF FRUITS. Where several varieties of one kind of fruit were investigated the results are given separately to allow comparisons to be made. All temperatures are expressed in degrees Fahrenheit. Apples.—Freezing-point determinations were made for a number of authentic varieties of summer or early apples and of fall and winter varieties, most of which were grown on the Arlington Experi- ment Farm. The tabulated results given by varieties are shown in Table 1. These results show considerable varietal differences among both summer and winter apples. The average of all summer varieties is practically the same as that of winter varieties, the former being 28.44° I’. while the latter is 28.51° F. These results show very little difference between the freezing points of eastern- grown and western-grown fruit. Cherries.—Freezing-point determinations were made for seven varieties of cherries grown on the Arlington Experiment Farm. The average of all varieties was 27.81° F. (Table 1.) Grapes.—Results were obtained from the freezing of seven varieties of grapes, all of which were grown on the Arlington Experiment Farm. The average freezing point of all the varieties was 28.16° F. (Table 1.) Oranges.—The average freezing point of the six varieties of oranges studied was 28.03° F. (Table 1.) Peaches.—Freezing-point determinations were made for 11 va- rieties of peaches grown near Leesburg, Va.,in the Loudoun orchard of the American Fruit Growers (Inc.). Peaches in the hard-ripe stage were utilized for these tests. The average freezing point of all varieties when hard ripe was found to be 29.41° F. (Table 1.) Plums.—Freezing points were obtained for four varieties of plums that were grown in California and purchased on the market and for one variety (Red June) grown at the Arlington Experiment Farm. The variety with the lowest freezing point is Tragedy, with a freezing temperature of 27.21° F. The average freezing point of all varieties iS 25155 0H ( Table 1.) 2 Taylor, George F. Some improvements on the needle type thermocouple for low-temperature work. In Jour. Ind. and Eng. Chem., v. 12, p. 797-798, 1 fig. 1920. Wright, R. C., and Harvey, R. B. The freezing point of potatoes as determined by the thermoelectric method. U.S. Dent. Agr. Bul. 895, 7p., 1 fig. 1921. Bibliographical footnotes. Wright, R. C., and Taylor, George F. Freezing injury to potatoes when undercooled. U.S. Dept. Agr. Bul. 916, 15 p., 1 fig., 1 pl. 1921. Literature cited, p. 15. BULLETIN 1133, U. 5S. DEPARTMENT OF AGRICULTURE, F TABLE 1.—Average and extreme freezing points of fruits. Fruit and varieties. Temperatures (° F.) Extremes. Aver. age. | Mini- | Maxi- mum. mum. Apples, summer varieties: Yellow Transparent... Red Astrachan....... Barly eRip esse ees ese Redwnunet sess ses 4 Sweitz Cf-..---------- Average (not in- cluding the crab ApPDPlC) ese Apples, fall and winter varieties, eastern grown: Winesap........ uae Yellow Newtown....- York Imperial........ INVCLA GO Se ese ore Se Apples, fall and winter varieties, western grown: Rome Beauty...---.-- Esopus (ECR) Winesap.. heen Cherries: Early Richmond..... Montmorency......-- StaMedard ee oe Bigarreau (unknown VMarLeby seats a esse AVeracess eee! Grapes: New Concord.....--- PACT OSTA esis pare Dracut Amber....... Moores Early.......-- Cantivator. S26. -2s2- Campbell (black)....- Mericadeless252% 255 a: Averages 25. 22.5% Oranges: RIN eCap plese cree aaaee Fruit and varieties. 27.72 | 27.29] 28.16 28.58 | 28.25 | 28.70 29.18 | 28.82] 29.47 29.59 | 29.29 | 29.71 J738 peat 2) 27. Al 28.46 | 27.93 | 28.03 28.83 | 28.49 | 29.00 27.81 | 27.60 | 28.49 26.70 | 26.62 | 26.76 28.44 | 28.12 28. 62 28.36 | 27.98 | 28.86 98.55 | 28.26 | 29.05 28.60 | 282€| 29.05 98.35 | 28.02| 28.72 98.92 | 28.72| 29.38 98.69 | 28.26 | 29.05 98.24 | 27.93 | 28.35 98.53 | 28.20] 28.92 27.94 | 27.60 | 28.35 98.10 | 27.79 | 28.58 28.09 | 27.60 | 28.58 28.16 | 27.95 | 28.50 27.65 | 27.37 | 28.21 26.88 | 26.76 | 27.69 27.83 | 27.83 | 27.83 27.81 | 27.56! 28.25 28.39 | 27.93 | 28.68 28.21 | 27.83 | 28.63 27.88 | 27.77 | 28.10 98.28 | 28.15 | 28,62 27.86 | 27.14 | - 28.05 27.96 | 27.77 | 28.60 28.54 | 28.40| 28.54 28.16 | 27.85 | 28.37 28.64 | 28.34] 28.82 27.72 | 27.60 | 27.83 28.20 | 28.10| 28.43 Oranges—Continued. Washington “avel... Valencia (California) - Satsuma (Owari va- LOL VA) ee eee eee we AAS nes ies le vat