DAIRY PRODUCTS 223
method as in milk, using about 5 gm of sample, or by burning the
casein from the residue from the indirect fat determination,
calculating the loss in weight as casein. The temperature is
kept just below redness (to avoid volatilizing salt) until the
residue is white. A muffle furnace, heated to 600°, is suitable
for this ignition.
Salt.—Salt is added to improve the keeping quality and the
taste of butter. The amount added ranges from 2 to 6 per cent.
Salt is determined by adding a standard solution of silver nitrate
to the water extract of the butter, using potassium chromate as
an indicator. (See page 52, Part I.)
f
Determination of Salt.—In a small counterpoised beaker place about 10
gm of butter, secured from various parts of the prepared sample, and weigh
to the third decimal place. Add about 20 cc of boiling water and when the
butter is melted transfer to a small separatory funnel of about 50-cc capacity. P
Shake the mixture thoroughly and allow the fat to come to the top of the || |
water. Draw off the water layer into a 250-cc volumetric flask, guarding |||
carefully against the passing of any fat globules. Repeat the extraction
with hot water ten to fifteen times. Cool the washings to 20°, dilute to the
mark on the flask, mix thoroughly and pipette 25 cc of the liquid into a
casserole for the determination of salt. Titrate with twentieth-normal
silver nitrate solution, using 1 cc of neutral 5-per cent potassium chromate
solution as indicator.
Examination of Butter Fat.—The composition of butter fat is
quite different from that of other fats in that it contains a larger
proportion of the glycerides of fatty acids of low molecular
weight, particularly of butyric acid.
In the following table by Brown,1 the average composition of
butter fat is expressed in terms of the various glycerides, also of
free acids obtainable by hydrolysis.
1 /. Am. Chem. 3oc., 21, 807 (1899).