Page:The story of milk.djvu/74

 cream four times as rich as the milk, a "16% cream." So out of 100 lbs. of milk we can take 12-1/2 lbs. (1/8) of 32% cream, 25 lbs. (1/4) of 16% cream, etc.

Although the skim milk is really valuable as a food, it is worth but little commercially; the cream containing the butter-fat is the expensive part of the milk, and we must be prepared to pay for the cream all that the milk would have cost.

Percentage of Butter-Fat.—The "richness" of cream or milk and their value depend upon the amount of butter-fat in them. So cream or milk is often called "30% cream" or "20% cream" or "4% milk" according as 30% or 20% or 4% of the fluid is butter-fat; 30% cream is quite rich; ordinary market cream varies between 18% and 40%, though it may fall below 18%, or it may be sold as a very expensive article as high as 60%. Rich milk may contain more than 6% of butter-fat and skim milk less than 0.1 of one per cent. The average for good whole milk is between 3% and 4-1/2%.

For a long time scientists and scientific dairymen were the only ones to speak of milk and cream in terms of percentage of butter-fat. Now, however, people are beginning to realize how valuable a part of the milk the butter-fat is and are paying more attention to the actual percentage of butter-fat in the cream or milk they use. So it is no longer unusual to see a dairyman advertise cream of a certain percentage or to hear a housewife ask for it specifically.

Standardizing Cream.—For ice cream or for preparing modified milk for babies, it is often desirable to dilute rich cream to a certain lower standard. The following simple steps can be taken to find out how much milk to add for diluting: