This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
A simple home-made ice cream may be made with cream, sugar, and flavoring. Flavoring is added to increase the palatability. The flavoring may be extracts, fruit, or nuts. Sometimes egg is added to home-made ice cream. Cream containing 17 to 20 per cent butter fat, or if not homogenized, 22 per cent fat, gives a good home-made ice cream. Washburn states that the weight of sugar added may be one-sixth of the weight of the cream. Three-fourths of a cup of sugar to a quart of cream gives about this proportion, and this produces an average sweetness. The serum solids usually average about 6 per cent in home-made ice cream.
Sommer states that a good commercial ice cream is obtained with the following proportions:
Serum solids 10.0
Gelatin 0.25 to 0.50
Egg yolk solids 0.50
Total solids 39.25 to 39.50%
Sommer also states that a richer ice cream has not proved generally successful because of the higher cost, but is preferred by many consumers. In the richer cream the fat is increased to 16 per cent and the serum solids reduced to 8 per cent. Although Sommer recommends the egg yolk solids, many manufacturers omit them. Gelatin, called a binder, is used to prevent coarse crystallization. Commercial ice cream must have condensed-milk or dry-milk products added to raise the serum solids to 8 or 10 per cent.
The milk solids include the butter fat, the milk proteins, the milk sugar, and the ash; serum solids exclude the fat; total solids of ice cream include the milk solids and the added sugar. The total solids vary, but Sommer states they should not exceed 41 per cent. Each of the ingredients of the milk and also the added sugar has an effect on the body and the texture of the ice cream. The ingredients likewise affect the flavor.