Try a quick experiment. Pour three different milks, whole, 2 percent, and skim, into three clear glasses, and hold them to the light. They vary considerably in their appearance, don't they? The whole milk is more opaque, is a creamier white, and looks thicker than the other two. The skim milk has some translucence to it, and seems to have a hint of blue. It swirls like water and looks thin. The two-percent milk is in between these two in color and density.

Now imagine pouring three new glasses: one cow's milk, one sheep's milk, and one goat's milk. All three not only taste different, they also have different amounts of fat and protein, and behave differently when made into cheese.

How the Animals Differ

Cow's, goat's, and sheep's milk are each made up of water, fat, protein, lactose, and minerals. The first and most important differences between the three are in the percentages of these ingredients, particularly fat and protein. On average, sheep's milk is higher in fat and protein than cow's and goat's milk, goat's milk is lower in protein than cow's milk, and cow's and goat's milk have about the same percentage of fat.

Water, Fat, and Protein in Animal Milk

Animal	Water	Fat	Protein
Cow	87 percent	3–5 percent	3–4 percent
Goat	89 percent	3–4 percent	3–3.5 percent
Sheep	83 percent	6 percent	5–6 percent

Milk Protein

During cheese making, much of the water is drained from milk, and most of the fat and protein stay with the curds. The curds are what make the cheese, and the higher the percentage of protein, the firmer the curds are and the faster they coagulate. This means that more cheese can be made from milk with high protein counts than from milk with low protein counts. So, sheep's milk, at 5–6 percent protein, makes up to twice the amount of cheese as cow's or goat's milk.

The type of protein is also important. Milk protein is casein, and at the molecular level, there are alpha-casein and beta-casein molecules. These molecules coagulate differently. Alpha-casein molecules are firmer and more solid, while beta-casein molecules are more fragile. Not only does this contribute to how much cheese can be made from a set amount of milk, but it also contributes to the texture of the curd. Beta-casein molecules produce a fragile curd that is flakier in texture.

It turns out that sheep's and cow's milk are both high in alpha-casein molecules, while goat's milk is higher in beta-casein molecules. This is partly why it takes more goat's milk to make cheese and why goat's-milk cheese has some flakiness to its texture.

Milk Fat

The type of fat in milk is also important. Different fats create different aromas and flavors, and these three animal milks have different fat molecules, which contribute to different tastes. For example, fat molecules in sheep's and goat's milk are mostly short fatty acids, which create strong aromas and flavors. Cow's milk is mostly made up of long chains of fatty acids that are sweeter and milder in flavor. And cow's milk is the only one of the three that contains cryoglobulin, which is a sticky whey protein that effectively creates the clusters of fat that cream is made from.

As milk cools from the temperature of the cow, these fat clusters rise to the surface and can be skimmed off for cream, or reincorporated into the milk. When reincorporated, the milk is whole, and contains all its original butterfat. Neither sheep's nor goat's milk can be skimmed in this way because without cryoglobulins, the fat rises to the surface very slowly, over several days, and the milk would likely spoil before the cream could be skimmed.

Milk Production

Finally, one of the most important differences between cows, goats, and sheep is how much milk they produce. On average, a cow will produce from eight to 20 quarts of milk per day. A goat will produce three to four and a half quarts per day, and a sheep will produce about one quart of milk per day. With cows producing two to four times as much milk as goats, and eight to 20 times as much milk as sheep, it's easy to see why cow's-milk cheese is the most plentiful, followed by goat's-milk cheese.

So far, you've read about cows, goats, and sheep in general terms, but different breeds also differ in percentages of fat, types of protein, and production of milk they usually offer. For example, on average, Holstein cows produce more milk per day than Jersey cows, but Jersey cow milk has a higher fat content than Holstein cow milk. Among the goat breeds, Nubians and La Mancha goats have higher butterfat, but they produce about the same amount of milk per day as other milking goat breeds.

Animal Husbandry

Animal husbandry, the agricultural practice of breeding and raising livestock, plays a very important role in milk production. Generally speaking, healthy, content animals produce nutritious, flavorful milk, and unhealthy or discontented animals produce milk that is inferior in nutrition and flavor.

Animals can be pasture fed, grain fed, and silage fed, and some diets are supplemented with vitamins, minerals, antibiotics, and hormones. Unless animals are moved, pastures are available only at certain times of the year, so often pasture-fed animals also eat grains, and many farmers grow grain and create their own mixture of grains to supplement lean pasture months. Silage is made up of edible farming byproducts and can range from crushed grape skins to a mixture of grains, seeds, grasses, and other byproducts. Animals without access to pastures are usually fed a combination of grain, silage, and supplements of vitamins and minerals. All of these diets directly influence the flavor and nutritional content of cheese.

Living conditions and terrain also affect the milk. Animals under stress, that is, under conditions that require them to work too hard for their food, will produce less milk with fewer vitamins and minerals. Where food is readily available and terrain is natural to the animal's habitat (pastureland for cows, hillsides for sheep, and either or both for goats), the milk is more plentiful and more nutritious. Sweet grasses and spring flowers can be tasted in the milk and then the cheese, as can the aromas of crowded barnyard conditions.

Finally, milk is also affected by the seasons. As animals move in and out of lactation and graze on spring, summer, fall, and winter diets, the amount of fat and protein changes dramatically. Fat levels drop in summer, rise in the fall, and peak in early winter. Proteins do the same, so cheese made from fall milk will be higher in butterfat and protein than cheese made from milk in the summer.