Why Goat's Milk Can't Be Made Into Mozzarella

Flavor aside, we wanted to dig deeper into how the type of milk influences the texture, color, and richness of a cheese. To that end we procured raw cow's milk from Lawton's Family Farm in Foxboro, Massachusetts, and raw goat's milk from The Herb Hill Micro Dairy in Andover, Massachusetts, and made a mozzarella-style stretched cheese from each.

We used an identical recipe for both the goat's milk and cow's milk, based on precise temperatures and pH. We added thermophilic cheese culture to 82-degree milk, which we ripened at 90 degrees until the pH dropped. We added liquid animal rennet, stirred, and let the milk coagulate. We cut the mass into curds, let them ripen in the whey, drained them, cut them, and stretched them in whey at 175 degrees.

For the cow's milk: We noticed that after coagulating, some fat escaped from the milk and rose to the surface of the whey. The final curds easily stretched to over a foot and resulted in a springy, off-white, mild-tasting mozzarella.

For the goat's milk: We didn't notice any fat on the surface of the whey after coagulating. The final curds stretched up to 6 inches, but broke if pulled any further. The mozzarella was soft, pure white, and tasted distinctly of goat milk.

Goat's milk differs from cow's milk in a few important ways. Unlike cow's milk fat, the fat in goat's milk doesn't flocculate (or separate from the rest of the milk and rise to the surface). This helps explains why the fat stayed in the curd mass for the goat's milk, but separated in the cow's milk. A compound found in fat is also the culprit for the color difference. Goat's milk fat, unlike cow's milk fat, does not contain carotene (the compound that makes carrots orange) so the milk (and cheese) remains pearly white.

What about the stretching ability of the cheeses? Here things get a bit more complicated. The important milk protein when it comes to cheese making is casein. Goat's milk contains less casein (2.1 to 2.4 percent by weight) than cow's milk (2.6 to 2.7 percent by weight), and that small difference has a big impact on the milk's ability to coagulate into a firm gel. In addition, the goat's milk we used was a mixture from three different breeds: Nubian, Toggenburg, and LaMancha. Research has shown that some goats lack a functional gene for a certain form of casein, alpha-s1-casein, which can affect the curd-forming properties of their milk. Milk from Nubian goats contains higher levels of alpha-s1-casein (and is therefore thought to make better cheese) than milk from Toggenburgs. We suspect that using all Nubian goat's milk would result in a mozzarella that could stretch more similarly to the cow's milk mozzarella. The cow's milk we used came from a herd of mostly Ayrshire cattle with a few Holsteins—both breeds with a long history of milk production for quality cheese making.