I had the privilege of talking to the young men and women in the biotech program at Shawnee Mission West High School recently. They have a small section in their studies that explores the science of cheese. I was asked to talk about cheese with three classes after they had done a few experiments dealing with coagulating milk.
Although the first class was a little timid at 7:30 a.m., the kids were very interested in cheese and the cheese-making process. Their experiment had to do with enzymatic coagulation. The young scientists and cheesemakers added animal rennet to one vat of cow’s milk, and to another they added chymosin.
They looked to see whether there were any noticeable differences in the two. It seemed that each class found that the chymosin worked best when it came to coagulating milk. All things being equal, it consistently set the milk firmer and quicker than the rennet.
There are several ways to coagulate milk for cheese making. Enzymatic coagulation is the most common method in cheese making, especially when making harder cheeses. Cheeses like cheddar, Gouda and Gruyere are all coagulated using enzymes. Rennet is an enzyme found in the stomachs of young ruminant animals. It helps them digest their mother’s milk.
Chymosin is basically the most active and plentiful enzyme found in the abomasa stomach of those animals. Today it is a genetically modified organism made by crossing cow chymosin genes with a fungus or yeast. The resulting pure chymosin is often labeled as “vegetarian rennet.”
Paul Kindstedt, noted author of many books on cheese and cheese science, points to three different kinds of coagulation in the cheese- making process. They are enzymatic coagulation, acid coagulation and acid/heat coagulation.
Many soft cheeses undergo acid coagulation. They are sometimes referred to as lactic-style cheeses. Acid coagulation is brought about by lactic acid bacteria that are either present in the milk or added to the milk.
They feed on the lactose (milk sugars) in the milk, and this begins to lower the pH of the milk and in turn raises the acidity of the milk. The rise in acidity eventually coagulates the milk.
This rise in acidity actually goes a long way in ensuring the safety of the finished cheese. If the pH levels are sufficiently low in the cheese, other harmful bacteria are not able to gain a foothold in the cheese, and the good lactic acid bacteria thrive in the environment.
The last kind of coagulation is acid/heat coagulation. This kind of coagulation is achieved by heating the milk and then adding an acid to the milk. Although the lactic acid bacteria can be used, the most common cheeses that use the acid/heat combination use things like vinegar or lemon juice.
If you have ever tried your hand at homemade ricotta, you probably noticed this heat/acid combo in the recipe. Another classic cheese made this way is queso blanco.
Acid/heat coagulated cheeses are some of the easiest cheeses to make at home. There are no real specialized ingredients and tools needed for them. Click here for an easy ricotta recipe.
Lincoln Broadbooks loves cheese. He is one of the first cheesemongers in the United States and Canada to become an American Cheese Society-certified cheese professional. He is the manager and buyer for the Better Cheddar in Prairie Village. You can find him on Twitter @LincolnBbooks and on Instagram @lincycheese.