Lactose and rennet are two substances deeply involved in dairy foods and their production. Conventional rennet originates in the stomachs of cows and is used in cheese manufacturing, while lactose is a natural sugar component of animal milk and derivative dairy products. In modern times, rennet sourcing has diversified to non-animal sources, while options that enable lactose-intolerant people to enjoy dairy foods continue to proliferate.
Lactose
Lactose is a natural sugar found in all animal milk. Its concentration varies by species and is highest in human milk, averaging near 7 percent, while goat, sheep and cow milk average between 4 and 5 percent. Many processed dairy foods, such as ice cream and hard cheese, can have less lactose than the milk from which they're derived, sometimes near zero for certain aged cheeses. Some dairy products, however, such as ice milk or evaporated milk, can carry more lactose than their plain milk precursor.
Lactose Intolerance
Lactose sugar is broken down by the lactase enzyme. The majority of human adults are "lactose intolerant," meaning that the cells of their small intestine don't produce significant lactase. As a result, their digestive systems are unable to break down lactose and absorb it as usable energy. When eating dairy foods, the undigested lactose sugar can then move through the gastrointestinal tract, often resulting in gas, cramping and other symptoms. Lactose intolerance is a digestive issue of the gastrointestinal tract, and separate from milk allergy, which can cause a systemwide autoimmune response. A milk allergy generally requires avoidance of all milk-containing products, while lactose intolerance usually permits consumption of certain dairy foods.
Rennet and Cheese
Rennet is a collection of enzymes traditionally derived from the inner stomach lining of cows and young calves. The active enzymes in rennet are important to cheesemaking, causing milk to coagulate and curdle into the solids that later become cheese. Just a teaspoon of liquid rennet is adequate to coagulate five gallons of milk. Since the 1990s, a substantial amount of rennet has been produced from vegetable sources and genetically engineered bacteria, eliminating the need for animal rennet in many cheeses. European cheese makers, however, generally continue to use animal-sourced rennet.
Rennet's Effect on Lactose in Cheeses
While rennet doesn't break down lactose, the enzymes' curdling effects help separate lactose out of the milk solids that are turned into hard cheeses. As a water-soluble molecule, lactose remains dissolved in the whey, or milk liquid, when rennet begins to coagulate milk solids in the initial stages of cheese making. The more thoroughly the solids and whey are separated, the less lactose remains in the finished cheese. Some cheese makers also add specific bacteria to the coagulating solids that actively break down the lactose, reducing its concentration even further.
Dealing with Lactose Intolerance
If you have lactose intolerance, without a milk allergy, there are many options for continuing to enjoy dairy products and their nutritive benefits. Ask your doctor and grocer about special dairy milk brands that contain added lactase enzymes and almost no lactose sugar. You may also find lactose-free versions of cheeses, ice creams and other common dairy foods. Lactase enzyme supplement tablets are taken immediately before dairy foods and break down lactose sugars in the stomach before they can cause gastrointestinal upset. Also, determine the extent of your lactose intolerance. You may only need lactase supplements before a larger dairy meal or drinking straight milk. There are also some non-dairy foods, such as soy or rice milk, that provide some of the vitamins and minerals of dairy milk without the lactose sugar.
References
- National Institutes of Health: Lactose Intolerance
- Consortium to Lower Obesity in Chicago Children: Lactose Intolerance Fact Sheet
- Mayo Clinic: Lactose Intolerance
- Dr. David Fankhauser: Rennet for Making Cheese
- New Mexico State University: Making Homemade Cheese
- University of Virginia, Digestive Health Center: Lactose Content of Common Foods
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