When my sister became a doctor, all of our friends and family began asking her questions and for advice for their aches and pains. I never though that something similar would happen when I became a cheesemonger. No, people didn’t come to me with complaints of their aches and pains, but my sister-in-law’s brother asked me if there was any lactose-free cheese and which ones they were. Curious, I did some investigating…
Lactose is a type of sugar found in milk and other dairy products. Human babies are born with the enzyme lactase, which “breaks down” lactose by cleaving it into the two monosaccharides glucose and galactose for easier digestion. When the small intestine does not make enough of the enzyme lactase, is not able to digest lactose and lactase deficiency, or lactose intolerance, occurs.
Lactose consists of the two simple sugars, glucose and galactose, bonded together. The molecular structures of glucose and galactose are carbon rings surrounded by hydroxyl (-OH) groups and these hydroxyl groups are polar, which means that each group has separate regions of positive and negative charge. The fact that the -OH group is polar in nature enables lactose to mix well with the polar molecule water. Since whey is mostly water, when the whey is drained from the curds, most of the lactose that hasn’t been cleaved already is removed from the cheese when the whey is.
As outlined by Professor Frank V. Kosikowski, adding starter culture to milk is the first step in the eight steps of cheesemaking. The starter culture initiates, or starts, the production of lactic acid through its fermentation of lactose — hence the name /starter/. Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a sugar, into an alcohol or an acid. Use of a starter culture provides a uniform, predictable, reproducible rate of acid production during cheese making.
Once the lactose is cleaved into it’s simple sugar components, the glucose molecule is metabolised and undergoes glycolysis to produce pyruvate molecules. Pyruvate, or Pyruvic acid, supplies energy to living cells through the Krebs cycle (metabolic cycle for aerobic organisms) for the starter bacteria and alternatively ferments to produce lactic acid when oxygen is lacking.
While it is true that a small amount of lactose is carried over into the cheese, it is very important because it serves as an energy source for bacteria present in the cheese. Although fresh cheeses typically contain some residual lactose that may be problematic to lactose-intolerant individuals, aged cheeses generally do not present a problem because the residual lactose is fermented to negligible levels during ripening/ aging.
So, the bottom line is that most of the lactose is either lost to the whey or fermented by the starter culture during cheesemaking.
P.F. Fox states that there is no lactose in many cheeses or only a very low concentration (1-3 g/ 100g) because most of the lactose of the milk passes into the whey and that retained in the cheese curd is partly or fully converted to lactic acid during cheese ripening.
Lactose Intolerance. MedlinePlus: A Service of the U.S. National Library of Medicine – National Institutes of Health. Oct 23, 2012
Paul Kindsedt. American Farmstead Cheese: The Complete Guide To Making and Selling Artisan Cheeses. Chelsea Green Publishing, 2005.
P.F. Fox. Cheese: Chemistry, Physics and Microbiology: Volume 1: General Aspects. New York: Chapman & Hall, 1993.