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The amount of lactose in cottage cheese can vary considerably depending on the process used to make it. Though there is always some lactose in cottage cheese, when it is made with fermented milk products, it does not contain much and is usually well-tolerated by people who have trouble digesting lactose. The fermentation process allows bacteria in the cheese to break down lactose and transform it into lactic acid. Cottage cheese that is soured through other processes may have a considerable amount of lactose in it.
When it is made in the traditional way, cottage cheese contains only a small amount of lactose. In the traditional process, buttermilk, which is a fermented milk product, is used as the basis for the cheese. In order to make buttermilk, a bacterial starter is added to milk and then the milk is left at room temperature for between 15 and 24 hours. During this time, bacteria in the milk, such as acidophilus or bifidus, feed on the lactose and secrete lactic acid as a byproduct. Though these bacteria do not consume all of the lactose in the buttermilk, they are able to eat most of it in this amount of time.
After the milk has had time to ferment, it can be used to make cottage cheese. The curdled milk is cooked slightly until the curds have hardened and separated from the whey. At that point, the whey is drained and the cottage cheese is allowed to cool. The amount of lactose in cottage cheese such as this will not usually be enough to bother people who are lactose intolerant.
Large curd cottage cheese may have significantly more lactose in it than small curd cottage cheese. This is because the cheese is made quickly and is curdled in part through the use of rennin. The milk is fermented for less than an hour, giving the bacteria very little time to transform lactose into lactic acid. The amount of lactose in cottage cheese made in this way is usually similar to the amount found in fresh milk.
It is possible to buy dairy products, including cottage cheese, that have been treated so that they are completely free of lactose. Lactase, the enzyme used to digest lactose, is added to these products to pre-digest the lactose before a person eats it. By carefully controlling this process, manufacturers of lactose free products are able to ensure that there is no lactose in cottage cheese at all.