As raw milk consumers we often pay more for raw milk because of its higher nutrient and probiotic content. Many of us travel great distances to buy the milk and then stash some in the freezer so that we have to travel less often. Some people have even purchased frozen raw milk by mail, paying a premium for the milk itself and paying to ship a heavy and perishable item.
Should we freeze raw milk?
This is not the type of thorough review you see in the Raw Milk White Papers, but I include some research here that shows the magnitude of decline in the beneficial properties of raw milk once it is frozen.
When raw milk advocates discuss the loss of vitamins due to pasteurization, they often mention vitamin C and B vitamins. (Folks who have subscribed to the email list on this site will read more about the loss in B vitamins in pasteurized milk.)
It turns out that the vitamin C in milk may be as cold-sensitive as it is heat-sensitive. A 1983 study in the Journal of Dairy Science found that about 28% of the vitamin C in fresh raw milk is lost to freezing whereas 26% was lost to ultra high temperature pasteurization (UHT), a common pasteurization technique used with organic milk. The more conventional pasteurization process resulted in a loss of 17% of the vitamin C.
In the same study researchers found that riboflavin (vitamin B2) showed little loss in either freezing or pasteurization. However, thiamine (B1) is more sensitive to heat than to freezing.
The numbers of beneficial bacteria do decline when raw milk is frozen however the loss depends on the amount of time in the freezer.
A 1992 study in the Journal of Dairy Science on fermented ice cream found that Lactobaccillus acidophilus declined less than one log after one week frozen (from 5×10^8 fresh to 1.5 x 10^8 after one week). After seventeen weeks of storage, L. acidophilus declined by two logs (to 3 x 10^6). Bifidobacterium bifidum declines less — a decline of just over one log in seventeen weeks.
A one- or two-long decline is fairly trivial when you start with over eight logs. The actual bacteria count declined from 500 million to about 100 million in the first week. The defrosted milk will still have a good bit of bacteria, just not nearly as much as the fresh milk. Freezing certainly is far easier on bacteria than is pasteurization.
Milk has many components that may be somewhat susceptible to freezing. Antioxidant activity is one example. We do not tend to think about antioxidants in milk, but researchers are concerned about antioxidant loss in stored human milk. One study found that antioxidants are at their peak in human milk in its first two days. There is loss with both time and with freezing (Hanna et al. 2004).
While there may be other components of raw milk which may be more or less susceptible to freezing (e.g. proteins, fats), this short essay is intended to provide food for thought for raw milk consumers.
Freezing may reduce the nutritional content of raw milk on the order that does milk pasteurization. It reduces the beneficial bacteria counts as well, though not as dramatically as pasteurization.
Depending on your reason for consuming raw milk, you may want to structure your purchases so that you have a more regular source of fresh raw milk. You may consider culturing some of the milk you purchase as a preservation technique rather than freezing it. You may also consider culturing a pasteurized dairy product when fresh milk is not available.