Stale Milk: Causes And Solutions
Stale milk can be a major problem. During breastfeeding, it is common practice to express and freeze breast milk. However, while frozen, breast milk can develop a rancid taste. This event induces stress in the infant feeding routine and increases mothers’ concerns about the quality of their frozen breast milk.
What is the recommendation for freezing breast milk?
Recommendations for storing expressed breast milk vary depending on storage conditions. In general, breast milk storage can be done at room temperature, below 26 degrees Celsius, for 4–6 hours.
Also, it can be stored in a refrigerator at temperatures below 4 degrees Celsius for 3–8 days. Finally, in a freezer at temperatures of −17 to −20 degrees it can be stored for at least 3 months. Consequently, when breast milk is expected to be consumed after 3 to 8 days, freezing is a common practice for mothers handling their milk at home.
What Causes Stale Milk?
The typical taste of rancid milk is caused by the lipolysis (or digestion) products of the milk. At this point, it is important to note that, at the time of birth, the baby’s gastrointestinal system has not reached maturity.
Thus, many of the digestive functions are incipient or absent in the newborn. Only by twelve months will all of the gastrointestinal functions have been acquired.
But wise nature has it all arranged. Breast milk, in addition to its high fat or lipid content, also has the enzymes necessary for its digestion: lipases. When lipases attack the lipids in milk, it turns rancid.
The details of this process
The digestion of triglycerides (TG) in milk causes the release of glycerol and free fatty acids (FFA). As large amounts of FFA accumulate, the rancid taste of milk increases. This is mainly due to volatile short and intermediate chain fatty acids.
In fresh milk, milk lipids exist as globules of fat 0.1 to 20 microns in diameter. Such globules act as bags that enclose the triglyceride content and their membrane isolates the internal TG from the lipase that travels in the whey. For this reason, fresh milk is never stale.
However, the freezing process results in the crystallization of milk lipids and damages the membrane of the fat globule. This is what allows milk lipolysis to occur.
Lipases from human breast milk
Human milk differs from cow’s milk in that it contains two lipases: lipoprotein lipase and bile salt-stimulated lipase. The presence of lipases in ingested milk has important nutritional implications.
Thus, thanks to the fact that lipase breaks down TG, the baby’s body can assimilate this fat. Therefore, the function of lipase is prodigious and very useful for the baby.
But why doesn’t all milk go rancid?
It is important to understand that lipase content varies from mother to mother. In fact, some women express more lipases or possess lipases that are more easily activated. For that reason, not all mothers have stale milk problems.
Will stale milk hurt the baby?
This is the most frequent doubt in women whose milk turns rancid due to freezing. Stale milk is definitely not bad for your baby. This milk is not contaminated, nor will it cause any illness in the infant.
It is appropriate to consider that babies already know the taste of predigested milk. Every time you have regurgitation, milk from your stomach that has already undergone the action of lipases reaches your mouth. Despite this fact, it may happen that the baby resists the taste of stale milk and, consequently, rejects it.
What to do if the baby does not tolerate stale milk?
When babies refuse thawed milk, experts who have studied this issue recommend trying to provide freshly expressed breast milk or frozen breast milk for less than 7 days.
At the same time, it is important to put into practice the precept of using the oldest milk first in the refrigerator or freezer. Always remembering that the freezing time limit is less than 7 days. All this in order to avoid the stress of infant feeding.
Finally, it is also known that pasteurizing (or blanching) fresh milk before being frozen inactivates lipases, reducing rancidity.
