why does my frozen breast milk smell sour

Nothing is more disheartening than tossing out breast milk, no matter how large or small the quantity. There are mothers who follow all the collection and storage guidelines, only to find that their milk, when thawed, tastes or smells bad. (They typically describe the milk as having a sour, metallic, or soapy taste. )
In the absence of other causes, it is usually assumed that lipase is the culprit. Lipase is an important enzyme found in human milk. Lipase breaks down the milk fats into small particles that babies can easily digest. Although its never been proven, its thought that high levels of lipase might explain why the milk of some mothers begins to smell bad, refrigerated or frozen. Laboratory testing is the only way to confirm the level of lipase in human milk. To avoid the added expense, some mothers simply test their milk at home by placing small amounts of expressed milk on the kitchen counter at room temperature and in the refrigerator or freezer and checking it periodically for changes in taste or smell. Fortunately, only a small number of mothers report noticeable changes in the taste of their milk as a result of storage, but if you are one of them, it can be extremely frustrating. How long the milk can be safely stored before it starts to smell varies from hours to days to weeks. Some babies refuse to drink the milk once the flavor changes. Others dont seem to mind the taste. Unfortunately, there is no way to salvage the milk once it smells or tastes bad. If the baby refuses to drink the milk, the only option is to discard the milk or donate it to the nearest. To prevent newly expressed milk from souring, mothers can heat (scald) the milk before storing it, to reduce lipase activity.


Scalding requires that the milk be heated until tiny bubbles form around the edge of the pan (approximately 180F or 82C). Do not heat to a full, rolling boil (212F or 100C). Remove the milk from the heat as soon as the bubbles appear, then cool and store. Scalding will destroy some of the milks anti-infective properties and may alter nutrient levels, but this is seldom a concern unless all of the milk a baby receives is heat-treated. Make milk storage easy and safe by storing your milk in any glass or BPA-free plastic container made for food storageincluding plastic bags specifically designed for storing human milk. Label the container with the date and time. Allow room for expansion if you plan to freeze the milk. Place a single serving in each container. More than one container can be thawed if larger amounts are needed. Small amounts of breast milk can be combined in the refrigerator to make a single serving. Human milk stored in the refrigerator or freezer should be placed in the middle of the compartment away from the door to avoid temperature changes. Do not store milk in the refrigerator or freezer door. Make sure that all packages in your refrigerator or freezer are sealed well, so that your milk cannot absorb odors from other foods. A box of baking soda placed in the refrigerator or freezer may help to absorb odors. To thaw, place the unopened container in the refrigerator or in a pan of warm water. Do not thaw or warm any milk for your baby in a microwave oven. A microwave oven destroys live cells and heats the milk unevenly, which increases the risk of burning your baby. Breast milk can be served chilled from the refrigerator or at room temperature.


No heating is necessary. If your baby prefers milk at room temperature, simply place the unopened container in a pan of warm water for several minutes. Milk that has been thawed in the refrigerator should be used within four hours once it is removed from the refrigerator or within 24 hours if it is kept in the refrigerator. Milk that has been thawed in a pan of warm water should be used right away or stored in the refrigerator for up to four hours. Fresh milk left in the feeding container should be stored in the refrigerator and used within one hour to complete the feeding. Previously frozen milk left in the feeding container should be discarded. For guidelines on how long you can store your breast milk,. Ask Anne Question : My baby is 3 months old and Im getting ready to in a few days. Ive been pumping every day for over a month to build up a freezer stash. I introduced a bottle of expressed milk when he was 6 weeks old, and hes always taken it with no problem. Heres what Im worried about: I defrosted a 6 ounce bottle today and he refused to drink it at all. I smelled it to see if something was wrong with it, and it smelled terrible. I tasted a few drops, and it tasted bad, too kind of soapy and sour. No wonder he wouldnt! I decided to check my other bottles, and discovered that they all smelled and tasted the same way. What could be causing this? Is it something in my diet? Is all my milk spoiled? Please tell me I dont have to throw away a freezer full of breast milk. I have 40 bags saved! Answer: It s probably not your diet. Breast milk is a living fluid that constantly adapts to meet a babys needs. Food from the moms diet causes subtle changes in flavor of her milk, as opposed to formula, which always tastes the same.


Research has shown that mothers diet during breastfeeding increases her babys acceptance of a wider range of flavors when he starts eating solids. Breast milk contains more lactose (milk sugar) and tastes sweeter than formula. Its been described as tasting like melted ice cream. Human milk that has truly soured has a very distinct taste and odor much like spoiled cows milk. If youre not sure if the milk is still good, just give it a sniff. If it smells spoiled, then dont give it to your baby. It wont hurt him anymore than drinking buttermilk or eating sour cream would, but he probably won t like the taste. Because of all the live cells and antibodies found in human milk, it doesnt spoil nearly as easily as formula. It will stay fresh in the fridge for a week or more, while formula will only keep for a day or two. Freezing milk changes the taste of the milk somewhat, but not significantly. Most babies will accept thawed frozen milk just a well as they do milk thats freshly pumped. However, there are some situations where frozen or refrigerated milk smells and tastes bad, even when all the have been followed. Lipase is a beneficial digestive enzyme found in all breast milk whose function is to break down fat and help digest the milk. Lipase activity increases as the milk gets cold. This means that while the baby is nursing, the milk is fine because the temperature is constantly warm. However, once it is expressed, excessive lipase activity begins immediately as soon as the milk starts getting cooler than body temperature. We dont know why some moms milk contains higher levels of lipase than others, but moms who have this issue with one baby will usually experience it with others.


The high lipase milk itself is not bad the nutritional value is unchanged, and it wont make your baby sick to drink it but it may have such a yucky sour or soapy taste that the baby fusses and refuses to take the bottle at all. The bad news is that once the excess lipase is activated, there is no way to change the taste. The only options for a freezer full of smelly milk are tossing it (nooooo!!!!!! ); mixing it with other milk or baby food to see if that disguises the taste; or donating to a milk bank. Due to the way donor milk is handled, the lipase content isnt an issue. For more information about donating milk, visit. The good news is that you can still pump and freeze your milk, even if it contains excess lipase. Heat decreases and deactivates the activity of lipase and gets rid of the soapy taste. Scald the expressed milk by bringing it close to a boil -until bubbles form around the edges- then then cool and freeze it. Freezing the milk will slow down the lipase, but scalding stops it completely. Ordinarily, breast milk should not be boiled or excessively heated, because some (but not all) of the antibodies and live cells in the milk are destroyed by heat. Human milk banks routinely heat and pasteurize donated milk, and the heated milk is still far superior to formula, which doesn t have any immune factors to begin with. Remember that excess lipase activity makes breast milk smell and taste funny, but doesnt affect the nutritional quality at all. Heat treating the milk before freezing is a real pain, but the many for your baby make it well worth the effort. Anne Smith, IBCLC

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