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  • Writer's pictureMegan Dunn


Updated: Jan 2


So, there could be a few reasons behind changes in the smell or taste of breast milk. The first thing to do is figure out if the way you're pumping, handling, or storing the milk is the issue, or if it's because of something like strong lipase activity or chemical changes. That's the first step to finding the right solution. So, let's talk about how pumping. It's really important to make sure you're being careful with hygiene. How clean your hands and pump parts are affects how long milk can be stored. After each time you pump, you need to clean all the parts really well. I know some people do "the refrigerator hack" but I don't recommend it. It's better to get extra parts so you can clean in batches if cleaning each time is challenging. Cleaning each time you use the pump and sterilizing daily, makes sure there's no bacteria or yeast hanging around to get into the milk. The Centers for Disease Control and Prevention (CDC) have step-by-step cleaning guides in both English and Spanish When it comes to storing breast milk, only use containers made for this purpose. Lawrence and Lawrence suggest going for hard plastic containers made from something called polypropylene. This helps keep more of the good stuff in the milk, like nutrients and immune factors, compared to other types of containers.

If you can't find those polypropylene containers, Pyrex glass containers are the next best option. They're not perfect, but they're better than some other choices. Other types of plastic bags for breast milk are not the best choice. They can mess with the milk's components and can even break sometimes, so they're kind of a backup option. Let's talk Lipase We used to think that some people had too much lipase in their milk, but new research says that's not quite true (Lawrence and Lawrence, page 137).

Lipase is this enzyme found in all kinds of milk. There are two types: lipoprotein lipase and bile salt-dependent lipase (you can dig deeper in Lawrence and Lawrence, 2016, pages 136-137). These enzymes are helpful for digestion and giving the baby some immune benefits. So, it's not a bad thing at all! Lipase activity:

  • supports an infant’s ability to digest fats (lipids; Lönnerdal and Atkinson, 1995, p. 361) by ensuring that the fat molecules remain well-mixed into the milk in a small, easily digestible form (Lawrence and Lawrence, pp. 136-137)

  • breaks down triglycerides to release fat-soluble nutrients (Lawrence and Lawrence, p. 137)

  • releases free fatty acids that provide immunological effects (antibacterial, antiviral, and antiprotozoan; Lawrence and Lawrence, p. 136)

  • protects against infection by intestinal parasites such as Giardia and Cryptosporidium (Lawrence & Lawrence, p. 463)

Now, let's dive into something called "high lipase activity." Basically, when there's too much of this lipase doing its job on the fats in your pumped milk, it can make the milk smell like soap or fish, and sometimes even taste that way. But guess what? Your baby probably won't care.

How fast this happens depends on your milk. Some folks notice the change in less than 12 hours, while others might not see much difference for a few days. Even if your milk smells a bit like soap, don't worry, it's still totally safe and good for your baby. But if your baby's giving you the "nope" face, you can try mixing the soapy milk half and half with freshly pumped milk. That usually does the trick.

To avoid this happening in the future, just freeze your milk right away. That can help keep the soap smell at bay. Chemical Oxidation

Alright, let's talk about something trickier: "chemical oxidation." If your milk smells sour or rancid, it's likely because of chemical oxidation, not too much lipase action (you can explore more in Mohrbacher, page 461).

This one's a bit complex. There could be a bunch of things causing it. Like, if your diet has a lot of saturated fats or even drinking water with stuff like copper or iron, that can be part of the problem. The thing is, once this chemical change has happened, the milk can't be fixed.

Possible solutions include:

  • avoiding fish-oil or flax-seed supplements, anchovies, old vegetable oils (a smell or taste test can help you determine whether an oil has gone rancid), some nuts (Brazil nuts are especially likely to become rancid) or other foods that may contain rancid fats (Mohrbacher, p. 461; Vieira, McClements, and Decker, 2015, p. 313S – 315S).

  • drinking bottled water or water from a different source than usual to reduce the potential for iron or copper ions being a cause (Mohrbacher, p. 461).

  • increasing one’s antioxidant intake may help prevent this problem, so you might try including beta carotene and vitamin E in your diet (Mohrbacher, p. 461) to see whether it helps.

When chemical oxidation occurs, the milk is spoiled and must be discarded, and scalding the milk will only make the problem worse. However, the above dietary changes should help you resolve the problem completely without the extra work of heat-treating your milk! HOW CAN YOU FIND OUT WHICH PROBLEM—HIGH LIPASE ACTIVITY OR CHEMICAL OXIDATION—YOU HAVE?

So, let's do a little detective work to see what's up with your milk. Once you've confirmed that your pumping gear is squeaky clean, pump or express some milk and give it a good sniff and taste. Is it sour-smelling or does it seem alright with a touch of sweetness? If it's got that sour vibe, it's a sign of rancid fats and chemical changes. To tackle this, think about changing up your diet to sort things out.

If it's smelling good and has a little sweet taste, pop it into the fridge. Over the next few hours, give it another smell and taste test. (By the way, you can safely keep milk in the fridge at around 39ºF/4ºC for up to 8 days, though sooner is better – more details in Mohrbacher, page 461). You can also freeze a small batcher and then after about a week, check the smell and taste again. Most folks find that their milk stays just fine.

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