Dec 23

Testing Stinky Breastmilk for Lipase Breakdown … Biochemist style

I went back to work last week.  I had a great time doing science after three months of 24/7 mommydom.  Don’t get me wrong, I love being a mommy.  I simply also loooove science.  Anyway, Izzy was charged with giving Teagan (our little boob monster) bottles of my breast milk while I was at work.  Teagan had been taking a bottle (somewhat) after 6 weeks of trying.  But, when he went to give her the first bottle when I was at work she refused it again.  She refused it all week!  Luckily, I am only back at work part time so she didn’t go too long without eating.  That Friday, Izzy decided to smell the milk he was giving her and discovered that it didn’t smell very good.  No wonder she was refusing it!  It was super stanky!

For two months, I have been pumping in the morning and freezing milk to later be used.  We in the parenting world call it a stash.  I had one awesome stash going.  Discovering that it smelled stanky when thawed was heartbreaking.  I immediately started googling.  A few things could be going on.  First, my milk may naturally contain either high levels of the enzyme lipase (frakking enzymes, they torture me!) or my lipase may be overactive.  Lipase breaks down fats and is believed to contribute to early stankiness in breast milk.  The milk isn’t bad but it smells and tastes bad and our picky little boob lover doesn’t want anything to do with it.  Second, something about the way I was freezing it could have been altering the smell/taste.

I decided to test the lipase issue first.  Scalding the milk inactivates the lipase enzyme.  However, scalding may also have other unwanted effects such as inactivating all those wonderful little antibodies (both are proteins).  We might be able to get away with doing a quick thaw in hot water instead of a slow thaw overnight.  This will give the lipase enzyme less time to turn my milk stanky.

So, I set up the following experiment (my degree came in handy, woot):

My BM (breast milk) is stanky and funky tasting when I thaw it. This makes Teagan MAD!

Hypothesis 1:
My BM has excessively high lipase activity.  Scalding it will fix the problem.

Hypothesis 2:
My BM has excessively high lipase activity. Thawing my BM in the fridge over night results in the stankiness and quick thawing will fix the problem.

Experimental methods:
Pump 5 ounces of BM while at work. Bring home in cooler. After dinner, take 2 ounces and scald. Divide scalded BM into two Medela bottles. Pour 1 ounce unscalded BM into two more Medela bottles. Freeze all four of these bottles. Refrigerate final ounce.
Next evening, take one of the unscalded and one of the scalded bottles and thaw in refrigerator over night.
Following morning, remove the two remaining frozen bottles and quick thaw in heated water. Put back in the refrigerator.
That evening, perform stank-detection test.
Stank detection test:
step 1- smell and taste each bottle
step 2- ask Izzy to smell and taste each bottle

Update : Proper Scalding Technique
I have discovered that studies on cow lipase have shown that it denatures at 70° C (160° F). Cow lipase is highly likely to be similar or identical to human lipase, so the safe thing to do is to heat the milk to 165° F. I use a candy thermometer for this.

Step 1 and 2 yielded identical results.
Fresh (unfrozen) BM was extremely stanky.
Unscalded BM, both slow and quick thawed, was slightly stanky.
Scalded BM, both slow and quick thawed, was not stanky.

Scalding my BM solves the stank problem!!! Unfortunately, this means I have to chuck my entire stash, as it is stanky. It is possible that we can quick thaw it and immediately give it to Teagan but we cannot thaw it and then send it with her to daycare. But at least I know that I can bring my BM home, scald it, and it will be fine when I go to thaw it fast or slow.

Future work:
Test my stash. Pump more milk, scald it, and rebuild my monster stash!


I’m so glad we solved the problem.  I’m not happy that I have to add the step of scalding my milk and that scalding will reduce the immunological boost that makes breast milk so awesome.  However, I still believe that breast milk (even scalded) is superior to formula and I will only give my munchkin the very best.  She is still getting it straight from the source for all but two feedings per day.  So, she’s getting plenty of the good stuff.


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  1. Jen

    I am concerned about this as I too am breastfeeding and would like to start building a stash for when I return to work. I am wondering if there is any length of time I should leave the milk frozen before removing it to do a “stank detection” test, any idea?

  2. erin

    If it truly is the lipase enzyme that is the problem, then the answer is … it depends. Enzymes (in general) work much more slowly at low temperatures. The easiest thing to do would be to put an ounce or two in the refrigerator and monitor the smell and taste over a period of about a week. Most women’s milk will not get stanky until somewhere between day 5- day 9. Mine gets stanky overnight. If yours still smells and tastes fine after 5-7 days, I’d say you’re probably in the clear. Good luck!

  3. Maeve

    My milk goes sour within 10 minutes!!! I tried scalding it right away and it got stinky within 20 minutes still! Ugh, so frustrating. Perhaps I am not scalding correctly? Thanks for the info by the way! I see this is an old post, I hope you made it through this stage with your sanity!

  4. erin

    I usually took the milk up to 164 degrees F or so, you shouldn’t really go above 170. Lipase breaks down at around 160 degrees or so, so that should work. How long are you keeping it at 165 degrees? I just let it get up to 165, then immediately cooled it in an ice bath, you may want to try that as well.

  5. anniebio

    Just a note for others going through this experience… you can donate the milk! It’s still perfectly nutritious and will go to NICU babies who benefit very much from human milk. Just search for “milk bank”. You need to go through a medical screening process first, but the effort is worth it for how many babies benefit from a few hundred ounces of milk.

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