Sour Frozen Breastmilk and the Great Formula Switch

It was three months in the making. Kathleen’s five-day business trip to San Diego meant that I would be left with TD, and we planned for the occasion accordingly. The biggest preparation was Kathleen’s weeks-long pumping escapade. She pumped and pumped and pumped until we had over a gallon and a half of milk to feed to TD while she was away. Since we were diverting almost all of the pumped milk to the freezer it meant I couldn’t lend a hand during the overnight feedings. Kathleen shouldered the burden in order to leave TD behind and keep the goal of an all-breastmilk diet¹. It was a worthy effort. Bags of frozen cubes of milk took over our freezer, and after we hit our milk quota, Kathleen managed to add a 20 percent surplus.

On day one of Kathleen’s trip, I pulled out the day’s allotment of milk to defrost. I proffered TD the bottle and she gulped and gasped and screamed and gurgled. In general, as long as the milk is not ice cold TD is not particularly fussy about milk temperature, so it was strange when she struggle to drink the milk during the day. She was eating a less and less, and by the mid-afternoon she was crying inconsolably. Nonie² had come to help out while Kathleen was away and noted a solid hour of crying. She wouldn’t eat. She couldn’t sleep. TD was apoplectic.

This had never happened before. On the Fussy Baby Scale, TD lands way on the “easy” side of the spectrum. She cries for a reason, so there must have been a reason she was losing her mind, and diagnosing this particular problem proved challenging. Finally, after several failed attempts, TD choked down a 5oz bottle of breastmilk in desperate, but reluctant, gulps and went to sleep. I went through the scenarios that occurred to me:

• Was it the new bottles we had purchased? Probably not. While they’re larger capacity, they’re the same nipple and construction as the bottles TD has been drinking out of for weeks.
• Was it the temperature? Initially, I thought it was too cold, but even bringing the milk up to room temperature didn’t seem to help.
• Was the milk bad? The smell was a bit strange, yes, but I attributed it to new bottles having some sort of factory scent I failed to successfully wash out. I didn’t consider it possible the milk had spoiled because it went directly from the pumping session into the freezer

Finally at 2:30am, TD blew up into a nighttime fit I had never seen. She was desperately hungry, sucking and rooting and screaming intermittently. I grabbed milk in one of the new bottles and she rejected it outright. I switched to an older bottle that I knew she liked and she screamed even louder. Finally, I decided to taste the milk for myself and I gagged. What the hell? Sour milk?

I ran to the freezer and defrosted cubes from a different bag and tasted them. Gag again. I had eight bags of frozen milk cubes, were any of them any good? With a shrieking baby upstairs and a 2:30am level of brain function, I made a quick judgment call: I pulled 4oz of formula from the samples we received at the hospital; TD sucked it down in less than three minutes and went back to sleep.

In the morning, while TD was still snoozing, I tested cubes from all eight bags of milk. Every single bag of milk had soured. It was Thursday morning and Kathleen was in San Diego until Sunday. I didn’t know why the milk was bad, but I couldn’t subject TD to 5 days of gross milk. I had no choice but to run out to the store and pick up a canister of formula.

I was perplexed and disappointed. Perplexed because I had no idea how it was possible how 180 oz of immediately-frozen breastmilk could spoil, and disappointed because Kathleen had worked so hard to build up a five-day store of milk. The sacrifices she made in the first six weeks of TD’s life were real and frustrating, and they were all for naught³. I literally watched the result of Kathleen’s work go down the drain.

So what the hell happened? Turns out frozen milk turning sour is not unheard of. Evidently, some women produce milk with an excessive amount of lipase, the enzyme that breaks down milk fat. The activity of the enzyme is accelerated when the milk gets cold, and goes into light speed when frozen. For most women, this doesn’t pose a problem. The frozen milk’s flavor doesn’t get changed much. But for women like Kathleen, the extra lipase essentially turns the frozen breastmilk cubes into buttermilk. There isn’t anything dangerous about it, but it is very gross, and I can tell you from experience that babies do not like the flavor. At all.

Some solutions call for scalding the milk⁴ before freezing. This poses two fundamental problems: it’s a pain in the ass to do this every time you want to freeze milk, but more importantly, scalding the milk actually kills some of the good bacteria/nutritional hoo-ha that’s in the milk, this is why people are warned against microwaving the milk.

This brings up a valid issue: it’s important to have a taste of fresh breastmilk for yourself so you know what it’s supposed to taste like. This baseline is a critical touchpoint for comparison when something goes sideways with feeding. I’m sure gagging on the sour milk would have tipped me off that the milk itself might have been an issue, but then again had I not tasted it weeks before, I might have thought, “Well, maybe breastmilk is just gross? I wouldn’t know.”

It’s disappointing that Kathleen’s breastmilk is so fragile, but in the grand scheme of things switching TD over to Similac for a week or so every once in a while isn’t that big of a deal⁵. I believe that we can get TD back on breastmilk by the end of the week. If we can’t, I’m not that worried. Formula babies are people, too.

1. This meant I got to sleep through most of these feedings. My guilt at getting full nights of sleep in the first six weeks may have been offset by Kathleen’s guilt of leaving her family for five days, so you know, life’s a balance.
2. My mother.
3. Kathleen feels very strongly about breastmilk. While I am more moderate in my view (I certainly don’t have anything against breastmilk), I’m happy to support Kathleen’s desire to feed TD breastmilk exclusively.
4. Bringing the milk up to 180F in a saucepan.
5. If you listen to the legion of crazed breastmilk advocates, you’d think that formula sucks the soul out of babies and turns them into evil creatures of the night, which I mean, come on, really?