Is it my imagination or does skim milk go sour more quickly than whole milk?

Not that I have ever noticed.

This is a recognized phenomenon, yes. It’s not because bacteria grow faster in skim milk, though; in experiments under controlled conditions, the growth rate is the same for both. The difference is in the flavors that result from the bacterial growth.

Bacteria release enzymes that break down various components of the milk. One of these is protease, which targets the milk proteins. The by-products of this enzymatic reaction are particularly bitter tasting. After a given period of bacterial growth in the two kinds of milk, the number of germs will be about the same, but the skim milk will have considerably higher levels of protease and proteolysis byproducts, so it will tend to taste nastier. The speculation is that the fat globules in whole milk inhibit the access of the protease to the casein proteins. Whole milk develops spoilage flavors that tend more toward sourness than bitterness, and these are less likely to be interpreted as alarming.

^^^Yet another item to add to my ever-growing list of alarums?

Just discovered in fridge one half-used jar of food coop marinara sauce and and one half-eaten container of hummus that have grown green sweaters, speaking of alarming.

Well..I wouldn’t be too sure about skimmed milk, but the trick with semi-skimmed? Freeze it. That’s right. Stick it in the freezer, I kid you not. A good pint of milk will last for quite some time stuffed in a freezer. I wouldn’t recommend doing that with full fat milk though – skimmed milk…maybe. May not have answered the question all that well, but did you know you could do that?

@lightsourcetrickster No,I didn’t know that. I assume you have to thaw the amount you froze before using it? So you put it in 1 cup zip locked bag? I’ll try it.