Why does milk sour faster in a smaller container?

I take a 16-oz container of milk to work for tea. I can use it for three days, tops, but by the end of the third day, it’s starting to smell “off”, and on the fourth day, it will curdle when poured into the tea. Meanwhile, the gallon jug of milk at home, from where I got it, will not show any signs of spoilage, right up to, and sometimes past, its expiry date.

Does anyone have an idea why it works like this?

A smaller ammount of milk has a larger surface area relative to its volume, thus exposing more of the liquid to the air.

I am guessing that the smaller container spends more time outside of the fridge. I know mine stays on my desk until I get around to walking back to the kitchenette at work. At home, the gallon comes out to be poured, then goes right back into the fridge. Also, a smaller amount of liquid will change temperature faster than a large one. Finally, could the fridge at work be a little warmer than the one at home?

Get some ultra-pasturized mini-moos.

Even if it doesn’t spend more time outside, it will heat faster, having more surface area.

In office fridge, you’re probably looking at a lot more door-openings, and therefore temperature fluctuations, than in a home fridge. Therefore, I’d bet that the milk is not being kept quite as cold as at home, which allows it to spoil faster.

Also, although I don’t know if my experience being with my local Norwegian grocery store makes it invalid, have you checked the expiration dates? In my experience large containers, being what people buy the most of, are in and out of the store on the same day, or close, and are likely to have close to the maximum of “useful days” left. Smaller containers on the other hand, might stay on the shop shelf for several days, and get sold much closer to their expiration dates, merely because of lower turnover.

Bolding is mine.

I’m guessing the smaller container you’re pouring the fresh milk into might not be quite as clean as the gallon bottle that was filled at the dairy.

I think we need an experiment to establish whether the container size is really the problem. Pour some milk into a pint container as identical as possible to the one you take to work, and leave it in the fridge at home. If the pint at home sours faster than the gallon it came from, then container size is the problem. If not, then the problem is the temperature in the work refrigerator, or the greater amount of handling the small container gets, or perhaps the more-pungent bacterial flora at work (and when was the fridge at work cleaned last?).

And also one to see if the cleanliness of the container is the cause. Instead of pouring some milk from a gallon bottle into a pint container. Buy a gallon and buy a pint with the same expiration dates, open them both, pour a little out of each, then leave them both in the same fridge.

I suspect that there is a minute amount of bacteria left in the container when you clean it. The sterilized gallon container doesn’t have this starter culture.

I use milk slowly, on the morning oatmeal only. I buy a half gallon for economy reasons and it lasts about 2 weeks. I find, contrarywise, that it keeps longer when I pour it into a quart container at the end of the first week. I think the empty surfaces in the half empty container allow bacteria to grow and mix with the milk left when I pour it.

I buy 4 pints at a time because it’s on permanent offer at £1.00. (2 pints is 87p). My wife can’t handle the 4 pint container so I transfer it into a 2 pint one - I have been using the same one now for at least six months. We use about 8 pints in three weeks so some weeks I don’t buy any.

We have been away for a few days so I am now using milk that’s been in my fridge at 4° C for two weeks and it will last me at least another week. All I do is scald the smaller container before transfer.

So far, I have not had any problems with the large or the small containers.

What kind of container are we talking about for the 16 oz.: plastic? Clear or cloudy? Glass?

How big is the opening? How do you clean it before you refill it?

Glass is much more hygenic than cheap plastics. A recent study found that a lof plastic that food is sold in meets the standard of safety only for one-time use, not if you wash and re-use it. Apart from particles the plastic might emit, plastic easily gets scratched, and bacteria can take hold there. The structural integrity of one-way plastic can easily be comprosmised with too-hot water when washing up, so substances get emitted into the milk you fill into it, which is not good for you.

I find containers with large openings easier to clean, but not always available when buying.

With clear glass (or clear plastic) you can if there’s a film of bacteria; but with coloured glass or cloudy plastic, you can not see. If a film already exists, it will spoil any new milk much faster.

I have the same problem with my Nespresso machine’s milk container. It’s plastic, and it’s made to be removed from the machine and put in the refrigerator so you can use it again later. I make one cappuccino per day, and if I leave the milk in that plastic container for more than two days, the milk goes bad. I now weigh the container and put exactly two cups worth of milk in it, and after two uses I wash it out, and let it dry before filling it up with two cups worth the next time I want to use it.

NO its not due to contamination.

The reason pasteurized , but not ultra pasteurized , milk goes sour is that there is still a bacterium surviving being pasteurized . The reason its not all ultra pasteurized is that is high enough temperature*time , to kill the bacterium AND so high enough to burn the milk and make it taste a bit different.

So that dispells the idea that contamination is required for the milk to go off.

Off means the specific bacterium, passed on from cow to cow, has produced enough acid to curdle the milk.

Now… the contamination you will get from opening the milk is not going to be the same.
its going to be mold spores mostly, or yeast, and you’d know if it was growing a contamination! Its going to be totally different to simply “off” due to the lactic acid.

That would be true only if the milk remained in the pasteurized state. But once you open it, the air it comes into contact with introduces new bacteria.

Actually milk can go “off” = non-drinkable in different ways. If you have fresh milk and just let it stand, you will get “thick” milk, which people used to eat as dessert.

If you have pasteurized, but not homogenized*, milk, the fat will still collect and it will go “off” differently than pasteurized and homogenized milk, which will go “bad”.

There’s also a new procedure on the market since a few years, Ultra- High Pasteurization, usually called Extended shelf life. It still needs a fridge, but instead of lasting up to 10 days, ESL milk lasts for almost a month.

Also, pasteurized milk is stable milk you can keep at normal temperature (until you open it) for 2 months (and needs a fridge only after you open it), while normal milk needs a fridge all the time to last for a week.

*homogenized means that the fat in the milk is broken into tiny particles. It stops the cream from forming at the top. Some organic milk is sold without (I like the cream) and it doesn’t go bad, just sour.

Do you want to know about the container they used in 2005, or the one they use now? :wink: