I just don’t get it. I’m sure there’s a very sciency explanation, but it makes no sense to me. I love that it can sit out to be soft and spreadable, but you try that with cream and you’re on the way to a stinky cheese, milk or yogurt you’ve just got a curdled surprise.
So why can butter just sit out and not start to stink or become dangerous to eat?
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Butter actually does become rancid, it just takes much longer because it’s mainly fat and bacteria doesn’t grow as well in fat as it does in water. Milk etc. has more water than butter does.
Butter *can* turn rancid though….made the mistake of leaving it out during a very hot week with no A/C.
I have had butter go bad when left on the counter during a hot summer. I have even seen refrigerated butter go rancid (it was at my SILs house) my partner and I said no thank you to buttering our toasts.
A quarter pound stick will only have about 24 hours or so to decompose until it is consumed where I’m at, so that problem never arises this time of year. There are some spring, and summer, and fall days that will turn a stick of left out butter into a yellow pool of goop though.
The “sciency explanation” is just “bacteria need water to live and grow in”.
Milk/cream/yogurt contain lots of water, so the spoily bacteria can live in them. Butter is almost entirely fats/oils and much less water, so bacteria can’t live on it.
I feel there is a true ELIF missing.
Here’s my try. Food doesn’t go bad by itself. If you threw a hot dog into space it would be fine to eat for a very very long time. What happens is little creatures, like bacteria and fungi start eating some components of the food. Most of them need also water and oxygen to live, but some don’t. Also, some parts of the food can go bad from contact with oxygen (oxidation) sunlight (UV) or degrade with changes in temperature. Butter is made by removing most of the water, and the remainder is in very small separated droplets so microorganisms can’t damage it easily.
However oxygen and light do degrade the fats in the butter, creating a rancid flavor. So even if its safe to eat, the taste will grow worse after a few days without refrigeration.
The reason is much more simple than most of these comments are positing. The butter has no water in it and doesn’t not absorb water from the air. This concept is why dried foods, honey, pickled, and powered items are shelf stable. Some of them will eventually pull water from the air and start rotting but if they are sealed they are basically good forever. Things will still oxidize though which is what causes things to go rancid. If you remove both water and oxygen you end up with nitrogen sealed freeze dried items which will last for as long as the seal holds and they are kept at a reasonable temperature.
Every answer here is different… Oil/fat content, salt, different *types* of fat, oxidation speed…
Either redditors are just going off of gut feelings and need to cite more sources, or butter just has multiple qualities that facilitate a long shelf life.
Either way, redditors need to cite more sources.
Pure fat, pure sugar, pure vinegar, and pure salt are amazing preservatives. This is why we have salted dried fish, jerky, pickles, jam, and confit available on the shelves. Admittedly, fat preserved items are less popular these days, in part because they’re a bit harder to reliably preserve. Also because the Western world would find it kind of gross. Sardines are a common example.
Butter is sufficiently high fat to be reasonably well preserved. Add salt to the butter and it will be even better preserved. Reduce the water content for even longer preservation. Ghee, which is butter with the milk sugars, proteins, and water removed, is almost 100% fat, and is shelf stable for months.
Butter is about 80% fat, a few % milk solids, and the rest is water. Fat/Oil is not an ideal growth medium for bacteria. All the other things you listed have much more water and sugars(lactose). That is Great medium for bacteria growth.
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