If you leave a glass of milk out on your kitchen counter for a week, it’ll turn nasty.
If you leave a stick of butter in your butter dish on the kitchen counter – you’ve still got perfectly good butter (assuming it doesn’t melt).
Why is that?
There’s not enough water in it for most bacteria. It can go rancid, but that’s an oxidative process that takes a while.
What about various brands of margarine?
My wife and child have the habit of leaving margarine and/or butter on the counter when we are eating dinner - after serving and before cleanup. Some brands (such as Parkay) find this intolerable and are nearly soup when the meal is over and it’s time to put them away. Others, like “I Can’t Believe it’s not butter” aren’t really affected and remain about the same consistency.
Are they safe to leave out? Why do they “perform” differently when left unrefrigerated?
Butter does have milk solids so it will spoil eventually (go sour) but as noted it is probably will go rancid first. Rancidity is a transformation of the fat molecules that makes it bitter and nasty. However, clarified butter (known in India as ghee) has the milk solids removed, is liquid at room temperature, and can keep for quite a while. I don’t know what keeps it from getting rancid.
They’re safe to leave out though may become unpalatable, as described above for butter. Margarine is mostly hydrogenated soybean oil. The hydrogenation makes it solid at room temperature (or just below). I suppose different brands use different processes for this. Generally the more saturated a fat is, the more solid it is at room temperature and hydrogenation causes it to be more saturated. I am not familiar with the ingredients/processes of the brands you mentioned and I am not a food chemist, so I don’t have more to offer.
OK, sounds good, thanks. But this then leads to the follow-up question – why does cheese get moldy?
This has come up before. Unsalted butter will get nasty fairly quickly if not refrigerated. Salted butter will stay fine at room temperature for a pretty long time. The salt dissolves in the water phase and won’t let anything nasty grow. The oil will eventually oxidize, making the butter taste bad.
Margarine is just vegetable oil that has had hydrogen passed through it to make it solid at room temperature. Take a bottle of your cooking oil out of the cupboard and look at it. That is what you are spreading on things when you use margarine. Yes margarine is safe to leave out, the texture may suffer but it will take a long time to spoil. It will eventually go rancid like any other oil.
Butter comes in salted and unsalted. The unsalted will go rancid faster than salted because the salt helps preserve the butter by lowering water activity. The only two ingredients listed on the butter in my fridge are pasturized cream (milk) and salt.
Cheeze is another dairy product with high levels of added salt, for the same reasons.
Cheese usually turns moldy initially from handling.
Cheeze gets moldy after it has absorbed enough moisture from the air to raise the water activity at the surface of the cheeze and allow the growth of mold.
I thought we were talking about the stuff made from milk, not the imitation products.
Rancid fats not only taste bad, but they are bad for you. They could increase your chances of cancer and heart disease.