Why skim milk not curdle
I make a low fat version of a cream soup (yes, I realize some people will say just have a small amount of the real thing- but I personally rather have a larger amount). Anyway, the recipe calls for skim milk. I thought the reason people use evaporated milk was because skim milk curdles? Skim milk obviously makes the lowest cal option and therefore is appealing to me. As a side note, I make oatmeal in the morning with milk and fruit (acid) and it doesn't curdle.
Of the low fat cream alternatives (half-and half, evaporated milk, or 2% and skim) which have you all had the most success with?
Skim milk will certainly curdle. I do it all the time to make sour milk for making muffins. Evap milk is really only milk that's been processed to remove half the water, that's all. I have had no trouble using skim milk to replace any of the higher fat milks and creams, unless it's richness depends on the higher fat. There are other ways to make a soup a little creamier without adding fat. Lightly thickening it with a little potato, using potato flakes is a quick way. Personally, I'm quite comfortable with using the skim milk without the extra fat.
Evap gives the illusion of extra creaminess. I use powdered, reconstituted, for baking and cooking, so if I want it thicker, a la evap, I just use more of the powder. By the way, I taste no difference. Nor do fussy friends and family. It's all in how it's prepared.
Milk doesn't always curdle in oatmeal with fruit for me, either. Maybe it needs more acid than other milks. I don't know. In what way are you asking about using it as a replacement?
I make cream soups that are not thickened, using the skim milk instead of cream or evap all the time.
Skim milk will curdle when brought to a boil. Only 35% cream will not curdle when boiled. Usually, the soup recipe will say bring the soup to a simmer and add the milk just before serving. Another thing you can do is whisk one cup of cold milk into 2 tablespoons of flour and add this to the boiling soup. It will not curdle. I don't know the proportions of your soup but if it calls for 2 cups of milk than mix into 4 tablespoons of flour etc.... I usually thicken my cream soups with some potatoes and add more veggies than called for.
Skim milk should be okay to use, even though it is the most likely to curdle (due to low fat content). I'm just guessing (so correct me if I'm wrong!), but the recipe you have probably says to add the milk at the end after you take the soup off of the heat, i.e. just before serving. And if you're not planning to consume the whole batch right away, take out the portion you want and only add milk to that, leaving the rest milk-less to store in the fridge/freezer.
With regards to the oatmeal, not all fruit is acidic enough to cause curdling. And even when it is, it usually has to be quite a direct mixing of the acid and milk to make it curdle, e.g. orange -juice- mixed with milk. Whole strawberries, blueberries, etc. just (thankfully) won't do the same thing.
Hope this helps!