Lemons, lime, and other unripe citrus fruit
They will eat certain sour foods, but don't really prefer them. They have been known to eat moderately sour foods, such as yogurt, without a problem, but will not eat lemons or other citrus. They generally stay away from sour drinks.
sour tasting foods are acids.
Some foods that are sour are lemons, grapes, and tamarind. Some types of oranges and some melon can also have a sour taste to them.
sour milk
yes
I have never noticed a sour taste in my dairy foods. You are possibly letting it get over date.
Citric Acid
lemon, lime, vinegar, sour sweets, unripened fruit,
acids
Some foods include yogurt, cheese, and sour cream
As long as it hasn't spoiled, it is okay as in small amounts occasionally. It is not really good for chickens to get a lot of moist foods, as it can sour their crops.
To make sour the foods !