Re: wich milk spoils the fastest one percent, two percent, whole milk, skim milk

Good question!

The amount of fat may have some small effect for two reasons, which I will explain below. However before I go into those details, I want to point out that the most important factors in milk spoilage are the temperature the milk is stored at and the number of bacteria in the milk to start with.

Now, fat may play some role for two reasons.

When bacteria grow in a food they break down certain molecules to use for their own food. As a result of this breakdown, certain other molecules are formed. Those other molecules might be ones that smell bad to us. Many spoilage breakdown chemicals (i.e. the ones that smell really bad) are formed from fats… so more fat might mean more breakdown chemicals, which might mean faster spoilage.

Also some types of bacteria like to use fats for food, so more fat might mean more food, which would mean faster spoilage.

In a practical experiment, lets say you took one carton each of one percent, two percent, whole milk, and skim milk an set them out on the counter. Let’s also say you observed them carefully to see which one spoiled faster. Slight differences in the number and type (species) of bacteria would make it very difficult to see the real effect of the percent fat on the time to spoilage.

The bottom line is that to keep milk fresh for as long as possible make sure your fridge is at 40 F or below!