Sour and Spoiled Milk: Understanding the difference and uses

While drinking a cup of fresh milk that has soured does not sound appealing, there are benefits to using soured milk in your kitchen! There are many milk products that can be made from soured milk found in the back of your fridge, so let’s reduce our food waste and make the most of some otherwise bad milk! 

Firstly, it’s important to know the difference between sour and spoiled milk. In short, spoiled milk is commonly grocery store milk that was forgotten for an extended period of time and there’s potentially harmful bacteria. Sour milk has been intentionally acidified through bacterial cultures. This type of milk in the raw milk world has beneficial bacteria that produces lactic acid to give milk a tangy flavor. 

What is sour milk?

Sour milk is milk with a sour taste, sour flavor, and sour smell. In the raw milk world, fresh milk is slightly acid with a pH around 6.5. When milk is soured intentionally by fermentation decreasing the pH to make milk more acidic. Sometimes this is done to make cheese, a bread recipe may call for sour milk, or it just happens naturally when you’ve got multiple mason jars or milk in the fridge.  

What is spoiled milk? 

Spoiled milk is milk that has gone bad, typically referring to store bought “regular milk” that is past the expiration date and beginning to smell. In the raw milk world, it’s a different story: we will just use the sour milk for a different purpose! 

Raw Milk vs store bought milk

While store bought milk does not have any of the harmful bacteria present, the carton of milk is also lacking all of the beneficial bacteria. Ultra-pasteurized milk has been heated to such a high temperature (sometimes it’s even shelf stable) it is likely it will not ferment, even with a leavening agent. Raw milk never goes bad because the good bacteria will culture the milk to begin the souring process. While it may not sound or smell appealing to drink, it’s a great option for baking or marinating. 

Store milk ages differently since the pasteurization killed all of the good and bad bacteria. 

Read more about raw milk benefits in our other post here

More science behind sour milk

Soured milk is not only more acidic but the lactic acid bacteria has converted the sugars, meaning it has less lactose! Additionally it will have less sugar so a tangy taste and thickness. This extra acidity is what makes it great for baking. 

Types of soured milk:

Any of these methods are ways to sour milk. Some are quick methods, which may not have all of the health benefits but will still provide slight tang in whatever recipe you need. 

• kefir grains- these grains are a live yeast and good bacteria added to milk to culture the milk. You can reuse the grains over and over like keeping a sourdough starter
• buttermilk- here I am meaning a specific culture that is used to ferment milk, not the leftovers from making butter! Though do use the leftover liquid from butter making! 
• acidification- such as adding lemon juice at 1 T per cup of milk. This is not considered as beneficial as the fermented dairy products, but is still a great idea if you are needing soured milk quickly!  
• clabbered milk- leave raw milk on the kitchen counter at room temperature for 12-24 hours and let it turn thick! The good bacteria in the raw milk will take over and serve as the natural starter. After your first batch you can save it to restart the fermentation process next time! You can make sour cream (or soured cream as we call it) by clabbering the heavy cream from raw milk. 

How to use soured milk

Soured milk is usually called for in the following ways:

• baked items and quick breads. The most common: Sour milk pancakes, cornbread, muffins, biscuits and scones 
• marinating meat like chicken
• cheesemaking: many types of cheese like farmer’s cheese and and cottage cheese call for soured milk! 

How to make soured milk

You can raise the acidity of milk to make soured milk (store-bought or raw milk) in the following ways:

• add a culture like Kiefer grains or buttermilk from a previous starter 
• Add lemon juice or lime juice: 1 tablespoon per 1 cup of milk 
• let your store-bought milk sit (in the fridge) past the sell-by date 
• set your raw milk on the counter and let the warmer temperatures work their magic to turn it into curdled milk over about 12-24 hours. in our opinion, this is the best way! 

Buying and using local, raw milk

Most places that sell raw milk in the USA are selling raw, whole milk with the cream on top. The best kind of milk! In Iowa, it seems like $8 a gallon is pretty common. Since raw milk has an average shelf life of about 10 days, you may start to smell an unpleasant smell after that timeline. Since it’s probably time for another local milk pickup, whatever is leftover is a great way to begin experimenting with soured milk! If you are a dairy farmer with a stack overflow of enough milk, consider emptying out your fridge and acidifying your milk with the methods above and making something! 

If you are trying raw milk for the first time, it may take time for your gastrointestinal tract to adjust to the probiotics in raw milk. The milk tastes so delicious, but be sure to limit yourself in the beginning as you adjust to the change! Personally, I always through I was lactose intolerant but I can fill up a jar with raw milk and drink the whole thing! 

FAQ’s:

Will sour milk give me food poisoning? 

Milk that has become slightly acidic will not give you food poisoning. If milk has mold or smells repulsive, do not drink it. 

Where can I find raw milk? 

Search on local Facebook groups or rawmilk.com to find raw milk near you! Our farm offers raw milk on a subscription program. Sometimes you will see raw milk being sold as a herd share as the sale of raw milk is not allowed in some areas. 

If you are local to our farm, feel free to contact us and see if we have room in our milk subscription program!