Patrick Oconnell
Milk is made up of two types of proteins: casein and whey. When milk is spoiled, bacteria in the milk grow rapidly, causing it to become cheesy. This process can be sped up by adding an acid directly to the milk, such as vinegar, lemon juice, or citric acid, which will result in a cheese like ricotta, farmer's cheese, or paneer. This is known as direct acidification. Most cheeses, however, are made with indirect acidification, where bacteria are added to the milk, and it indirectly creates acid through the conversion of lactose to lactic acid. This process is also known as fermentation, and the resulting cheese is known as acid-set or sour milk cheese.
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What You'll Learn
How to make cheese from spoiled milk
Milk contains two types of proteins: casein and whey. When milk gets old, bacteria in the milk grow rapidly, causing it to become "cheesy". This process is known as fermentation, and it is the foundation of making most cheeses.
To make cheese from spoiled milk, you can clabber the milk with vinegar, lemon juice, or citric acid at a high temperature. This will result in a quick, easy cheese like whole milk ricotta, farmer's cheese, or paneer. These cheeses are known as direct acidification cheeses because you have added an acid directly to the milk.
Alternatively, you can make acid-set or sour milk cheese by curdling the milk with lactic acid bacteria or by adding an acid. This type of cheese is technologically simple to produce and accounts for around 25% of cheese production. Examples of acid-set cheeses include queso blanco, quark, and cream cheese.
Another option is to add rennet, an enzyme found in calf stomachs, to separate the whey. You will then need to drain the sugar from the milk curd via osmosis and press it into a wheel of cheese several times at varying pressures. Finally, age the cheese for several months, brushing off any mould a few times a week.
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The difference between sour milk and spoiled milk
Milk contains two types of proteins: casein and whey. When milk goes bad, it can be described as either sour or spoiled, but there is a difference between the two.
Spoiled milk usually refers to pasteurised milk that smells and tastes off due to the growth of bacteria that survived the pasteurisation process. These bacteria are not considered health-promoting and could make you sick. Spoiled milk has soured accidentally.
Sour milk, on the other hand, often refers specifically to unpasteurised, raw milk that has begun to naturally ferment. The fermentation of raw milk occurs due to various species of lactic-acid-forming bacteria, a small percentage of which are considered probiotics and may offer minor health benefits. Sour milk is milk with a tart taste, which the milk gets either because it is beginning to spoil or because it was soured intentionally through fermentation or acidification. The terms 'sour milk' and 'soured milk' are often used interchangeably, which is confusing. Technically speaking, there is a difference between sour milk and soured milk: milk that is soured on purpose is 'soured milk', whereas milk that turns sour on its own is 'sour milk'.
The initial pH level of fresh milk is around 6.5, which is slightly acidic. This varies by species, with goat milk being a little less acidic than cow milk. When making cheese, ingredients are added to make the milk more acidic, thus making it sourer. This souring process is also known as fermentation. And sour milk eventually curdles and separates, leaving us with curds and whey. This souring process can be done with pasteurised milk or raw (unpasteurised) milk, but the amount of culture or bacteria needed might differ depending on which you use.
Acid-set or sour milk cheese is cheese that has been curdled (coagulated) by natural souring, often from lactic acid bacteria, or by the addition of acid. This type of cheese is technologically simple to produce. When making soft acid-set cheese using bacteria, the coagulum results from the production of lactic acid by the starter microorganisms.
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How bacteria in milk creates cheese
Milk contains two types of proteins: casein and whey. When milk gets old, bacteria in the milk grow rapidly, causing it to become "cheesy". This process is known as fermentation, and it can be done with pasteurised or raw milk.
Cheese is made by adding ingredients to milk to make it more acidic, which causes it to curdle and separate into curds and whey. This can be done by adding an acid directly to the milk, such as vinegar, lemon juice or citric acid, or by adding bacteria to the milk, which indirectly creates acid through the conversion of lactose to lactic acid.
When making soft cheese using bacteria, the bacteria produce lactic acid, which causes the milk to coagulate. This method of coagulation accounts for around 25% of cheese production and is used to make fresh cheeses such as queso blanco, quark and cream cheese.
Rennet, an enzyme found in calf stomachs, can also be added to milk to separate the whey. The sugar is then drained from the milk curd, and the mixture is pressed into a wheel of cheese. The cheese is then aged for months, and any mould is brushed off a few times a week.
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How to make acid-set cheese
Spoiled milk is not a type of cheese, but it can be used to make cheese. Acid-set cheese is made by curdling milk through the addition of acid or by natural souring, often from lactic acid bacteria.
To make acid-set cheese at home, you will need to follow these steps:
- Prepare the milk for making cheese by boiling it for 15 minutes or longer. The amount of milk in the recipe will be 1 gallon, but the end product will be 1/2 to 1/3 of the volume of the milk, depending on the type of milk used and the amount of whey produced.
- Cool the milk down to lukewarm.
- Add a spoon or two of your mother cultures (ready yogurt from the first batch) or acidify the milk directly by adding gradually and carefully some lemon juice, white vinegar, citric acid or rennet. The amount could vary from a few drops to a teaspoon of citric acid. It is wise to use the least amount of acid possible to avoid an excessively tangy flavour.
- Allow the milk to separate into two halves – curds and whey. This can happen if you simply do not stop the yogurt mix after it is set and patiently await the separation.
Acid-set cheese is technologically simple to produce and accounts for around 25% of cheese production. These are generally fresh cheeses like queso blanco, quark and cream cheese.
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How to make cheese without rennet
Spoiled milk is not a type of cheese, but it can be used to make cheese. The process of making cheese from milk involves adding ingredients to make the milk more acidic, which causes it to curdle and separate into curds and whey. This souring process is also known as fermentation.
Ingredients
- Milk
- Cream (optional)
- Salt
- Lemon juice or vinegar
Method
- Pour the milk and cream (if using) into a saucepan.
- Bring the mixture to about 120 degrees Fahrenheit (or 200 degrees Fahrenheit if not using cream).
- Add the lemon juice or vinegar. The mixture should start to separate.
- Stir the mixture and then let it sit for 15-30 minutes.
- Gather the curds and separate them from the whey.
- If desired, add salt to the curds.
- Press the curds into a ball and squeeze to remove any remaining whey.
Tips
- You can adjust the milk-to-cream ratio to change the consistency of the cheese. More cream will make it creamier.
- You can also use cheesecloth to help remove the whey.
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Frequently asked questions
Spoiled milk is not a type of cheese, but it can be used to make cheese. The process of making cheese involves adding ingredients to milk to make it more acidic, which causes it to curdle and separate into curds and whey.
Ingredients such as vinegar, lemon juice, or citric acid can be added to milk to make it more acidic. This process is known as direct acidification.
Cheeses such as whole milk ricotta, farmer's cheese, and paneer are made through direct acidification.
