Why does not the milk curdle?

The curdling of milk is usually one of the problems that many amateurs find when making cheese in their homes. The causes are very diverse and we will try to offer a guide of possible causes that help to identify the problem and to solve it.

Let's start by explaining the curdling process that has three main methods:

Enzymatic coagulation: it is produced by the addition of an enzyme to milk. The enzymes can be of animal, vegetable or microbial origin. The most common is the combination of chymosin and pepsin that is extracted from the stomach by lactating ruminants. The coagulation by this rennet is affected by the temperature. In this way, with a temperature of up to 20 degrees, coagulation is very slow. Above 20 degrees increases until it reaches its maximum at 40-42 degrees Celsius. From that temperature it decreases to 65 degrees where when the temperature increases, coagulation becomes impossible.

Lactic acid coagulation: it is produced by the addition of a mineral or organic acid to the milk and when a pH of 4.6 is reached, a granular curd is produced. It is also produced by the development of lactic bacteria with milk at rest (thermophilic cultures).

Mixed coagulation: it is the combination of the two previous ones.

When we meet customers who have settling problems there are always checkpoints that we try to check. They are in particular the following:

    Quality of milk when making cheese
    Process temperature
    Amount of calcium chloride added
    Quantity of rennet added
    Dissolution in water, if applicable, of chloride and rennet
    Time

Quality of milk when making cheese

Of all the previous ones, perhaps the most important one is the quality of the milk. All those who have been making cheese in their homes for some time have discovered the difference between using one milk or another. In general terms it is necessary to use milk that is not UHT (Ultra High Temperature). In general, the necessary milk can be found in refrigerated supermarkets. Within the milk that we find in the refrigerated area there are qualities that make them more or less suitable for use in the production of cheeses. If you are lucky enough to be able to access raw milk or pasteurized milk that comes directly from the farmers, you will not have any fruit set problems. A very useful alternative is the hydration of whole milk powder that allows to modulate the density of the milk and the tasty of the result. In general terms, the less appropriate milk is, the more we need: chloride, rennet, time and temperature.

Surely someone will ask, and how do I know the quality of the milk? The answer is trial and error. It does not exist, and of course we will not create, a ranking of milk qualities for cheese production. But we encourage you to try different milks. The production of cheese does not stop being an exercise of trial and error until the favorite combination of factors is achieved.

Process temperature when making cheese

The temperature is another relevant point at the time of setting. Normally the rennet is added when the milk is at a temperature of a range of 20 to 40 degrees. The temperature decided depends on the final cheese you want to obtain. Its control and maintenance are important. Sometimes it is necessary with experience to increase or decrease the temperature to obtain the desired result. The ideal in terms of temperature is to start at the set temperature and maintain it for setting. The bain marie is a good method throughout the cheese making process and especially at this point.

Amount of calcium chloride added

Calcium chloride is one of the elements that milk loses in the pasteurization process. Its addition to milk tries to restore that loss. Its restoration makes the milk recover its curdling capacity. Its addition or its natural presence reduces the pH of the milk and accelerates the curdling process while strengthening the consistency of the same. The standard doses per liter of milk are the following:

    Calcium chloride in flakes: 5 grs or 1 teaspoon of coffee x liter of milk
    Calcium chloride liquid: From 1Ml to 2ML diluted in 5 to 10 times of water (1ML = 12/15 drops)

The recommended standard measures should be modified according to the observation of the "quality" of the milk used.

Amount of rennet added to milk

The rennet can be of animal, vegetable or microbial origin. At present, the gene for chymosin has been reproduced in the laboratory, so it can also be "synthetic".

The rennet mixture of chymosin and pepsin is a liquid extract from the maceration of the rennet of young ruminants in a brine of 10%. More or less the composition is 75% / 80% chymosin. The curdling force is usually presented by means of a formula that relates the volume of the milk, the rennet and the clotting time. In this way a value F = 104 means that 1 liter of rennet coagulates 10,000 liters of milk, in 40 minutes and 350.

Therefore, the values ​​to be added are those established by the manufacturers. In general terms, the recommended amounts are the following per liter of milk:

    Powdered rennet: ¼ teaspoon of coffee
    Liquid rennet: 0.5ML or 6/7 drops

These values ​​should be adjusted to the reality of the quality of the milk and the required result in terms of the strength of the fruit set.

Dissolution in water, if applicable, of chloride and rennet

It is normal that both the liquid chloride and the rennet in all its versions are diluted in cold water (but previously boiled) before adding the result to the milk. The reason is none other than to facilitate uniform mixing with milk. Do not neglect this aspect.


Times in cheese making

As we saw in the rennet point, time is important. Our recommendation is that if the fruit set is weak for any of the above reasons without having identified it, we will give it the time it takes to make it, and that if it should normally set in one hour, we leave it as long as necessary in a warm place. Keep in mind that the temperature directly affects the fruit set so you should take it into account at the time of adding it but also during fruit set. The ideal thing is to keep the tub in the water bath.

If none of this works and after reviewing all the points you have two options:

    Change the milk that is the most reasonable option
    Go to a mixed coagulation by adding citric acid (lemon) or vinegar.

We hope that with this post we have solved some doubt about the curd process and every time make richer cheeses.

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