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Consistency | Causes of Coagulation | Prevent clotting | Reverse clotting

Protein coagulation

Precipitation, flocculation, denaturation, curdling, coagulation, congestion, clumping

Proteins can coagulate, which is the most important technical property for our kitchen. What does coagulation mean?
Proteins are usually readily soluble in water or bind water themselves. If this property is abolished or lost, then, it is said, “the proteins fall out” (they coagulate, denature, stagnate, etc.). They become stronger and are then no longer dissolved in water (or water is no longer bound by the protein). The coagulation is irreversible, so it cannot be reversed.

  • Milk that is added to hot tea or coffee can curdle when it is a bit older, and it becomes "cheesy"
  • In a raw egg, protein is dissolved in water - both in the yolk and in the egg white. When the egg is cooked, the egg whites coagulate and set
  • In the case of a bleeding wound, a firm crust of coagulating proteins forms after a while to close the wound


Important for our kitchen: the coagulation changes the consistency of the protein. First the tangled strands of protein wind up and form long threads. These threads then connect with each other and form a soft, sponge-like or even firm to tough structure (gel).

In practice it can look like this:

  • Small solid protein clumps can form in a liquid - these can make the liquid more creamy (binding)
  • Liquid containing protein can have a firm, soft, spongy (egg milk) or soft, crumbly (boiled egg yolk) structure
  • In dough, coagulated protein (from the flour / glue) helps to make baked goods such as bread or rolls firm
  • On a pizza, cheese containing protein first becomes soft, then hard and crispy - a crust forms

Causes of Coagulation

There are several factors that can trigger or support the clotting of proteins. The most important ones for our kitchen follow here - factors such as UV radiation and others can also play a role.


From approx. 50-60 ° C many proteins coagulate. Incidentally, the amino acids that make up the protein are not so badly endangered by heat, so they remain valuable to health.
It is important that the coagulation occurs through heat process is - so it is not the case that the proteins of an ingredient suddenly coagulate at a certain temperature. Rather, coagulation is a longer, so to speak, stepless process that depends on temperature and time.
The coagulation of the proteins in the chicken egg begins at approx. 60 ° C and is only completed at a temperature of approx. 85 ° C.
Some proteins, such as milk proteins or certain enzymes, can be quite heat-stable under certain conditions and even withstand temperatures of 100 ° C and more without coagulating - otherwise you would not be able to cook milk or cream without it curdling


Proteins can coagulate if they come together with acid or with acidic ingredients such as vinegar. A well-known example of the use of this type of coagulation are types of cheese such as sour milk, whey or grilled cheese or tofu.
The coagulation of older milk or cream when heated is caused by acid, because the lactic acid content increases with age due to lactic acid fermentation.
Acid has a similar effect to heat: the higher the acid dose, the greater the effect. The effects of acids, for example when marinating, therefore have similar effects on protein as a very light cooking process. However, the duration is several hours or even days.


Salt has a similar effect on protein as acid - it weakens the binding of the proteins to the water they bind. As a result, further coagulation can now take place more easily. This is probably the reason for the tip when preparing scrambled eggs to only salt the egg at the last moment: this way, the water-binding ability of the protein is not affected; The scrambled eggs can - provided they are carefully heated - become particularly rich in water and thus "creamy".


Proteins can coagulate when they come together with alcohol. In order for alcohol to be effective on its own, i.e. without any other coagulant factors, it must be very concentrated - over 50%.


Certain enzymes, although they are proteins themselves, attack or break down other proteins.
In the production of cheese, the enzyme rennet is used to curdle milk. Some enzymes found in fruits, such as pineapples and kiwi, break down proteins, which can lead to a bitter taste.

Prevent clotting

Of course, by avoiding the factors described above, the coagulation of proteins can be prevented or delayed. In addition, the presence of certain substances such as emulsifiers or the combination with other substances such as calcium can increase the stability of protein.

Reverse clotting

Under normal circumstances, a coagulation cannot be reversed - once it has coagulated, it is forever. However, the coagulated protein compounds can be mechanically broken up so that they are no longer noticeable. A good hand blender, for example, is helpful.