What are enzymes and why are they so important in cheese making?

Last week, intrigued by what I had related in the previous article , I wanted to try making homemade gorgonzola. Because I am lazy, instead of going to the pharmacy or supermarket to buy rennet, I used liquid rennet that had been given to me some time ago, even though the person who gave it to me warned me that it had been out of the refrigerator for a long time. I had no guarantee that it would work, in short.

Aware of the risk, I set to work. As I feared, adding small amounts of rennet was not enough and I had, therefore, to add much more. Despite copious additions, milk protein coagulation was only partial and produced very small and difficult-to-treat clots. Of course, as a first experience of home cheesemaking, let’s say it is not very successful. But we can learn some lessons from it, and we can take the opportunity to brush up on enzymes.

Rennet, in fact, is a mixture of enzymes that can cut certain proteins in milk, causing it to coagulate. The main components of rennet include chymosin and pepsin, two proteases, i.e., enzymes that cut proteins (milk caseins, in this case). But what are enzymes? What role do they play within the complex metabolic mechanisms?

What enzymes are and what they are used for

Enzymes are often referred to as biological catalysts. In chemistry, a catalyst is a substance that can accelerate chemical reactions, that is, make them happen faster than they would in their absence. It is a bit like a chemical reaction is a transalpine journey: if I want to cross the Alps and go to the other side of the mountain, I have two options in front of me. I can go up, up, to the top of the mountain, pass a pass and come back down the other side, or I can opt for a tunnel, a tunnel that goes through the whole mountain and comes out on the other side. Which of the two options do you think is faster and more energy efficient?


Enzymes are able to make chemical reactions easier and faster even at low temperatures. Some reactions, at these temperatures, would never happen without the help of an enzyme, or they would take an extremely long time. But what are these wonderful catalysts made of?

How enzymes are made and the importance of proper food storage

Almost all enzymes are proteins, that is, longer or shorter chains of linked amino acids*. These chains of amino acids fold in space and take different shapes, mostly globular, as if they were strands of wool that are rolled up to form a ball of yarn. The shapes they take can also be very complex, and the fascinating thing is that they almost always manage to fold correctly on their own.


Taking the right shape is crucial for proteins, which can do their innumerable jobs inside cells are if they fold well, while proteins with incorrect shapes can give rise to various diseases, such as Alzheimer’s, Parkinson’s or mad cow disease.

As we move from a linear to a curled form, we see an interesting phenomenon in protein chains: some amino acids that were previously far apart now come to be found close together. And that’s how the magic happens: some of these amino acids can now work together, helping each other to catalyze chemical reactions. The so-called “active site,” that is, that region of the protein where the substances to be transformed (the “substrates”) are bound and where the reactions leading to the products occur.


The amino acids working in the active site cooperate through very delicate balances. All it takes is for them to shift by just a few nanometers** or for the acidity of the surrounding environment (its pH) to change slightly, that the enzyme may no longer work as well as before, or inactivate altogether. That is why it is very important that we follow the manufacturer’s directions, storing the enzyme in the correct way and enabling it to work to its full potential. Not doing so, as it was in the case of my rennet, abused by time and temperatures, can lead to its suboptimal functioning, with results that are less than expected.

Enzymes are really tiny, amazing machines, capable of helping us in our activities, such as producing food, but most of all essential for keeping us alive. It is only because of the countless enzymes working within our bodies that we are able to breathe, feed ourselves, defend ourselves, move, think and even understand, in part, how beautiful and complex life is.

*There are also enzymes formed from RNA with catalytic properties, which are called ribozymes

**the nanometer is a unit of length, and corresponds to one billionth of a meter, which is a million times smaller than a millimeter

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