Cut an apple and watch it brown: that is an enzyme working in front of you. A plain account of what enzymes are as molecules — the active site, activation energy, and why heat and pH change everything.
Cut an apple in half and leave it on the board. Within a few minutes the cut face turns from white to a dull tan. Nothing has landed on it and nothing has spoiled. An enzyme inside the fruit, brought into contact with air by the knife, has started rearranging colourless compounds in the damaged cells into brown pigments. It is one of the few chemical reactions in an ordinary kitchen that you can stand and watch happen.
That is a useful place to start, because enzymes are usually described in the abstract and they are not abstract at all. They are objects. They have shapes, they wear out, and they can be destroyed by a hot pan.
What is an enzyme?
An enzyme is a biological catalyst: a molecule that speeds up a particular chemical reaction without being used up in the process. Almost every enzyme is a protein — a long chain of amino acids folded into a precise three-dimensional shape. (A small number are made of RNA instead, which is why biochemists say "almost".)
The folding is the whole point. The chain does not sit in a loose tangle; it settles into one particular arrangement, held together by many weak interactions between its own parts. That arrangement creates a pocket or groove on the surface of the molecule, called the active site. The active site is where the chemistry happens, and its shape is what makes one enzyme different from another.
Living things run on enzymes because most of the reactions that keep a cell going would otherwise happen far too slowly to be of use. Every plant, animal, fungus and bacterium makes thousands of different ones. You can often spot an enzyme by its name: the suffix -ase is the modern convention, as in amylase, lipase, protease and lactase. Older names ending in -in survive from before the rule existed — pepsin, trypsin, papain, bromelain.
How an enzyme actually works
The molecule an enzyme acts on is called its substrate. The substrate fits into the active site rather as a hand fits a glove — the classic teaching image is a lock and key, though the modern picture is softer than that. The enzyme is not rigid. As the substrate arrives, the pocket adjusts around it and closes in slightly, a behaviour biochemists call induced fit.
Held in that pocket, the substrate is put under conditions it would never encounter drifting freely in solution. Two molecules that would have to collide at exactly the right angle are instead held next to each other in exactly the right angle. Chemical groups on the walls of the active site tug on particular bonds, straining them. The reaction proceeds, the products no longer fit the pocket properly, and they drop away.
This is also why enzymes are specific. A lactase will act on lactose and ignore the sucrose sitting next to it, because sucrose does not fit the pocket. Specificity varies — some enzymes are exacting, others accept a family of related molecules — but none of them are general-purpose. An organism that needs a hundred reactions needs roughly a hundred enzymes.
What activation energy means
Most chemical reactions that release energy still need a push to get started. Paper and oxygen will happily become ash and smoke, but a sheet of paper does not spontaneously ignite on the desk; it needs a match. That initial hurdle is the activation energy: the energy required to reach the awkward, strained, halfway state a molecule must pass through before it can become something else.
An enzyme lowers that hurdle. By gripping the substrate and stabilising the strained halfway state, it makes the transition dramatically cheaper to reach, so a far larger share of molecules manage it at ordinary temperatures. Heat does the same job crudely, by making everything collide harder. An enzyme does it precisely, at body temperature, to one reaction and not its neighbours.
An enzyme never makes a reaction happen that could not happen. It makes a reaction that would take years take seconds.
That distinction matters. Enzymes cannot bend thermodynamics or invent energy. They change the speed of a reaction, not its direction or its final balance point.
Why enzymes are not used up
A catalyst emerges from the reaction unchanged, which means the same enzyme molecule can turn over again and again. The rate at which it does this is its turnover number, and the figures are difficult to picture: a typical enzyme handles tens or hundreds of substrate molecules a second, and the very fastest known work through hundreds of thousands. A vanishingly small quantity of enzyme can therefore transform a great deal of material, given time.
They do not last forever — proteins degrade, and cells constantly manufacture replacements — but they are not consumed by the reactions they accelerate.
Where enzymes occur in food
Every raw ingredient that was recently alive carries its own enzymes, and their effects are familiar even when the word never comes up. Raw pineapple will not set in a jelly, because an enzyme in the fruit takes apart the gelatin protein that does the setting. Fresh ginger will curdle milk. Barley is deliberately sprouted before brewing so that the grain's own enzymes convert its starch into fermentable sugars. Cheese begins with rennet. Meat hung to age is being reworked by enzymes that were already in the muscle.
Fruit purées carry this kind of activity as a matter of course, which is simply a fact about fruit. Pineapple, mango and dark grape purée are among the ingredients listed on our concentrate; we list them because they are what is in the bottle, and for no other reason.
Enzymes in a fermenting vessel
Microorganisms face a practical problem: many of the molecules around them are far too large to bring inside the cell. Their solution is to secrete enzymes outwards, into the liquid, and let the chemistry happen externally — breaking long chains into fragments small enough to absorb. A fermenting vessel is therefore not just a container of microbes. It is a container of microbes and the enzymes they have released, acting on the ingredients around them.
This is the mechanism underneath every ferment, from sourdough to soy sauce. How that plays out over the course of an actual fermentation — what changes, in what order, and why the process has been used for thousands of years — is a separate subject, covered in what fermentation is.
Why heat denatures enzymes
Return to the folding. An enzyme's shape is held by weak interactions, not by anything sturdy, and that shape is the function. Add heat and you add motion; add enough motion and the weak interactions give way, the chain unravels, and the active site is gone. This is denaturation, and it is generally irreversible — the protein does not refold itself once it has come apart.
You have watched it happen. An egg white is a clear liquid of dissolved protein; in the pan it becomes white and solid, and no amount of cooling brings the liquid back. Nothing has burnt and no new ingredient has appeared. The proteins have simply lost their shape and tangled together.
Different proteins tolerate different temperatures, but as a broad rule the enzymes found in fruit and vegetables begin to lose activity somewhere above roughly 45 °C, and are effectively finished by the temperatures of cooking or pasteurisation. This is ordinary protein chemistry, and it applies to any food. It is also the plain reason a producer who does not want to cook the ingredients must keep the process cool: in our case the temperature is held below 45 °C for the whole cycle, which we explain in more detail on the production page.
How pH changes an enzyme's shape
Temperature is the best-known way to unfold a protein, but acidity does much the same work. The interactions holding an enzyme's shape depend on the electrical charges carried by its amino acids, and those charges shift as the surrounding pH moves. Each enzyme consequently has a range in which it performs best and outside which it slows, distorts and eventually denatures.
The ranges differ enormously depending on where an enzyme evolved to work. Pepsin, which operates in the stomach, is at home in strong acid and would be useless at neutral pH; most enzymes working inside a cell prefer conditions close to neutral. There is no universal optimum — only the conditions each particular enzyme is built for.
What an enzyme is not
It is worth being direct about the limits of this article, because enzymes attract a great deal of loose talk. Everything above describes what enzymes are as molecules and how they behave in a test tube, a plant cell or a fermenting vessel. It is general biology, the kind found in any textbook.
It is not a statement about what any enzyme in any bottle does inside a person. That is a different question, governed by different evidence and by European food law, and we do not make claims of that sort about our drinks. What we can tell you is what is in them, how they are made, and why the process is run the way it is. For anything beyond that, the honest answer is that we are a food producer, not a pharmacy.