Enzymes are magnificent things. An enzyme is a protein – a long string of amino acids folded up in a complex and specific way – that causes a reaction to happen. Most of them are catalysts, so they aren’t changed by the reaction. The reactants attach to the enzyme, which changes them enough to make them react, and the products fall off, leaving the enzyme as it was in the first place.
The really interesting thing about enzymes is how efficient they are. They are really, really good catalysts. Several thousand times faster than the reaction would otherwise be in some cases. Nature and evolution have given us some amazing things. Haemoglobin (which isn’t technically an enzyme, it’s a transport protein) is very delicately tuned to have the correct binding strength with oxygen. People have been trying for years to duplicate the “active site” where the oxygen is transported and we can’t do it. Without the whole surrounding protein structure, the iron doesn’t bind oxygen at all, or it binds it irreversibly, or it dimerises around the oxygen – there are several common failure modes, but every time we solve one we encounter another. We can’t make a simple thing that does the same job as the immensely complex natural protein that our cells synthesise every day.
Enzymes are as bad. Duplicating their effects is very difficult. There’s a whole field of chemistry all about mimicking natural proteins and enzymes. It’s called biomimicry and it exists because simple chemistry, the kind you can do in test tubes (and kitchens) is messy, inefficient and unreliable compared to what nature can do. To turn sugar into alcohol by chemical methods would be a real challenge. Doing it with yeast is just a matter of adding a bit of water and not heating it above about fifty degrees, it’s easy, it’s reliable. The enzymes in the yeast will do what they always do and you will end up with the desired products, every time, and with hardly any energy required.