Acids
Acids are very important in wine making, affecting both the fermentation and the finished taste. A wine that lacks acid tastes dull or flat. Lowering the pH (adding acid) adds life and sparkle to the wine. Correcting the acid level of a wine can be the difference between an unpalatable wine and a masterpiece.
Enzymes
Enzymes are molecular catalysts, typically speeding reactions and lowering the required temperature to achieve them. Pectolase is the most commonly used enzyme in wine making — it speeds and maximises the colour extracted from plants and fruits. Amylase is a starch destroying enzyme that breaks down starches into fermentable sugars and destroys haze forming compounds.
Sterilizers
All brewers and vintners need some method of cleaning equipment and killing foreign bacteria. Depending on your task and equipment, there are various chemicals that can help.
Campden tablets and sodium metabisulphite (same active ingredient) are yeast inhibitors that prevent bacteria from growing and slow oxidation. They do not clean dirty equipment, and must not be used on stainless steel as they can cause surface corrosion.
Chlorine based products both kill yeasts/moulds and help to clean. The drawback is that chlorine must be rinsed very thoroughly as it has a strong taste and ruins head on beer.
No Rinse sanitizers based on sodium carbonate peroxide kill germs and then sublimate, so rinsing is not important.
Finings
Finings are solutions or powders that distribute charged particles when added to liquid. These particles conglomerate dead yeast cells and other undesirables, which then precipitate and settle to the bottom of the container. Finings speed the time it takes to clear both wine and beer.
While not strictly a fining, Irish Moss operates in a similar way and is added near the end of the boil in full mash beer making.
Active Carbon (Activated Charcoal) can remove undesirable odours and tastes from liquid. Its massive surface area allows absorption and fast reaction speeds. Very useful to remove the by-products of high alcohol yeasts.
Nutrients
Yeasts require food to live. Water and sugar are enough to get yeast cells to grow and ferment, however to keep a yeast colony healthy and ensure it can ferment to its potential, certain trace elements are beneficial. Nearly all yeast nutrients contain diammonium phosphate; the more advanced contain blends of amino acids and vitamins as well.
Water Treatment
Balancing the dissolved solids in the mash liquor is an essential part of advanced brewing. Whether increasing the carbonates in light bitters or decreasing the pH for a Pilsner, you'll find the chemicals here.
General Chemicals
Useful chemicals that don't fit the other categories but are helpful anyway. They include Tannin, Precipitated Chalk, Potassium Sorbate and others.