Beer that’s unfiltered and unpasteurized (like real ale) still contains millions of live yeast cells in liquid suspension. With the help of gravity, and in due time, beer clarifies all by itself. But to expeditiously clear the beer of all this yeast, brewers use what are called finings.
A brewer adds finings to real ale when he racks or transfers the ale in its natural, unfiltered, and unpasteurized state into a cask. These finings basically clot yeast cells and other organic matter and drag them to the bottom of the cask, where they settle and form a jelly-like mass of sediment. When this happens, the beer is said to have dropped bright.
What finings do is fairly uncomplicated; what finings are is a bit more interesting. Here are two of the most common finings:
Carrageen: Also known as Irish moss, carrageen is a species of red algae found in abundance along the rocky shores of the Atlantic coasts of Europe and North America.
Isinglass: Isinglass is a form of collagen derived from the swim bladders of certain fish. After the bladders are removed from the fish, they’re processed and dried.
Not to gross you out, but prior to the introduction of the less expensive gelatin, isinglass was used in confectionary and desserts, such as fruit jelly and marmalade.
Other less-commonly used beer clarifiers include the following:
Albumen: Albumen is derived from egg whites. Dried albumen is rehydrated with water and added to the beer. Similar to gelatin, albumen is positively charged so it attracts negatively charged proteins and yeast.
Bentonite: Bentonite is a non-organic material combined with a form of fine powdered clay. When mixed with water, bentonite is very effective at clarifying liquids.
Gelatin: Gelatin is derived from the ground hooves of cows and horses. It’s a colorless, tasteless, and odorless water-soluble protein that attracts negatively charged proteins and yeast.
Pectinase: Pectinase is a general term for the various pectic enzymes that break down pectin, a jelly-like substance found in the cell walls of plants. Pectinase breaks down the pectin haze that can form in beer — especially those that contain fruit.
PVPP (polyvinylpolypyrrolidone): Say that five times fast! Also known by its commercial name, Polyclar is made up of minute plastic beads that are statically charged, thereby attracting particulate matter to themselves like electrostatic glue. (Pharmaceutical companies also use this product to produce capsule-type drugs.)
When a brewer adds finings to a cask of real ale, he may also add more hops and priming sugar. The extra dose of hops provides the beer with more hop aroma — not bitterness — and the priming sugar gives the yeast a little something to eat in order to create carbon dioxide within the cask. The cask is then sealed and shipped off to the pub.