More than 50 additives are permitted in American beer, including preservatives, foaming agents (usually vegetable gums), and enzymes—similar to meat tenderizers—that break down proteins into smaller molecules that are less likely to cloud the brew. Some companies avoid the use of preservatives, and usually advertise this fact on the label.
From the book On Food and Cooking (2nd edition) by Harold McGee. © 2004 Harold McGee.
By permission of Scribner, a division of Simon & Schuster, Inc.