In the world of cheese, a starter, also known as a bacterial culture or starter culture typically consists of enzymes or other microorganisms, bacterial or mold spores, lactic acid (sometimes from the previous day's milk or whey) and natural elements. Two types of cultures are used: thermophilic cultures work best at temperatures over 100°F and mesophilic cultures function at temperatures between 70° and 100°F. Starters work by converting the milk's lactose (milk sugar) into lactic acid. This is done to balance the milk's acidity (pH level) so the casein (milk protein) will more readily coagulate into a curd when rennet is added. The type of starter contributes to a cheese's flavor, texture and other characteristics, depending on the style of cheese. For instance, Penicillium roqueforti in a roquefort starter produces this cheese's distinctive blue veins; Propionibacter shermanii is added to the starter for emmental to create its characteristic eyes; and Penicillium candidum or Penicillium camemberti in the starter of brie and camembert is what makes such cheeses ripen from the outside in, rather than vice versa. See also yeast starter
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.