Leaveners and Leavening

Terminology and definitions for bread types, bread ingredients, bread making and baking.

© 2011 by KV5R — Rev. April 15, 2011.

4. Leaveners, Leavening, and Related Terms


In bread baking, the process by which yeast converts sugar to carbon dioxide and alcohol. The carbon dioxide is trapped in the bread by the gluten fibers thereby expanding (rising) the bread.


Bacteria that exist in a symbiotic relationship with the wild yeast. During fermentation, they produce lactic and acetic acid (vinegar) along with CO2, creating the sourdough flavor. Various bacteria are used in bread, vinegar, cheese, sour cream, yogurt, etcetera, and are beneficial bacteria. In sourdough bread, the bacteria, along with the yeast, are killed during baking.


As a verb, to add leavening or to cause bread to rise. As a noun, an ingredient added to dough that causes it to rise through the release of CO2 through either a chemical reaction (baking powder), or yeast fermentation.


A leavening agent, usually dry yeast, a starter culture, or baking powder.


A batter-like mixture of flour, yeast and liquids that is made as the first fermenting step in some yeast bread recipes. Also called a preferment. Unlike commercial rapid-rise yeast, wild strains may take several hours to become active enough to rise the dough. A typical preferment sponge is made by leaving out half the flour called for in the recipe, allowing the sponge to rise and get bubbly for several hours, then adding the rest of the flour, then kneading and rising as usual. Don’t add salt or spices to the sponge, as they will inhibit growth. Add them afterward if needed, with the rest of the flour.

Sourdough Starter

A mixture of flour and water containing cultures of wild yeast and lactobacilli, used as a leavener. The term generally refers to either batter-like (mother) or dough-like (chef) consistency mixes which are retained from one activation or bake to the next. Some starters also contain potato, milk, yogurt, fruit, and other things.

Here are lists of Sourdough Bread Books and Sourdough Bread Recipes.

Common starter-related terms:

  • Amish Friendship: A sweet starter generally made with milk, sugar and flour used in a variety of baking goods such as quick breads, pancakes, muffins, coffee cakes, etc. Some versions of the starter are natural leavens, others are made with commercial yeast. “Friendship” refers to the tradition of baking more than enough bread and then giving some away, along with the recipe and some starter.
  • Biga: An Italian word for a yeasted starter. To make a biga, a tiny amount of commercial bakers yeast is mixed with water and flour to a dough-like consistency and fermented for a long period of time, 12 to 24 hours or more. It is then mixed into bread dough for leavening, often with the addition of more commercial baker’s yeast.
  • Chef: A French word for a natural leaven starter which is retained and used from bake to bake. Sometimes it refers to a piece of old dough saved off for the next bake, sometimes to a starter in its first stage, either a batter- or dough-like consistency. In classic French baking a “chef” is “built” (or “elaborated”) into a “levain” (a firm dough-like consistency) which is again built (or elaborated) into leavening for final bread dough. A piece of dough cut from a previous batch of bread which is used to make a levain or starter for the next bread. The chef is stored as a dough and may dry up on the outside but the inside will remain soft and ready to use.
  • Crocks and Jars: A small glazed clay container with a loose-fitting lid, traditionally used to store starters. There is no reason to store starter in crockery other than tradition. More convenient is a tall glass jar with a wire bail and glass lid with the seal removed. Any container may be used as long as (1) it is not metal (starters are acidic), and (2) it has a loose-fitting lid (to let gases escape).
  • Desem: A Flemish word for a natural leaven. A slowly fermented desem starter enhances the wheat flavor and creates a fruity, wheaty bread full of complex flavors. To make a desem, a small amount of freshly milled whole wheat flour is mixed with some unchlorinated water, then buried in a 10 pound bag of whole wheat flour, kept at cool temperatures (65 degrees F or lower) and allowed to ferment. It is refreshed every day or two for about 7 days until it is ready to make into bread. Burying the dough ball in the bag of flour allows the leaven to develop from only those yeast and lactobacilli which inherently thrive on the grain and avoids the introduction of other microbes.
  • Fresh: Starter which has been recently demonstrated to be vibrant and active. Starter in this category can raise plain white (french or white bread) dough to a “more than doubled” volume in less than 2½ hours after a single proofing (feeding) period, i.e. remove the starter from the refrigerator and proof once, then try using it. Starter which has been refrigerated for less than 5 days or so that was “fresh” before refrigerating is also fresh starter.
  • Fully Activated: That stage in the cycle of a starter of peak yeast and lactobacilli activity. A fully activated starter is full of large and small bubbles which are well-integrated throughout the starter (not just on top), there may be a layer of foam or froth on the very top and if the starter is a thick enough batter, it will have increased in volume by double or more.
  • Hooch: When the starter goes dormant in the refrigerator, the mixture separates, with the liquid rising to the top. The liquid is a mixture of water, alcohol and vinegar. The hooch should be nearly clear, not black or pink. Stir the hooch back in when you feed your starter, otherwise you will change the water:flour ratio of your starter.
  • Mother: Same as Refrigerator or Storage Starter. This is a batter-like starter of flour and water that is unrefreshed. See also Chef. Mother is similar to Chef—it depends on the consistency—mother is batter-like, while chef is dough-like.
  • Natural Leaven: A leaven of “wild” natural yeast and lactobacilli, as opposed to commercial baker’s yeast. Also includes leavens of natural yeast without lactobacilli. Natural yeasts are most easily collected by adding locally-grown (unwashed, organic) fruit peels (skins) to a starter, which are strained out after it starts.
  • New: Any starter started from any dry source (commercial or homemade), or the air, that has not yet qualified as “fresh starter.” This is not the same as “old” or “dead” starter, because these two conditions do not generally follow the same sequence of recovery stages.
  • Non-Standard: Starter which contains ingredients other than white flour and plain water, such as flour blends, potato or potato water, sugar, or milk.
  • Old Dough (Pate Fermente or Vielle Pate): A piece of final dough saved from one bake to the next. It differs from a starter only in that it is saved after the final dough has been mixed and therefore contains salt. Old dough can be used to leaven fresh dough. Depending on its age it may need to be either refreshed in order to strengthen its leavening ability or additional leavening may be used along with the old dough.
  • Old or Dead: Starter which has been previously demonstrated to be “fresh” but which is no longer fresh since it cannot be demonstrated that it can raise dough after a single proof as described above. Risings which take longer than 2½ hours indicate a starter that is either “new” or “old” depending on the prior life history of the starter. In nearly all cases “old” or “dead” starters can be revived back into “fresh” starters using the techniques described below.
  • Polluted: Starter which contains undesireable ingredients or cultures. Ingredients other than plain white flour and plain water change the habitat for the culture may or may not be desired. Normal starters should smell like a mixture of yeast, stale beer, and vinegar—but if they stink, like something rotten, they are probably contaminated with some toxic hydrogen sulfide-producing anaerobic bacteria, and should be discarded. This does not happen often. Other contaminants may include mold colonies or rotting animal infections caused by stirring starter with an unclean spoon, such as one that’s just been in raw egg, etc. Always mix and stir with a clean stainless spoon, or if a wooden spoon is used, wash and then microwave it until it steams.
  • Poolish: A French term for a sponge, a mixture of commercial baker’s yeast, water and flour. Usually a wet mixture rather than firm. Classically the water and flour are in a 1:1 ratio by weight, although in common usage the term now equates to “sponge”. Poolish may also refer to any starter or preferment that has a 1:1 weight ratio, and is seen in this context in many web postings.
  • Preferment: This term refers to any mix or starter that is allowed to ferment and build its leavening ability prior to being incorporated into final bread dough. This includes either a yeasted or naturally leavened sponge, a biga, a levain, a barm, a batter-like starter, old dough, etc. A pre-ferment contributes leavening and flavor to bread by allowing the dough longer periods of fermentation which enhances the texture and flavor of the bread.
  • Proofing: To proof a starter, you take a portion of it out of the refrigerator and feed it for a few hours to get a foamy “proof” that the starter is active.
  • Sour: A mother that has been refreshed with flour and water. As a noun, a starter used to build a sour-flavored bread dough, commonly used in commercial baking, for instance a “rye sour”.
  • Sourdough: Any live starter that contains both yeast (usually wild) and bacteria. The sour flavor is provided by the bacteria, which creates lactic acid (as in buttermilk) and/or acetic acid (as in vinegar).

Yeast, bread

In baking, “yeast” refers to single-celled fungi in the species Saccharomyces cerevisiae, which metabolizes sugars into carbon dioxide and alcohol, a process called fermentation. Yeast exists on plants, in air, in soil, and in and on humans and animals. Different strains of yeast are used for different processes, such as brewing and leavening. Live yeasts are not harmful to humans, except in the case of an opportunistic overgrowth of candida albicans (a normal gut flora), which causes candidiasis. Yeasts (including wild) used in breads are not harmful and, in any case, are killed during baking. Yeast is high in some nutritional trace elements, particularly selenium.

Here are some common terms related to bread yeast:

  • Active Dry: Tiny dehydrated granules of yeast that are in a dormant phase until they are exposed to water. This product was developed by the Fleischmann’s Yeast lab in Peekskill, New York for use by the armed forces during World War II. It is currently available from Fleischmann’s in a 3-packet strip and a 4-ounce jar.
  • Baker’s: Yeast used for raising bread, typically from the taxonomic group Saccharomyces cerevisiae.
  • Bread Machine: A Fleischmann’s Yeast product especially developed for use in the types of doughs most commonly made in bread machines. It is an instant yeast. Available in the U.S. and Canada in 4-ounce jars.
  • Brewer’s: Like baker’s, it is also Saccharomyces cerevisiae, but of many different strains that are optimized for brewing various alcoholic products. Brewer’s yeast will tolerate a higher alcohol content before die-off. See also Nutritional, below.
  • Commercial, Domesticated or Packaged: This is cultured Saccharomyces cerevisiae, the yeast that you can easily buy at the store.
  • Compressed: Fresh (not dried) yeast that is extruded and cut into a cake form. It must be refrigerated at all times and has a relatively short shelf life of 4-6 weeks.
  • Instant: Instant yeast is a specially processed form of Active Dry Yeast that can be mixed into a dough dry (rather than dissolved) and reduces rising time up to 50 percent. It was developed in the 1980s.
  • Nutritional: Similar to brewer’s yeast, is a deactivated yeast, usually Saccharomyces cerevisiae. It is available in the form of flakes, or as a yellow powder. It is popular with vegans and vegetarians and may be used as an ingredient in recipes or as a condiment.
  • Proofing: To dissolve yeast in warm liquid (¼ cup water) with a little sugar or honey (1 tsp) and set it aside for 5–10 minutes until it develops foam on top.
  • Quick-Rise: An “instant” yeast produced by Fleischmann’s in Canada and sold in Canada. It is ideal for dry mix methods of baking but can be used in any method.
  • Rapidmix: A yeast produced by Fleischmann’s Yeast and sold in Canada. It is similar to Fleischmann’s Active Dry Yeast sold in the United States; however, it is somewhat more finely granulated so that it can be mixed directly with dry ingredient.
  • Rapid Rise: An “instant” yeast produced by Fleischmann’s Yeast and sold in the United States in the convenient 3-strip packages for consumers. This yeast is well-suited to the quick, one-rise mix method of making yeast breads.
  • Traditional Active Dry: Active dry yeast produced by Fleischmann’s in Canada. This yeast should be dissolved before using for best results.
  • Wild or Natural: Saccharomyces exiguus (aka S. minor) is the yeast that is freely floating in air; on grains, fruit, and vegetables; and in soil. This is the yeast in sourdough starter. Wild yeasts are highly adaptive, and each locality has its own strains. Sourdough starters acquired from elsewhere will eventually convert to your local strains. Thus, sourdough breads from different regions will have flavors characteristic of that region. Unlike commercial yeast (S. cerevisiae), which likes an alkaline environment, wild yeast prefers an acidic environment, and so can survive the acids produced by the lactobacilli in sourdough starters.

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