Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and related products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described A leavening agent (sometimes called just leavening or leaven) is a substance used in Doughs and batters that causes a foaming action intended Baking is the technique of prolonged Cooking of Food by dry heat acting by conduction, and not by radiation, normally in an Oven, Bread is a Staple food prepared by Baking a Dough of Flour and Water. Fermentation in Food processing typically refers to the conversion of Sugar to Alcohol using Yeast under Anaerobic conditions Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Dough is a paste made out of any Cereals (grains or leguminous crops by mixing the Flour with a small amount of Water. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single The use of potatoes, water from potato boiling, eggs, or sugar in a bread dough accelerates the growth of yeasts. The potato is a Starchy Tuberous crop Vegetable from the perennial Solanum tuberosum of the Solanaceae An egg is a round or oval body laid by the female of many animals consisting of an Ovum surrounded by layers of Membranes and an outer casing which acts to nourish Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Salt and fats such as butter slow down yeast growth. For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water Butter is a Dairy product made by churning fresh or fermented Cream or Milk. The majority of the yeast used in baking is Saccharomyces cerevisiae, the same species commonly used in alcoholic fermentation. Saccharomyces cerevisiae is a Species of Budding Yeast. It is perhaps the most useful Yeast owing to its use since ancient times Fermentation in Food processing typically refers to the conversion of Sugar to Alcohol using Yeast under Anaerobic conditions Additionally, Saccharomyces exiguus (also known as S. minor) is a wild yeast found on plants, fruits, and grains that is occasionally used for baking; it is not, however, generally used in a pure form, but comes from being propagated in a sourdough starter. Sourdough (or more formally natural leaven or Levain) refers to the process of leavening Bread by capturing wild Yeasts

Use and effects

When yeast is used for making bread, it is mixed with flour (often but not always a wheat flour), salt, and warm water (or milk). Wheat ( Triticum spp is a worldwide cultivated grass from the Levant area of the Middle East. The dough is typically kneaded until it is smooth to mix the ingredients and develop gluten, and then left to rise, sometimes until it has doubled in size. Gluten is a composite of the proteins Gliadin and Glutenin. These exist conjoined with Starch, in the Endosperms of some Some bread doughs are knocked back after one rising and left to rise again; this redistributes some of the yeast's food supply and prevents gas pressure from rupturing the starch/protein matrix of the dough. A longer rising time gives a better flavour by allowing more fermentation products and by encouraging bacterial fermentation, but the yeast can fail to raise the bread in the final stages if it is left for too long initially. The dough is then shaped into loaves, left to rise until it is the correct size, and then baked, sometimes with a portion of the dough retained by the baker for the preparation of the next batch.

A weak solution of water and sugar can be used to determine if yeast is expired. Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as When dissolved in the solution, active yeast will foam and bubble as it ferments the sugar into ethanol and carbon dioxide. This is generally referred to as proofing the yeast as it gives proof of the viability of the yeast before the other ingredients are added.

Baker's yeast is generally used in one of two ways. The direct method involves adding the yeast directly to the dough; alternately, a trace amount of yeast can be allowed to propagate through a small fraction of the dough, a longer-established technique known as a sponge or preferment. A pre-ferment (pâte fermentée also called a "sponge" or a "bread starter" is a Fermentation starter used in Bread Baking. The former method is widely used in breads where flavor comes from additives such as milk, eggs, or sugar, as well as for automated processes such as bread machines and industrial baking; the latter derives from older methods such as sourdoughs and old dough starters and is preferred for breads with relatively short and additive-free ingredient lists.

History

A block of fresh yeast.

It is not known when yeast was first used to bake bread. The first records that show this use came from Ancient Egypt. ^[1] Researchers speculate that a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of the flour caused it to ferment before baking. The resulting bread would have been lighter and more tasty than the normal flat, hard cake. It is generally assumed that the earliest forms of leavening were likely very similar to modern sourdough; that is, the leavening action of yeast would have been discovered from its action on flatbread doughs, and would either have been cultivated separately or transferred from batch to batch by means of previously mixed ("old") dough. Sourdough (or more formally natural leaven or Levain) refers to the process of leavening Bread by capturing wild Yeasts Alternately, the development of leavened bread seems to have developed in close proximity to the development of beer brewing, and barm from the beer fermentation process could also be used in breadmaking. Beer is the world's oldest and most widely consumed Alcoholic beverage and the third most popular drink overall after water and tea Barm is the foam or scum formed on the top of liquor (ie fermented alcoholic beverages such as Beer or Wine, or feedstock for Hard liquor

Without a full understanding of microbiology, early bakers would have had little ability to directly control yeast cultures, but still kept locally interesting cultures by reusing doughs and starters to leaven later batches. Microbiology (from Greek grc μῑκρος mīkros, "small" grc βίος bios, " Life " and grc -λογία However, it became possible to isolate and propagate favored yeast strains in the same manner as was done in the beer industry, and it eventually became practical to propagate yeast in a slurry with a composition similar to beer wort, usually including barley malt and wheat flour. WORT (899 FM is a listener-sponsored community radio station broadcasting from 118 S Such cultures (sometimes referred to in old American cookery as "emptins", from their origins as the dregs of beer or cider fermentation) would become the ancestors of modern baker's yeast, as they generally were carefully maintained to avoid what would later be discovered to be bacterial contamination, including using preservatives such as hops as well as boiling the growth medium. Hops are the female Flower cones of the hop plant ( Humulus lupulus)

Later refinements in microbiology following the work of Louis Pasteur led to more advanced methods of culturing pure strains, making modern commercial yeast possible, and turning yeast production into a major industrial endeavor. Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and The slurry yeast made by small bakers and grocery shops became cream yeast, a suspension of live yeast cells in growth medium, and then compressed yeast, the fresh cake yeast that became the standard leaven for bread bakers in much of the Westernized world during the early 20th century.

Today there are several retailers of baker's yeast; the biggest producers are Fleischmann's Yeast and Lesaffre (who also owns the popular American label Red Star Yeast). Red Star Yeast Company LLC is a joint-venture of Lesaffre Yeast Corporation and Archer Daniels Midland Company. During World War II Fleischmann's developed a granulated active dry yeast for the United States armed forces, which did not require refrigeration and had a longer shelf life and better temperature tolerance than fresh yeast; it is still the standard yeast for US military recipes. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including The company created yeast that would rise twice as fast, cutting down on baking time. Lesaffre would later create instant yeast in the 1970s, which has gained considerable use and market share at the expense of both fresh and dry yeast in their various applications.

Types of baker's yeast

Active dried yeast, a granulated form in which yeast is commercially sold.

Baker's yeast is available in a number of different forms. Though each version has certain advantages over the others, the choice of which form to use is largely a question of the requirements of the recipe at hand and the training of the cook preparing it. With occasional allowances for liquid content and temperature, the different forms of commercial yeast are generally considered interchangeable.

• Cream yeast is the closest form to the yeast slurries of the 19th century, being essentially a suspension of yeast cells in liquid, siphoned off from the growth medium. Its primary use is in industrial bakeries with special high-volume dispensing and mixing equipment, and it is not readily available to small bakeries or home cooks.
• Compressed yeast is essentially cream yeast with most of the liquid removed. It is best known in the form of cake yeast, which is essentially a soft solid, beige in color, but is also available in crumbled form for bulk usage. It is highly perishable; though formerly widely available for the consumer market, it has become less common in supermarkets in some countries due to its poor keeping properties, having been obsoleted in some such markets by active dry and instant yeast. It is still widely available for commercial use, and is somewhat more tolerant of low temperatures than other forms of commercial yeast; however, even there, instant yeast has made significant market inroads.
• Active dry yeast is the form of yeast most commonly available to noncommercial bakers, as well as the yeast of choice for situations where long travel or uncontrolled storage conditions are likely. It consists of coarse oblong granules of yeast, with live yeast cells encapsulated in a thick jacket of dry, dead cells with some growth medium. Under most conditions, active dry yeast must be proofed or rehydrated first and, despite its better keeping qualities than other forms, is generally considered more sensitive than other forms to thermal shock when actually used in recipes.
• Instant yeast appears similar to active dry yeast, but has smaller granules with substantially higher percentages of live cells. It is more perishable than active dry yeast, but also does not require rehydration, and can usually be added directly to all but the driest doughs. Instant yeast generally has a small amount of ascorbic acid added as a preservative. This article deals with the molecular aspects of ascorbic acid Some producers provide two or more forms of instant yeast in their product portfolio; for example, LeSaffre's "SAF Instant Gold" is designed specifically for doughs with high sugar contents.
• Rapid-rise yeast is a variety of yeast (usually a form of instant yeast) designed to provide greater carbon dioxide output to allow faster rising at the expense of shortened fermentation times. There is considerable debate as to the value of such a product; while most baking experts believe it reduces the flavor potential of the finished product, Cook's Illustrated magazine, among others, feels that at least for direct-rise recipes, it makes little difference. Cook’s Illustrated is a bimonthly American cooking Magazine published by Boston Common Press in Brookline Massachusetts. Rapid-rise yeast is often marketed specifically for use in bread machines.
• Flake yeast is dead yeast, sold primarily as a nutritional supplement. It has little to no leavening power.

For most commercial uses, yeast of any form is packaged in bulk (blocks or freezer bags for fresh yeast; vacuum-packed brick bags for dry or instant); however, yeast for home use is often packaged in pre-measured doses, either small squares for compressed yeast or sealed packets for dry or instant. A single dose (reckoned for the average bread recipe of between 500g and 1000g of dough) is generally about 2. 5 tsp or about 7g, though comparatively lesser amounts are used when the yeast is used in a pre-ferment. A pre-ferment (pâte fermentée also called a "sponge" or a "bread starter" is a Fermentation starter used in Bread Baking.

See also

• Sourdough
• Salt rising bread

References

• Corriher, Shirley, Cookwise. Sourdough (or more formally natural leaven or Levain) refers to the process of leavening Bread by capturing wild Yeasts Salt rising (or salt risen bread is bread in which the bacterium Clostridium perfringens is used to leaven the bread rather than Yeast or Baking soda. New York: William Morrow and Co. , 1997, ISBN 0688102298.
• Editors of Cook's Illustrated Magazine, Baking Illustrated. Brookline, MA:Boston Common Press, 2004, ISBN 0936184752.
• The King Arthur Flour Baker's Companion. Woodstock, VT: Countryman Press, 2003, ISBN 0881505811.
• Simmons, Amelia. American Cookery, Hartford, 1798. Text at Feeding America and Project Gutenberg.
• Sloat, Caroline (ed. ), Old Sturbridge Village Cookbook 2ed. . Old Saybrook: Globe Pequot Press, 1995, ISBN 1564407284.

1. ^ "The History of Bread Yeast". British Broadcasting Company. The British Broadcasting Company Ltd was a British commercial company formed on 18 October 1922 by British and American electrical companies doing business in the United Retrieved December 24, 2006. Events 563 - The Byzantine church Hagia Sophia in Constantinople is dedicated for the second time after being destroyed by Earthquakes Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar.