In cooking , proofing (also called proving ) is a step in the preparation of yeast bread and other baked goods in which the dough is allowed to rest and rise a final time before baking . During this rest period, yeast ferments the dough and produces gases, thereby leavening the dough.
96-413: In contrast, proofing or blooming yeast (as opposed to proofing the dough) may refer to the process of first suspending yeast in warm water, a necessary hydration step when baking with active dry yeast . Proofing can also refer to the process of testing the viability of dry yeast by suspending it in warm water with carbohydrates (sugars). If the yeast is still alive, it will feed on the sugar and produce
192-446: A leavening agent which causes the bread to rise (expand and become lighter and softer) by converting the fermentable sugars present in the dough into carbon dioxide and ethanol . Baker's yeast is of the species Saccharomyces cerevisiae , and is the same species (but a different strain ) as the kind commonly used in alcoholic fermentation, which is called brewer's yeast or the deactivated form nutritional yeast . Baker's yeast
288-458: A bread with poor structure. Length of rest periods, including proofing, can be determined by time at specific temperatures or by characteristics. Often the "poke method" is used to determine if a dough has risen long enough. If the dough, when poked, springs back immediately it is underproofed and needs more time. Some breads are considered fully proofed if the indent left by the poke springs back slowly, while others are considered fully proofed when
384-559: A cloth liner, generally made of linen, to prevent dough from sticking to the sides of the basket. Bannetons become more non-stick with use as a small amount of flour accumulates in them. These baskets are used both to provide the loaf with shape and to wick moisture from the crust . Bannetons come in round or oblong shapes. Alternatively, a couche (pronounced koosh ), bakery couche, or proofing cloth, can be used on which to proof dough. They are used for longer loaves, such as baguettes . Couches are typically made of linen . Flour collects in
480-672: A container of diethyl ether , which then boiled , absorbing heat from the surrounding air. The experiment even created a small amount of ice, but had no practical application at that time. In 1805, American inventor Oliver Evans described a closed vapor-compression refrigeration cycle for the production of ice by ether under vacuum. In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures, and in 1834, an American expatriate in Great Britain, Jacob Perkins , built
576-415: A dispenser in the door. Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest are Peltier-type refrigerators designed to chill beverages. A large domestic refrigerator stands as tall as a person and may be about one metre (3 ft 3 in) wide with a capacity of 0.6 m (21 cu ft). Refrigerators and freezers may be free standing, or built into
672-475: A dough retarder, see below. Commercial bakers typically use large, temperature- and humidity-controlled proofers, whereas home bakers employ a variety of methods to create a warm, humid environment for dough rising. Examples include a home oven with a bowl of water and the pilot light on, a box with a bowl of hot water in it (the water is replaced periodically to maintain warmth), or a counter top proofer (an electric appliance) designed for home use. A dough retarder
768-579: A dozen of his systems were in operation. The first gas absorption refrigeration system (compressor-less and powered by a heat-source) was developed by Edward Toussaint of France in 1859 and patented in 1860. It used gaseous ammonia dissolved in water ("aqua ammonia"). Carl von Linde , an engineering professor at the Technological University Munich in Germany, patented an improved method of liquefying gases in 1876, creating
864-449: A frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers). Refrigerators and freezers may be free-standing, or built into a kitchen's cabinet. Three distinct classes of refrigerator are common: Other specialized cooling mechanisms may be used for cooling, but have not been applied to domestic or commercial refrigerators. In
960-454: A house without air-conditioning (space heating and/or cooling) refrigerators consume more energy than any other home device. In the early 1990s a competition was held among the major US manufacturers to encourage energy efficiency. Current US models that are Energy Star qualified use 50% less energy than the average 1974 model used. The most energy-efficient unit made in the US consumes about half
1056-449: A kilowatt-hour per day (equivalent to 20 W continuously). But even ordinary units are reasonably efficient; some smaller units use less than 0.2 kWh per day (equivalent to 8 W continuously). Larger units, especially those with large freezers and icemakers, may use as much as 4 kW·h per day (equivalent to 170 W continuously). The European Union uses a letter-based mandatory energy efficiency rating label , with A being
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#17327936415451152-431: A kitchen. The refrigerator allows the modern household to keep food fresh for longer than before. Freezers allow people to buy perishable food in bulk and eat it at leisure, and make bulk purchases . Ancient origins Ancient Iranians were among the first to invent a form of cooler utilizing the principles of evaporative cooling and radiative cooling called yakhchāls . These complexes used subterranean storage spaces,
1248-614: A large industrial ammonia refrigerator which was powered by electric compressors (together with the Esslingen Machine Works). Its electric compressors were manufactured by the Ganz Works . At the 1896 Millennium Exhibition, Röck and the Esslingen Machine Works presented a 6-tonne capacity artificial ice producing plant. In 1906, the first large Hungarian cold store (with a capacity of 3,000 tonnes,
1344-526: A large thickly insulated above-ground domed structure, and outfitted with badgirs (wind-catchers) and series of qanats (aqueducts). Pre-electric refrigeration In modern times, before the invention of the modern electric refrigerator, icehouses and iceboxes were used to provide cool storage for most of the year. Placed near freshwater lakes or packed with snow and ice during the winter, they were once very common. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow
1440-399: A liquid nitrogen backup. Alternatives to the vapor-compression cycle not in current mass production include: Many modern refrigerator/freezers have the freezer on top and the refrigerator on the bottom. Most refrigerator-freezers—except for manual defrost models or cheaper units—use what appears to be two thermostats. Only the refrigerator compartment is properly temperature controlled. When
1536-540: A luxury item, became commonplace. Freezer units are used in households as well as in industry and commerce. Commercial refrigerator and freezer units were in use for almost 40 years prior to the common home models. The freezer-over-refrigerator style had been the basic style since the 1940s, until modern, side-by-side refrigerators broke the trend. A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. Newer refrigerators may include automatic defrosting , chilled water, and ice from
1632-449: A luxury item, became commonplace. In 1955 the domestic deep freezer, which was cold enough to allow the owners to freeze fresh food themselves rather than buying food already frozen with Clarence Birdseye's process, went on sale. There are walk in freezers, as the name implies, they allow for one to walk into the freezer. Safety regulations requires an emergency releases and employers should check to ensure no one will trapped inside when
1728-458: A part of the dough ("pre-ferment") before the final mixing, with the entire dough during bulk fermentation, or in the final fermentation stages after shaping. To ensure consistent results and maintain baking schedules, specialized tools are used to manipulate the speed and qualities of fermentation. A dough proofer is a warming chamber used in baking that encourages fermentation of dough by yeast through warm temperatures and controlled humidity. It
1824-400: A phenomenon known as auto-refrigeration . This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps
1920-554: A range of sizes. Among the smallest is a 4-litre (0.14 cu ft) Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about 1 metre (3.3 ft) wide with a capacity of 600 litres (21 cu ft). Some models for small households fit under kitchen work surfaces, usually about 86 centimetres (34 in) high. Refrigerators may be combined with freezers, either stacked with refrigerator or freezer above, below, or side by side. A refrigerator without
2016-421: A short rest period during which the cells first accommodate to the environment and then begin to grow, a layer of foam is developed by the action of the yeast, a sign of primary fermentation and live yeast. Typically 60 ml ( 1 ⁄ 4 cup) water at 40–45 °C (105–115 °F) and 2 g ( 1 ⁄ 2 teaspoon) of sugar are used, or expressed differently, a sugar weight of about 3.5% of
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#17327936415452112-569: A shortage of yeast for making bread, so the Vienna Process was developed in 1846. While the innovation is often popularly credited for using steam in baking ovens, leading to a different crust characteristic, it is notable for including procedures for high milling of grains (see Vienna grits ), cracking them incrementally instead of mashing them with one pass; as well as better processes for growing and harvesting top-fermenting yeasts, known as press-yeast. Refinements in microbiology following
2208-423: A similar gas, as a refrigerant, with its condenser kept at around −40 °C by a second stage which uses a more conventional refrigerant. For much lower temperatures, laboratories usually purchase liquid nitrogen (−196 °C [−320.8 °F]), kept in a Dewar flask , into which the samples are suspended. Cryogenic chest freezers can achieve temperatures of down to −150 °C (−238 °F), and may include
2304-519: A single mixing period. During bulk fermentation straight-dough recipes may instruct a baker to "punch down" or "deflate" the dough, while artisan bakers will use terms like "stretching", "folding", and "degassing", meaning to expel gas from the carbon dioxide bubbles that have formed. Sponge doughs will need multiple mixing periods. Overproofing occurs when a fermenting dough has rested too long. Its bubbles have grown so large that they have popped and tunneled, and dough baked at this point would result in
2400-463: A slurry with a composition similar to beer wort , usually including malted barley and wheat flour. Such cultures (sometimes referred to in old American cookery as "emptins", from their origins as the dregs of beer or cider fermentation) became the ancestors of modern baker's yeast, as, in general, they were carefully maintained to avoid what was later discovered to be bacterial contamination, including using preservatives such as hops as well as boiling
2496-571: 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. 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
2592-460: A unit that was mounted on top of an ice box. His first device, produced over the next few years in several hundred units, was called DOMELRE . In 1914, engineer Nathaniel B. Wales of Detroit, Michigan, introduced an idea for a practical electric refrigeration unit, which later became the basis for the Kelvinator . A self-contained refrigerator, with a compressor on the bottom of the cabinet
2688-417: A visible layer of foam on the surface of the water mixture. Fermentation rest periods are not always explicitly named, and can appear in recipes as "Allow dough to rise." When they are named, terms include "bulk fermentation", "first rise", "second rise", "final proof" and "shaped proof". The process of making yeast-leavened bread involves a series of alternating work and rest periods. Work periods occur when
2784-477: Is a refrigerator used to control the fermentation of yeast when proofing dough. Lowering the temperature of the dough produces a slower, longer rise with more varied fermentation products, resulting in more complex flavors. In sourdough bread-making, cold decreases the activity of wild yeast relative to the Lactobacilli , which produce flavoring products such as lactic acid and acetic acid . Sourdough that
2880-424: Is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so that its inside is cooled to a temperature below the room temperature. Refrigeration is an essential food storage technique around the world. The low temperature reduces the reproduction rate of bacteria , so
2976-415: Is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors. The word "refrigeratory" was used at least as early as the 17th century. Artificial refrigeration The history of artificial refrigeration began when Scottish professor William Cullen designed a small refrigerating machine in 1755. Cullen used a pump to create a partial vacuum over
Proofing (baking technique) - Misplaced Pages Continue
3072-561: Is a type of basket used to provide structure for shaped loaves of bread during proofing. Banneton baskets are also known as brotform or proofing baskets. It is normally used for doughs that are too soft or wet to maintain their shape while rising. Proofing baskets are distinct from loaf pans in that the bread is normally removed from these baskets before baking. Conventionally, these baskets are made out of rattan , but some modern proofing baskets are made out of cane , spruce pulp, terracotta , or polypropylene . A banneton will sometimes have
3168-427: Is about 2.5 tsp (~12 mL) or about 7 g ( 1 ⁄ 4 oz), though comparatively lesser amounts are used when the yeast is used in a pre-ferment . In general, a yeast flavor in the baked bread is not noticeable when the bakers' percent of added yeast is less than 2.5%. Notable commercial brands of baker's yeast include Lesaffre 's SAF red and SAF gold, Fleischmann's , and Red Star Yeast . Because it
3264-420: Is also a single-cell microorganism found on and around the human body. The use of steamed or boiled potatoes, water from potato boiling, or sugar in a bread dough provides food for the growth of yeasts; however, too much sugar will dehydrate them. Yeast growth is inhibited by both salt and sugar, but more so by salt than sugar. Some sources say fats, such as butter and eggs, slow down yeast growth; others say
3360-446: Is also called a proofing box, proofing oven, or proofing cabinet. The warm temperatures increase the activity of the yeast, resulting in increased carbon dioxide production and a higher, faster rise. Dough is typically allowed to rise in the proofer before baking, but can also be used for the first rise, or bulk fermentation. Desired proofer temperatures can range from 20 to 45 °C (70 to 115 °F); cooler temperatures are achieved in
3456-519: Is available in a number of different forms, the main differences being the moisture contents. 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. Dry yeast forms are good choices for longer-term storage, often lasting more than a year at room temperatures without significant loss of viability. In general, with occasional allowances for liquid content and temperature,
3552-453: Is credited to Raymond Calvel , who recommended it as a way to reduce kneading time and thereby improve the flavor and color of bread. ' Proofing the yeast' is a hydration process that occurs when dry yeast is mixed with warm water and allowed to rest for a short time. The minimum weight of water required may be calculated: yeast weight x 4 = water weight . Yeast viability can be tested by mixing yeast in warm water and sugar, and following
3648-410: Is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant,
3744-404: Is not acceptable. They can be totally silent (if a fan for air circulation is not fitted) but are less energy-efficient than other methods. "Ultra-cold" or " ultra-low temperature (ULT) " (typically −80 or −86 °C [−112 or −123 °F]) freezers, as used for storing biological samples, also generally employ two stages of cooling, but in cascade . The lower temperature stage uses methane , or
3840-401: 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. For active dry and instant yeast, in general a single dose (reckoned for the average bread recipe of between 500 g and 1000 g of dough)
3936-483: Is readily available and easy to culture, baker's yeast has long been used in chemical, biological, and genetic research as a model organism . Saccharomyces cerevisiae is a facultative anaerobe and undergoes aerobic fermentation in the presences of oxygen and sugars. In 1996, after six years of work, S. cerevisiae became the first eukaryote to have its entire genome sequenced . It has over 12 million base pairs and around 6000 genes . Since then, it has remained in
Proofing (baking technique) - Misplaced Pages Continue
4032-434: Is retarded before baking can result in a more sour loaf. To prevent the dough from drying, air flow in the dough retarder is kept to a minimum. Home bakers may use cloth or other cover for dough that is kept for a longer period in the refrigerator. Commercial bakers often retard dough at approximately 10 °C (50 °F), while home bakers typically use refrigerators set at about 4 °C (40 °F) or below. A banneton
4128-423: Is still blown from the freezer. Newer refrigerators may include: These older freezer compartments were the main cooling body of the refrigerator, and only maintained a temperature of around −6 °C (21 °F), which is suitable for keeping food for a week. Later advances included automatic ice units and self compartmentalized freezing units. Domestic refrigerators and freezers for food storage are made in
4224-448: Is still found in many old systems. Refrigeration, continually operated, typically consumes up to 50% of the energy used by a supermarket. Doors, made of glass to allow inspection of contents, improve efficiency significantly over open display cases, which use 1.3 times the energy. In 1913, the first electric refrigerators for home and domestic use were invented and produced by Fred W. Wolf of Fort Wayne, Indiana, with models consisting of
4320-518: Is still the standard yeast for US military recipes. The company created yeast that would rise twice as fast, cutting down on baking time. In 1973, Lesaffre created instant yeast (also called "quick rise" or "fast acting" yeast), which has gained considerable use and market share at the expense of both fresh and active dry yeast in their various applications. Instant yeast differs from active dry yeast in several ways: Instant yeast rises faster than active dry yeast; instant yeast can be directly added to
4416-518: Is the highest qualification, for those refrigerators that are at least 30% more efficient than Federal standards. About 82% of the Energy Star qualified refrigerators are Tier 1, with 13% qualifying as Tier 2, and just 5% at Tier 3. Besides the standard style of compressor refrigeration used in ordinary household refrigerators and freezers, there are technologies such as absorption and magnetic refrigeration . Although these designs generally use
4512-436: Is the specific term for allowing dough to rise after it has been shaped and before it is baked. Some breads begin mixing with an autolyse . This refers to a period of rest after the initial mixing of flour and water, a rest period that occurs sequentially before the addition of yeast, salt and other ingredients. This rest period allows for better absorption of water and helps the gluten and starches to align. The autolyse
4608-546: The Royal Institute of Technology in Stockholm. It became a worldwide success and was commercialized by Electrolux . Other pioneers included Charles Tellier , David Boyle, and Raoul Pictet . Carl von Linde was the first to patent and make a practical and compact refrigerator. These home units usually required the installation of the mechanical parts, motor and compressor, in the basement or an adjacent room while
4704-423: The icebox , which had been a common household appliance for almost a century and a half. The United States Food and Drug Administration recommends that the refrigerator be kept at or below 4 °C (40 °F) and that the freezer be regulated at −18 °C (0 °F). The first cooling systems for food involved ice. Artificial refrigeration began in the mid-1750s, and developed in the early 1800s. In 1834,
4800-512: The 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940s; the term for the unit, popular at the time, was deep freeze . These devices, or appliances , did not go into mass production for use in the home until after World War II. The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. More efficient refrigerators were developed in
4896-466: The 1920s; up to this time freezing was not an auxiliary function of the modern refrigerator. The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927, so-called, by the public, because of its resemblance to the gun turret on the ironclad warship USS Monitor of the 1860s. The compressor assembly, which emitted a great deal of heat,
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#17327936415454992-567: The 1970s and 1980s, even though environmental issues led to the banning of very effective (Freon) refrigerants. Early refrigerator models (from 1916) had a cold compartment for ice cube trays. From the late 1920s fresh vegetables were successfully processed through freezing by the Postum Company (the forerunner of General Foods ), which had acquired the technology when it bought the rights to Clarence Birdseye 's successful fresh freezing methods. The majority of refrigerators were white in
5088-685: The 1980s, black became fashionable. In the late 1990s stainless steel came into vogue. Since 1961 the Color Marketing Group has attempted to coordinate the colors of appliances and other consumer goods. Freezer units are used in households and in industry and commerce. Food stored at or below −18 °C (0 °F) is safe indefinitely. Most household freezers maintain temperatures from −23 to −18 °C (−9 to 0 °F), although some freezer-only units can achieve −34 °C (−29 °F) and lower. Refrigerator freezers generally do not achieve lower than −23 °C (−9 °F), since
5184-419: The United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon-12 (R-12) were introduced. However, R-12 proved to be damaging to the ozone layer , causing governments to issue a ban on its use in new refrigerators and air-conditioning systems in 1994. The less harmful replacement for R-12, R-134a (tetrafluoroethane), has been in common use since 1990, but R-12
5280-472: The beer fermentation process can also be used in bread making. Without an 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. 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
5376-613: The box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle. Modern domestic refrigerators are extremely reliable because motor and compressor are integrated within a welded container, "sealed unit", with greatly reduced likelihood of leakage or contamination. By comparison, externally-coupled refrigeration compressors, such as those in automobile air conditioning, inevitably leak fluid and lubricant past
5472-525: The cold box was located in the kitchen. There was a 1922 model that consisted of a wooden cold box, water-cooled compressor, an ice cube tray and a 0.25-cubic-metre (9 cu ft) compartment, and cost $ 714. (A 1922 Model-T Ford cost about $ 476.) By 1923, Kelvinator held 80 percent of the market for electric refrigerators. Also in 1923 Frigidaire introduced the first self-contained unit. About this same time porcelain-covered metal cabinets began to appear. Ice cube trays were introduced more and more during
5568-409: The compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes that make up the condenser ; the coils or tubes are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant
5664-564: The compressor motor in a typical refrigerator. A fan or pump might be the only mechanical moving parts; reliance on convection is considered impractical. Other uses of an absorption refrigerator (or "chiller") include large systems used in office buildings or complexes such as hospitals and universities. These large systems are used to chill a brine solution that is circulated through the building. The Peltier effect uses electricity to pump heat directly; refrigerators employing this system are sometimes used for camping, or in situations where noise
5760-434: The different forms of commercial yeast are considered interchangeable. Instant and active dry yeast are essentially the same ingredient, just in slightly different forms and applications. Consumers should keep sealed packets of both yeast types at room temperature and store partially used packets in an airtight container in the refrigerator. The main differences between the two are: For most commercial uses, yeast of any form
5856-429: The dough is manipulated by the baker. Some work periods are called mixing , kneading , and folding , as well as division , shaping , and panning . Work periods are typically followed by rest periods, which occur when dough is allowed to sit undisturbed. Particular rest periods include, but are not limited to, autolyse , bulk fermentation and proofing . Proofing , also sometimes called final fermentation ,
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#17327936415455952-677: The dry ingredients, whereas active dry yeast should be mixed with liquid (water, milk or beer) and proofed before mixing; instant yeast has a lower moisture content; and instant yeast is formed of smaller granules. Modern baker's yeast is the species Saccharomyces cerevisiae . One of its properties is that it is not inhibited by propionates , which are commonly added to baked goods like bread dough to inhibit mold development and bacterial growth. Conversely, sorbates do inhibit yeast fermentation activity, so are not added directly to yeast-leavened dough but may be sprayed onto finished products or even incorporated into packing materials. Baker's yeast
6048-433: The earliest forms of leavening were likely very similar to modern sourdough; the leavening action of yeast would have been discovered from its action on flatbread doughs and would have been either cultivated separately or transferred from batch to batch by means of previously mixed ("old") dough. Also, the development of leavened bread seems to have developed in close proximity to the development of beer brewing, and barm from
6144-446: The early 1950s, but between the mid-1950s and the present, manufacturers and designers have added color. Pastel colors, such as pink and turquoise, gained popularity in the late 1950s and early 1960s. Certain versions also had brushed chrome plating, which is akin to a stainless steel appearance. During the latter part of the 1960s and the early 1970s, earth tone colors were popular, including Harvest Gold , Avocado Green and almond. In
6240-412: The effect of fat on dough remains unclear, presenting evidence that small amounts of fat are beneficial for baked bread volume. Saccharomyces exiguus (also known as S. minor ) is a wild yeast found on plants, grains, and fruits that is occasionally used for baking; however, in general, it is not used in a pure form but comes from being propagated in a sourdough starter . It is not known when yeast
6336-410: The end of the nineteenth century, baker's yeast has been produced by companies that specialize in its production. The main ingredients for industrial production are yeast cultures, sugar from cane and sugar beet ; but a number of minerals, nitrogen and vitamins are also needed. Fermentation happens in several phases, which vary depending on the manufacturer: The yeast grows from hundreds kg in
6432-441: The first reliable and efficient compressed-ammonia refrigerator. His new process made possible the use of gases such as ammonia (NH 3 ), sulfur dioxide (SO 2 ) and methyl chloride (CH 3 Cl) as refrigerants, which were widely used for that purpose until the late 1920s despite safety concerns. In 1895 he discovered the refrigeration cycle . In 1894, Hungarian inventor and industrialist István Röck started to manufacture
6528-531: The first working vapor-compression refrigeration , using the same technology seen in air conditioners , system was built. The first commercial ice-making machine was invented in 1854. In 1913, refrigerators for home use were invented. In 1923 Frigidaire introduced the first self-contained unit. The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s. Home freezers as separate compartments (larger than necessary just for ice cubes) were introduced in 1940. Frozen foods , previously
6624-440: The first working vapor-compression refrigeration system. It was a closed-cycle device that could operate continuously. A similar attempt was made in 1842, by American physician, John Gorrie , who built a working prototype, but it was a commercial failure. American engineer Alexander Twining took out a British patent in 1850 for a vapor compression system that used ether. The first practical vapor compression refrigeration system
6720-626: The forefront of genetic research. For example, most of our knowledge of the cell division cycle was worked out from experiments with yeast. Baker's yeast contains enzymes that can reduce a carbonyl group into a hydroxyl group in fairly high yield, thus making it useful for biotransformations in organic syntheses . It is known to reduce organometallic carbonyl compounds in very high yield. The baking industry relies on industrial production of its ingredients, including baking yeasts. Much effort has been put into developing and marketing yeasts that will perform reliably in mass production. Since
6816-415: The freezer temperature will have no effect on the refrigerator temperature. The freezer control may also be adjusted to compensate for any refrigerator adjustment. This means the refrigerator may become too warm. However, because only enough air is diverted to the refrigerator compartment, the freezer usually re-acquires the set temperature quickly, unless the door is opened. When a door is opened, either in
6912-428: The gluten structure. Retarding may occur at any time during fermentation and is accomplished by placing the dough into a dough retarder, refrigerator, or other cold environment to slow the activity of the yeast. The retarding stage is often used in sourdough bread recipes to allow the bread to develop its characteristic flavor. A cold fermentation stage is sometimes used to develop flavor in other artisan breads, with
7008-402: The grain to maltose . The baker's yeast enzyme maltase converts maltose into glucose, invertase converts any added sucrose to glucose and fructose , and zymase converts glucose and fructose to carbon dioxide gas which makes the dough rise, and alcohol which gives the baked bread flavor. Sourdough starters also produce lactic and acetic acids , further contributing to flavor. When
7104-465: The growth medium. In the 19th century, bread bakers obtained their yeast from beer brewers, and this led to sweet-fermented breads such as the Imperial " Kaiser-Semmel " roll, which in general lacked the sourness created by the acidification typical of Lactobacillus . However, beer brewers slowly switched from top-fermenting to bottom-fermenting yeast ( Saccharomyces pastorianus ) and this created
7200-421: The indent remains and does not spring back. A bread that is properly proofed will balance gas production with the ability of the bread's gluten structure to contain it, and will exhibit good oven spring when baked. A bread that is under- or overproofed will have less oven spring and be denser. An overproofed bread may even collapse in the oven as the volume of gas produced by the yeast can no longer be contained by
7296-423: The intermediate and stock fermentor to tens of thousands kg in the trade fermentor, where most yeast is produced. The earlier stages produce more ethanol and other alcohols, while in the final stages ethanol production is suppressed up to 95% by controlling the amount of oxygen and sugar, in order to increase the yeast production instead. The industry is highly concentrated, with five companies holding up to 80% of
7392-872: The largest in Europe) opened in Tóth Kálmán Street, Budapest, the machine was manufactured by the Ganz Works . Until nationalisation after the Second World War, large-scale industrial refrigerator production in Hungary was in the hands of Röck and Ganz Works. Commercial refrigerator and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models. They used gas systems such as ammonia (R-717) or sulfur dioxide (R-764), which occasionally leaked, making them unsafe for home use. Practical household refrigerators were introduced in 1915 and gained wider acceptance in
7488-421: The lid or door on top, sacrificing convenience for efficiency and partial immunity to power outages. Many modern upright freezers come with an ice dispenser built into their door. Some upscale models include thermostat displays and controls. Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940. Frozen foods, previously
7584-399: The more humid refrigerator air is mixed with the dry freezer air. Multiple manufacturers offer dual compressor models. These models have separate freezer and refrigerator compartments that operate independently of each other, sometimes mounted within a single cabinet. Each has its own separate compressor, condenser and evaporator coils, insulation, thermostat, and door. A hybrid between
7680-625: The most efficient, instead of the Energy Star. For US refrigerators, the Consortium on Energy Efficiency (CEE) further differentiates between Energy Star qualified refrigerators. Tier 1 refrigerators are those that are 20% to 24.9% more efficient than the Federal minimum standards set by the National Appliance Energy Conservation Act (NAECA). Tier 2 are those that are 25% to 29.9% more efficient. Tier 3
7776-412: The refrigerator gets too warm, the thermostat starts the cooling process and a fan circulates the air around the freezer. During this time, the refrigerator also gets colder. The freezer control knob only controls the amount of air that flows into the refrigerator via a damper system. Changing the refrigerator temperature will inadvertently change the freezer temperature in the opposite direction. Changing
7872-412: The refrigerator lowers the rate of spoilage . A refrigerator maintains a temperature a few degrees above the freezing point of water. The optimal temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F). A freezer is a specialized refrigerator, or portion of a refrigerator, that maintains its contents’ temperature below the freezing point of water. The refrigerator replaced
7968-420: The refrigerator or the freezer, the fan in some units stops immediately to prevent excessive frost build up on the freezer's evaporator coil, because this coil is cooling two areas. When the freezer reaches temperature, the unit cycles off, no matter what the refrigerator temperature is. Modern computerized refrigerators do not use the damper system. The computer manages fan speed for both compartments, although air
8064-422: The same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers may be either upright, resembling a refrigerator, or chest freezers , wider than tall with
8160-454: The shaft seals. This leads to a requirement for periodic recharging and, if ignored, possible compressor failure. Refrigerators with two compartments need special design to control the cooling of refrigerator or freezer compartments. Typically, the compressors and condenser coils are mounted at the top of the cabinet, with a single fan to cool them both. This arrangement has a few downsides: each compartment cannot be controlled independently and
8256-475: The two designs is using a separate fan for each compartment, the Dual Fan approach. Doing so allows for separate control and airflow on a single compressor system. An absorption refrigerator works differently from a compressor refrigerator, using a source of heat , such as combustion of liquefied petroleum gas , solar thermal energy or an electric heating element. These heat sources are much quieter than
8352-404: The unit gets locked as hypothermia is possible if one is in freezer for longer periods of time. A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly below the temperature of the refrigerator interior. The vapor is compressed and exits
8448-425: The water's weight. While this sugar may be sucrose or table sugar, instead it may be glucose or maltose . Fermentation typically begins when viable baker's yeast or a starter culture is added to flour and water. Enzymes in the flour and yeast create sugars, which are consumed by the yeast, which in turn produce carbon dioxide and alcohol. Specifically, the grain enzyme diastase begins to convert starch in
8544-482: The weave creating a less-sticky surface. The couche is dusted lightly with flour, then shaped doughs are laid on top of it and folds are placed to separate and support them while proofing. Breads such as sandwich loaves and brioche are normally proofed in the bread pan in which they will be baked. Baker%27s yeast#Types of baker's yeast Baker yeast is the common name for the strains of yeast commonly used in baking bread and other bakery products, serving as
8640-470: The work of Louis Pasteur led to more advanced methods of culturing pure strains. In 1879, Great Britain introduced specialized growing vats for the production of S. cerevisiae , and in the United States around the turn of the century centrifuges were used for concentrating the yeast, making modern commercial yeast possible, and turning yeast production into a major industrial endeavor. The slurry yeast made by small bakers and grocery shops became cream yeast,
8736-562: The worldwide market for dry yeast as of 2006. While dry yeast is exported over long distances and mostly sold in the developing countries, industrial customers often prefer to supply fresh yeast from local facilities, with a single wholesaler having up to 90% of the liquid yeast market in the UK in 2006. In the US companies like Lesaffre Group , AB Vista, GB Plange and AB Mauri produced hundreds of thousands of metric tons of yeast in 2012. Refrigerator A refrigerator , commonly fridge ,
8832-442: The yeast cells die, they release high quantities of a protease which snip protein strands, and in large die-offs result in soft, sticky dough, less baked volume, and a coarse crumb, but in smaller die offs, increase dough extensibility and baked volume. Different bread varieties will have different process requirements. These are generally classified as either straight or sponge dough processes. Straight doughs will require only
8928-556: Was built by James Harrison , a Scottish Australian. His 1856 patent was for a vapor compression system using ether, alcohol or ammonia. He built a mechanical ice-making machine in 1851 on the banks of the Barwon River at Rocky Point in Geelong , Victoria , and his first commercial ice-making machine followed in 1854. Harrison also introduced commercial vapor-compression refrigeration to breweries and meat packing houses, and by 1861,
9024-408: Was first used to bake bread; the earliest definite records come from Ancient Egypt. 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 tastier than the previous hard flatbreads . It is generally assumed that
9120-509: Was invented by Alfred Mellowes in 1916. Mellowes produced this refrigerator commercially but was bought out by William C. Durant in 1918, who started the Frigidaire company to mass-produce refrigerators. In 1918, Kelvinator company introduced the first refrigerator with any type of automatic control. The absorption refrigerator was invented by Baltzar von Platen and Carl Munters from Sweden in 1922, while they were still students at
9216-409: Was placed above the cabinet, and enclosed by a decorative ring. Over a million units were produced. As the refrigerating medium, these refrigerators used either sulfur dioxide , which is corrosive to the eyes and may cause loss of vision, painful skin burns and lesions, or methyl formate , which is highly flammable, harmful to the eyes, and toxic if inhaled or ingested. The introduction of Freon in
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