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醣化.煮花.發酵 達人教戰DIY釀酒術! 地球黃金線 20160902 (2/4)
享受微醺時光 席捲全球的精釀釀酒風潮! 地球黃金線 20160902 (完整版)
The process of brewing beer
Hot water tank
Malting is the process where barley grain is made ready for brewing. [52] Malting is broken down into three steps in order to help to release the starches in the barley. [53] First, during steeping, the grain is added to a vat with water and allowed to soak for approximately 40 hours. [54] During germination, the grain is spread out on the floor of the germination room for around 5 days. [54] The final part of malting is kilning when the malt goes through a very high temperature drying in a kiln; with gradual temperature increase over several hours. [55]
When kilning is complete, the grains are now termed malt, and they will be milled or crushed to break apart the kernels and expose the cotyledon, which contains the majority of the carbohydrates and sugars; this makes it easier to extract the sugars during mashing. [56] Milling also separates the seed from the husk. Care must be taken when milling to ensure that the starch reserves are sufficiently milled without damaging the husk and providing coarse enough grits that a good filter bed can be formed during lautering. Grains are typically dry-milled with roller mills or hammer mills. Hammer mills, which produce a very fine mash, are often used when mash filters are going to be employed in the lautering process because the grain does not have to form its own filter bed. In modern plants, the grain is often conditioned with water before it is milled to make the husk more pliable, thus reducing breakage and improving lauter speed.
Mashing converts the starches released during the malting stage into sugars that can be fermented. The milled grain is mixed with hot water in a large vessel known as a mash tun. In this vessel, the grain and water are mixed together to create a cereal mash. During the mash, naturally occurring enzymes present in the malt convert the starches (long chain carbohydrates) in the grain into smaller molecules or simple sugars (mono-, di-, and tri-saccharides). This "conversion" is called saccharificationwhich occurs between the temperatures 140 - 158 degrees F [57]. The result of the mashing process is a sugar-rich liquid or "wort", which is then strained through the bottom of the mash tun in a process known as lautering. Prior to lautering, the mash temperature may be raised to about 75–78 °C (167–172 °F) (known as a mashout) to free up more starch and reduce mash viscosity. Additional water may be sprinkled on the grains to extract additional sugars (a process known as sparging). [58]
The wort is moved into a large tank known as a "copper" or kettle where it is boiled with hops and sometimes other ingredients such as herbs or sugars. This stage is where many chemical reactions take place, and where important decisions about the flavour, colour, and aroma of the beer are made. [59] The boiling process serves to terminate enzymatic processes, precipitate proteins, isomerize hop resins, and concentrate and sterilize the wort. Hops add flavour, aroma and bitterness to the beer. At the end of the boil, the hopped wort settles to clarify in a vessel called a "whirlpool", where the more solid particles in the wort are separated out. [60]
After the whirlpool, the wort is drawn away from the compacted hop trub, and rapidly cooled via a heat exchanger to a temperature where yeast can be added. A variety of heat exchanger designs are used in breweries, with the most common a plate-style. Water or glycol run in channels in the opposite direction of the wort, causing a rapid drop in temperature. It is very important to quickly cool the wort to a level where yeast can be added safely as yeast is unable to grow in very high temperatures, and will start to die in temperatures above 60 °C (140 °F). [56][61] After the wort goes through the heat exchanger, the cooled wort goes into a fermentation tank. A type of yeast is selected and added, or "pitched", to the fermentation tank. [59]When the yeast is added to the wort, the fermenting process begins, where the sugars turn into alcohol, carbon dioxide and other components. When the fermentation is complete the brewer may rack the beer into a new tank, called a conditioning tank. [58] Conditioning of the beer is the process in which the beer ages, the flavour becomes smoother, and flavours that are unwanted dissipate. [60] After conditioning for a week to several months, the beer may be filtered and force carbonated for bottling, [62] or fined in the cask. [63]
Mashing
Lautering
Lautering is the separation of the wort (the liquid containing the sugar extracted during mashing) from the grains.
Boiling
After mashing, the beer wort is boiled with hops (and other flavourings if used) in a large tank known as a "copper" or brew kettle – though historically the mash vessel was used and is still in some small breweries.
Brew kettle or copper
Brew kettles at Brasserie La Choulette in France
Copper is the traditional material for the boiling vessel, because copper transfers heat quickly and evenly, and because the bubbles produced during boiling, and which would act as an insulator against the heat, do not cling to the surface of copper, so the wort is heated in a consistent manner.
Whirlpool
At the end of the boil, solid particles in the hopped wort are separated out, usually in a vessel called a "whirlpool" or "settling tank".
Hopback
A hopback is a traditional additional chamber that acts as a sieve or filter by using whole hops to clear debris (or " trub") from the unfermented (or "green") wort, ] as the whirlpool does, and also to increase hop aroma in the finished beer. [8
Wort cooling
After the whirlpool, the wort must be brought down to fermentation temperatures 20–26 °C (68–79 °F) before yeast is added. In modern breweries this is achieved through a plate heat exchanger. A plate heat exchanger has many ridged plates, which form two separate paths. The wort is pumped into the heat exchanger, and goes through every other gap between the plates. The cooling medium, usually water, goes through the other gaps. The ridges in the plates ensure turbulent flow. A good heat exchanger can drop 95 °C (203 °F) wort to 20 °C (68 °F) while warming the cooling medium from about 10 °C (50 °F) to 80 °C (176 °F). The last few plates often use a cooling medium which can be cooled to below the freezing point, which allows a finer control over the wort-out temperature, and also enables cooling to around 10 °C (50 °F). After cooling, oxygen is often dissolved into the wort to revitalize the yeast and aid its reproduction.
Fermenting
Modern closed fermentation vessels
Fermentation takes place in fermentation vessels which come in various forms, from enormous cylindroconical vessels, through open stone vessels, to wooden vats. After the wort is cooled and aerated – usually with sterile air – yeast is added to it, and it begins to ferment. It is during this stage that sugars won from the malt are converted into alcohol and carbon dioxide, and the product can be called beer for the first time.
Fermentation methods
Open vessel showing fermentation taking place
There are three main fermentation methods, warm, cool and wild or spontaneous. Fermentation may take place in open or closed vessels. There may be a secondary fermentation which can take place in the brewery, in the cask or in the bottle.
Brewing yeasts are traditionally classed as "top-cropping" (or "top-fermenting") and "bottom-cropping" (or "bottom-fermenting"). Yeast were termed top or bottom cropping, because in traditional brewing yeast was collected from the top or bottom of the fermenting wort to be reused for the next brew. This terminology is somewhat inappropriate in the modern era; after the widespread application of brewing mycology it was discovered that the two separate collecting methods involved two different yeast species that favoured different temperature regimes, namely Saccharomyces cerevisiae in top-cropping at warmer temperatures and Saccharomyces pastorianus in bottom-cropping at cooler temperatures. As brewing methods changed in the 20th century, cylindro-conical fermenting vessels became the norm and the collection of yeast for both Saccharomycesspecies is done from the bottom of the fermenter. Thus the method of collection no longer implies a species association. There are a few remaining breweries who collect yeast in the top-cropping method, such as Samuel Smiths brewery in Yorkshire, Marstons in Staffordshire and several German hefeweizen producers.
For both types, yeast is fully distributed through the beer while it is fermenting, and both equally flocculate (clump together and precipitate to the bottom of the vessel) when fermentation is finished. By no means do all top-cropping yeasts demonstrate this behaviour, but it features strongly in many English yeasts that may also exhibit chain forming (the failure of budded cells to break from the mother cell), which is in the technical sense different from true flocculation. The most common top-cropping brewer's yeast, Saccharomyces cerevisiae, is the same species as the common baking yeast. However, baking and brewing yeasts typically belong to different strains, cultivated to favour different characteristics: baking yeast strains are more aggressive, in order to carbonate dough in the shortest amount of time; brewing yeast strains act slower, but tend to tolerate higher alcohol concentrations (normally 12–15% abv is the maximum, though under special treatment some ethanol-tolerant strains can be coaxed up to around 20%). Modern quantitative genomics has revealed the complexity of Saccharomyces species to the extent that yeasts involved in beer and wine production commonly involve hybrids of so-called pure species. As such, the yeasts involved in what has been typically called top-cropping or top-fermenting ale may be both Saccharomyces cerevisiae and complex hybrids of Saccharomyces cerevisiae and Saccharomyces kudriavzevii.
Conditioning
After an initial or primary fermentation, beer is conditioned, matured or aged, [126] in one of several ways, [127] which can take from 2 to 4 weeks, several months, or several years, depending on the brewer's intention for the beer. The beer is usually transferred into a second container, so that it is no longer exposed to the dead yeast and other debris (also known as "trub") that have settled to the bottom of the primary fermenter. This prevents the formation of unwanted flavours and harmful compounds such as acetylaldehyde.
- Kräusening
Kräusening is a conditioning method in which fermenting wort is added to the finished beer. The active yeast will restart fermentation in the finished beer, and so introduce fresh carbon dioxide; the conditioning tank will be then sealed so that the carbon dioxide is dissolved into the beer producing a lively "condition" or level of carbonation. The kräusening method may also be used to condition bottled beer.
- Lagering
Lagers are stored at cellar temperature or below for 1–6 months while still on the yeast. [130] The process of storing, or conditioning, or maturing, or aging a beer at a low temperature for a long period is called "lagering", and while it is associated with lagers, the process may also be done with ales, with the same result – that of cleaning up various chemicals, acids and compounds. [131]
- Secondary fermentation
During secondary fermentation, most of the remaining yeast will settle to the bottom of the second fermenter, yielding a less hazy product.
- Bottle fermentation
Some beers undergo an additional fermentation in the bottle giving natural carbonation. [133] This may be a second or third fermentation. They are bottled with a viable yeast population in suspension. If there is no residual fermentable sugar left, sugar or wort or both may be added in a process known as priming. The resulting fermentation generates CO2 that is trapped in the bottle, remaining in solution and providing natural carbonation. Bottle-conditioned beers may be either filled unfiltered direct from the fermentation or conditioning tank, or filtered and then reseeded with yeast.
- Cask conditioning
Filtering
Filtering the beer stabilizes the flavour, and gives beer its polished shine and brilliance. Not all beer is filtered. When tax determination is required by local laws, it is typically done at this stage in a calibrated tank. There are several forms of filters, they may be in the form of sheets or "candles", or they may be a fine powder such as diatomaceous earth, also called kieselguhr. The powder is added to the beer and recirculated past screens to form a filtration bed.
Filters range from rough filters that remove much of the yeast and any solids (e.g., hops, grain particles) left in the beer, to filters tight enough to strain colour and body from the beer. Filtration ratings are divided into rough, fine, and sterile. Rough filtration leaves some cloudiness in the beer, but it is noticeably clearer than unfiltered beer. Fine filtration removes almost all cloudiness. Sterile filtration removes almost all microorganisms.
Packaging
Packaging is putting the beer into the containers in which it will leave the brewery. Typically, this means putting the beer into bottles, aluminium cans, kegs, or casks, but it may include putting the beer into bulk tanks for high-volume customers.
By-products
Spent grain, a brewing by-product
Brewing by-products are "spent grain" and the sediment (or " dregs") from the filtration process which may be dried and resold as "brewers dried yeast" for poultry feed, [139] or made into yeast extract which is used in brands such as Vegemite and Marmite. The process of turning the yeast sediment into edible yeast extract was discovered by German scientist Justus Liebig.
Brewer's spent grain (also called spent grain, brewer's grain or draff) is the main by-product of the brewing process;[142] it consists of the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process. As it mainly consists of carbohydrates and proteins, and is readily consumed by animals,spent grain is used in animal feed. Spent grains can also be used as fertilizer, whole grains in bread, as well as in the production of flour and biogas. Spent grain is also an ideal medium for growing mushrooms, such as shiitake, and already some breweries are either growing their own mushrooms or supplying spent grain to mushroom farms. Spent grains can be used in the production of red bricks, to improve the open porosity and reduce thermal conductivity of the ceramic mass.
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