Brewing

The brewing process

There are several steps in the brewing process, which include malting, milling, mashing, lautering, boiling, fermenting, conditioning, filtering, and packaging.

Malting is the process where the barley grain is made ready for brewing. Malting is broken down into three steps, which help to release the starches in the barley. First, during steeping, the grain is added to a vat with water and allowed to soak for approximately 40 hours. During germination, the grain is spread out on the floor of the germination room for around 5 days. The goal of germination is to allow the starches in the barley grain to breakdown into shorter lengths. When this step is complete, the grain is referred to as green malt. The final part of malting is kilning. Here, the green malt goes through a very high temperature drying in a kiln. The temperature change is gradual so as not to disturb or damage the enzymes in the grain. When kilning is complete, there is a finished malt as a product.

The next step in the brewing process is milling. This is when the grains that are going to be used in a batch of beer are cracked. Milling the grains makes it easier for them to absorb the water that they are mixed with and which extracts sugars from the malt. Milling can also influence the general characteristics of a beer.

Mashing is the next step in the process. This process converts the starches released during the malting stage, into sugars that can be fermented. The milled grain is dropped into 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. The leftover sugar rich water is then strained through the bottom of the mash in a process known as lautering. Prior to lautering, the mash temperature may be raised to about 75 °C (165-170 °F) (known as a mashout) to deactivate enzymes. Additional water may be sprinkled on the grains to extract additional sugars (a process known as sparging).

At this point the liquid is known as wort. 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 and technical reactions take place, and where important decisions about the flavour, colour, and aroma of the beer are made.

After the whirlpool, the wort then begins the process of cooling. This is when the wort is transferred rapidly from the whirlpool or brew kettle to a heat exchanger to be cooled. The heat exchanger consists of tubing inside a tub of cold water. It is very important to quickly cool the wort to a level where yeast can be added safely.

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.

The second to last stage in the brewing process is called racking. This is when the brewer racks the beer into a new tank, called a conditioning tank. There are two main methods - infusion mashing, in which the grains are heated in one vessel; and decoction mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature. Mashing involves pauses at certain temperatures (notably 45°C, 62°C and 73°C), and takes place in a "mash tun" - an insulated brewing vessel with a false bottom. The end product of mashing is called a "mash".

Mashing usually takes 1 to 2 hours, and during this time the various temperature rests activate different enzymes depending upon the type of malt being used, its modification level, and the intention of the brewer. The activity of these enzymes convert the starches of the grains to dextrins and then to fermentable sugars such as maltose. A mash rest from activates various proteases, which break down proteins that might otherwise cause the beer to be hazy. This rest is generally used only with undermodified (i.e. undermalted) malts which are decreasingly popular in Germany and the Czech Republic, or non-malted grains such as corn and rice, which are widely used in North American beers. A mash rest at activates β-glucanase, which breaks down gummy β-glucans in the mash, making the sugars flow out more freely later in the process. In the modern mashing process, commercial fungal based β-glucanase may be added as a supplement. Finally, a mash rest temperature of is used to convert the starches in the malt to sugar, which is then usable by the yeast later in the brewing process. Doing the latter rest at the lower end of the range favors β-amylase enzymes, producing more low-order sugars like maltotriose, maltose, and glucose which are more fermentable by the yeast. This in turn creates a beer lower in body and higher in alcohol. A rest closer to the higher end of the range favors α-amylase enzymes, creating more higher-order sugars and dextrins which are less fermentable by the yeast, so a fuller-bodied beer with less alcohol is the result. Duration and pH variances also affect the sugar composition of the resulting wort.

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Lautering

Boiling

The boil must be conducted so that it is even and intense. The boil lasts between 50 and 120 minutes, depending on its intensity, the hop addition schedule, and volume of water the brewer expects to evaporate.

Boiling equipment

Most breweries use a steam-fired kettle, which uses steam jackets in the kettle to boil the wort. The steam is delivered under pressure by an external boiler.

State-of-the-art breweries today use many interesting boiling methods, all of which achieve a more intense boiling and a more complete realisation of the goals of boiling.

Many breweries have a boiling unit outside of the kettle, sometimes called a calandria, through which wort is pumped. The unit is usually a tall, thin cylinder, with many tubes upwards through it. These tubes provide an enormous surface area on which vapor bubbles can nucleate, and thus provides for excellent volitization. The total volume of wort is circulated seven to twelve times an hour through this external boiler, ensuring that the wort is evenly boiled by the end of the boil. The wort is then boiled in the kettle at atmospheric pressure, and through careful control the inlets and outlets on the external boiler, an overpressure can be achieved in the external boiler, raising the boiling point by a few Celsius degrees. Upon return to the boil kettle, a vigorous vaporization occurs. The higher temperature due to increased vaporization can reduce boil times up to 30%. External boilers were originally designed to improve performance of kettles which did not provide adequate boiling effect, but have since been adopted by the industry as a sole means of boiling wort.

Modern brewhouses can also be equipped with internal calandria, which requires no pump. It works on basically the same principle as external units, but relies on convection to move wort through the boiler. This can prevent overboiling, as a deflector above the boiler reduces foaming, and also reduces evaporation. Internal calandria are generally difficult to clean.

Whirlpooling

In most large breweries, there is a separate tank for whirlpooling. These tanks have a large diameter to encourage settling, a flat bottom, a tangential inlet near the bottom of the whirlpool, and an outlet on the bottom near the outer edge of the whirlpool. A whirlpool should have no internal protrusions that might slow down the rotation of the liquid. The bottom of the whirlpool is often slightly sloped towards the outlet. Newer whirlpools often have "Denk rings" suspended in the middle of the whirlpool. These rings are aligned horizontally and have about 75% of the diameter of the whirlpool. The Denk rings prevent the formation of secondary eddies in the whirlpool, encouraging the formation of a cohesive trub cone in the middle of the whirlpool. Smaller breweries often use the brewkettle as a whirlpool.

Hopback

In the United Kingdom, it is common practice to use a hopback to clear the green wort (green wort is wort to which yeast has not yet been added). This device has the same effect as, but operates in a completely different manner than, a whirlpool. The two devices are often confused but are in function, quite different. While a whirlpool functions through the use of centrifugal forces, a hopback uses a layer of fresh hop flowers in a confined space to act as a filter bed to remove trub (pronounced tr-oo-b, tr-uh-b in the UK). Furthermore, while a whirlpool is only useful for the removal of pelleted hops (as flowers don't tend to separate as easily), hopbacks are generally used only for the removal of whole flower hops (as the particles left by pellets tend to make it through the hopback.)

Wort cooling

Another common method of energy recovery takes place during the wort cooling. When cold water is used to cool the wort in a heat exchanger, the water is significantly warmed. In an efficient brewery, cold water is passed through the heat exchanger at a rate set to maximize the water's temperature upon exiting. This now-hot water is then stored in a hot water tank. This distinction was introduced by the Dane Emil Christian Hansen. Top cropping yeasts are so called because they form a foam at the top of the wort during fermentation. They can produce higher alcohol concentrations and in higher temperatures, typically , produce fruitier, sweeter beers. An example of a top cropping yeast is Saccharomyces cerevisiae. Bottom cropping yeasts are typically used to produce lager-type beers. These yeasts ferment more sugars, creating a dryer beer, and grow well at low temperatures. An example of bottom cropping yeast is Saccharomyces pastorianus, formerly known as Saccharomyces carlsbergensis.

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 top-fermenting yeasts which may also exhibit chain forming (the failure of budded cells to break from the mother cell) which is technically 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 produce fewer off-flavours and tolerate higher alcohol concentrations (with some strains, up to 22%).

To ensure purity of strain, a "clean" sample of brewing yeast is sometimes stored, either dried or refrigerated in a laboratory. After a certain number of fermentation cycles, a full scale propagation is produced from this laboratory sample. Typically, it is grown up in about three or four stages using sterile brewing wort and oxygen.

Warm fermenting

Cool fermenting

Though it is the cool fermenting that defines lager, the main technical difference with lager yeast is its ability to process raffinose (a trisaccharide composed of the sugars galactose, fructose, and glucose) which means that all sugars are fermented, resulting in a well attentuated beer; top-fermenting yeast only cleaves and ferments the fructose portion of raffinose, leaving melibiose, which it cannot further cleave into two monosaccharides due to its lack of melibiase and the beer is sweeter with a lower conversion of sugar into alcohol. Raffinose is a minor dry component of Carlsberg barley, but once malted is practically nonexistent.

While the nature of yeast was not fully understood until Emil Hansen of the Carlsberg brewery in Denmark isolated a single yeast cell in the 1800s, brewers in Bavaria had for centuries been selecting cold-fermenting lager yeasts by storing ("lagern") their beers in cold alpine caves. The process of natural selection meant that the wild yeasts that were most cold tolerant would be the ones that would remain actively fermenting in the beer that was stored in the caves. Some of these Bavarian yeasts were brought back to the Carlsberg brewery around the time that Hansen did his famous work.

Today, lagers represent the vast majority of beers produced, the most famous being a light lager called Pilsner which originated in Pilsen, Czech Republic (Plzeň in Czech). Lagers range from very light to deep black.

Lager yeast normally ferments at a temperature of approximately 5 °C (40 °Fahrenheit). Lager yeast can be fermented at a higher temperature normally used for top-fermenting yeast, and this application is often used in a beer style known as "steam beer". Saccharomyces pastorianus is used in the brewing of lager

Spontaneous fermentation

Brettanomyces is a genus of yeast important in brewing lambic, a beer produced not by the deliberate addition of brewer's yeasts, but by spontaneous fermentation with wild yeasts and bacteria.

Secondary fermentation

Bottle fermentation Some beers undergo a fermentation in the bottle, giving natural carbonation. 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 may be added. The resulting fermentation generates CO₂ which is trapped in the bottle, remaining in solution and providing natural carbonation.

Cask conditioning Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer which is conditioned (including secondary fermentation) and served from a cask without additional nitrogen or carbon dioxide pressure.

Conditioning

Conditioning can take from 2 to 4 weeks, sometimes longer, depending on the type of beer. Additionally lagers, at this point, are aged at near freezing temperatures for 1–6 months depending on style. This cold aging serves to reduce sulfur compounds produced by the bottom-fermenting yeast and to produce a cleaner tasting final product with fewer esters.

If the fermentation tanks have cooling jackets on them, as opposed to the whole fermentation cellar being cooled, conditioning can take place in the same tank as fermentation. Otherwise separate tanks (in a separate cellar) must be employed. This is where aging occurs.

Filtering

Filters come in many types. Many use pre-made filtration media such as sheets or candles, while others use a fine powder made of, for example, diatomaceous earth, also called kieselguhr, which is introduced into 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. Normally used 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 gives a glass of beer that you could read a newspaper through, with no noticeable cloudiness. Finally, as its name implies, sterile filtration is fine enough that almost all microorganisms in the beer are removed during the filtration process.

;Sheet (pad) filters These filters use pre-made media and are relatively straightforward. The sheets are manufactured to allow only particles smaller than a given size through, and the brewer is free to choose how finely to filter the beer. The sheets are placed into the filtering frame, sterilized (with hot water, for example) and then used to filter the beer. The sheets can be flushed if the filter becomes blocked, and usually the sheets are disposable and are replaced between filtration sessions. Often the sheets contain powdered filtration media to aid in filtration.

It should be kept in mind that pre-made filters have two sides. One with loose holes, and the other with tight holes. Flow goes from the side with loose holes to the side with the tight holes, with the intent that large particles get stuck in the large holes while leaving enough room around the particles and filter medium for smaller particles to go through and get stuck in tighter holes.

Sheets are sold in nominal ratings, and typically 90% of particles larger than the nominal rating are caught by the sheet.

;Kieselguhr filters Filters that use a powder medium are considerably more complicated to operate, but can filter much more beer before needing to be regenerated. Common media include diatomaceous earth, or kieselguhr, and perlite.

Packaging

Brewing methods

References

Bibliography

External links

Category:Fermentation (food)