Brewing Processes - Mashing
Mashing is the first major step in the brewing process. It is the process of mixing milled (crushed) malt with hot water and letting it rest for a period of time. The goal of mashing is to extract the complex sugars from the malt and break them down into simpler sugars. The resulting sugary liquid is called ‘wort’. We can modify the conditions of mashing in a number of ways to impact the final beer. A basic understanding of mash chemistry is a good start for mastering this process.
A quick word on malt sugars
Glucose is a single chain sugar (monosaccharide) which can be found alone or forming chains of varying lengths. Extremely long glucose chains (starches) make up the majority of sugars found in malt. Other sugars found in malt and wort include glucose, maltose (two glucose units), maltotriose (three glucose units), dextrins (longer glucose chains). Fructose is another single chain sugar found in small amounts in malt, as well as sucrose which is a fructose molecule bonded to a glucose molecule.
Breaking down sugars
The complex long-chain starches in malt are broken down to simpler shorter-chain sugars by a number of enzymes from the malt in the presence of water. The process isn't as simple as mixing the two ingredients as the enzymes are only active at certain temperatures. The most important enzymes for sugar breakdown (saccharification) are β-amylase and α-amylase which work optimally at 60-63°c and 68-72°c respectively.
If we consider a starch molecule, which is a long chain of glucose molecules bonded together and tighly bound in a crystalline structure, the structure must first be ‘gelatinised’ to allow the enzymes to work. Gelatinisation is the unwinding of the starch structure in the presence of water and heat to give the enzymes access to the chain. This is easy in a barley mash as the starch gelatinises above 58-62°c, which is a given at any typical mash temperature. Other cereals such a rice and corn have a much higher gelatinisation temperature and must be cooked or processed prior to mashing. Once the starch is gelatinised, the amylase enzymes can then begin to break them down into many shorter glucose chains.
The two amylase enzymes work in different ways. β-amylase attacks the second bond from the end of the chain and cleaves off two glucose units. α-amylase on the other hand attacks the chain at random points and breaks it down to chains of varying lengths.
Given the correct conditions and enough time the enzymes will break down all the starch forming a range or shorter chain sugars which dissolve in the liquid. A typical all-malt wort sugar composition can be seen in the graph below.
The purpose of extracting the sugars from malt is to provide yeast with a carbon source to produce alcohol and a number of other byproducts in fermentation. The starches and dextrins cannot be utilised by most yeast, leaving only the simpler sugars available for yeast to use. Luckily in mashing the starches were broken down largely into sugars which the yeast can ferment. The wort shown above is approximately 88% fermentable and 12% unfermentable to most yeast strains. The residual sugar which isn’t fermented contributes to the body and mouthfeel of a beer. Beers with less body generally feel thinner and less full in your mouth, while the opposite is generally true for beers with more unfermentable sugars.
Manipulating fermentability in the mash
The mash time and temperature are the key variables used to manipulate wort fermentability. In simple mash programmes which only include one temperature rest a single mash temperature is chosen to affect the wort fermentability. A lower temperature (around 65°c) allows both α-amylase and β-amylase to work on breaking down starches to simple sugars and produce a highly fermentable wort given enough time. In the same time period a higher mash temperature (around 69°c) will favour α-amylase action but limit β-amylase. The resulting wort will be less fermentable due to more leftover unfermentable sugars.
A typical home brewer’s mash is sixty minutes, allowing plenty of time for the enzymes to break down complex sugars. A less common approach to adjusting wort fermentability is to adjust the mash time as opposed to temperature. For example, mashing at 65°c for fifteen minutes will likely produce a beer with more body than the same mash for sixty minutes. Conversely, mashing at 72°c will denature β-amylase, but given enough time α-amylase alone could still theoretically produce a highly fermentable wort.
In a more complex mash regime employed by commercial breweries, multiple temperature rests for specific time periods are used to maximise the action of certain enzymes and achieve a very predictable composition of wort sugars in a shorter amount of time.
Wort sugars and yeast
The relationship between yeast strain and wort sugar composition is worth mentioning here. While as a general rule most yeast will ferment all of the sugars mentioned above with the exception of the long-chain unfermentable sugars, some notable exceptions exist. Some yeast strains cannot utilise maltotriose, meaning a higher degree of the wort is unfermentable and more body will remain in the beer. On the other hand some yeast called ‘Diastaticus’ can produce the enzyme amyloglucosidase which can degrade starches to glucose. The resulting wort may therefore become totally fermentable despite the initial presence of unfermentable sugars.
To sum it up, mashing is an extremely important part of the brewing process. It is the step which we take unfermentable sugars and turn them into the fermentable sugars that yeast can use to make beer. While there are complex processes occurring at a chemical level, simply controlling the basic parameters like temperature will go a long way in producing the right wort for each brew.