Mashing is an extraction process by which milled barley or malt (usually called grist) is combined with hot water and adjuncts (other cereal ingredients) to produce a fermentable substrate on heating, which provides all the necessary nutrients and precursors for yeast in the fermentation stage (Tse et.al 2003).
The main objective of the mashing process is to maximise the production of fermentable matter by:
· The enzymatic hydrolysis of the insoluble polysaccharide starch into fermentable carbohydrates (sugars).
· Breakdown of non-starch polysaccharides into smaller carbohydrate units eg beta-glucans and arabinoxylans (Durand et.al 2009).
· Degradation of storage proteins into amino acids and peptides, by the action of proteinases (Jones & Marinac 2002), which can contribute to a haze or foam in the beer (Scannell 2012).
· Increasing nitrogen compounds available for yeast to use during fermentation (Preedy 2009).
The different mashing processes available to a developing brewer are:
The infusion mashing system is normally used by traditional British ale brewers. This system is very simple compared to other methods, in terms of number of vessels used and takes place in a single vessel only, called mash tuns (Hough1991), where the conversion and separation of the sweet wort from spent grains take occurs. The texture of infusion mash differs from others as a thick, viscous mash is produced at around 63-67°C by mashing coarsely ground grist (Briggs et.al 2004), containing a large quantity of well-modified malt with a maximum of 10% adjuncts (Hough1991). The liquid wort is removed from the mash, after a standing for 30 mins to 2 and half hours. This wort is re-circulated as it is cloudy and then then runoff becomes clear due to the filtering action through the grist particles. This clear wort is then collected in a holding vessel or transported to a copper where it is boiled with hops. The residual extract, which is carried along in the wet grains, is washed out by spraying hot liquor, at 75-80ºC over the goods (Briggs et.al 2004) Protein rests are not normally used because temperature steps are not employed and some types of beers such as wheat beer usually need a protein rest at lower temperatures, so they are more difficult to brew with this system (Colicchio et.al 2012). The maximum number of brews set in one vessel each day is normally five (Hough1991).
(b) Temperature-programmed infusion mashing system
Temperature-programmed infusion mashing is normally used by brewers in the UK and mainland Europe and has now started to replace older mashing systems. Finely ground grist and a thin mash are created to permit stirring. Mashing of the grist, containing poorly modified malt or sometimes well modified malt (Briggs et.al 2004) with 30-50% adjuncts (Hough1991), takes place in 1-3 stirred heated mash-mixing vessels, unlike single temperature infusion mash, which are externally heated to 35°C. Stands heat the mash at 50°C, 65°C and 75°C to give proteolysis and starch breakdown (Hough1991). Then a lauter tun or mash filter collects the sweet wort (Briggs et.al 2004). This system uses protein rest, unlike the infusion and double mash systems. The maximum number of brews set in one vessel each day is normally is 12-14, significantly larger than infusion mashing (Hough1991).
(c) Double mash system
The double-mashing system commonly used by North American brewers, which uses very well defined malts that are enzyme-rich and contain nitrogen and also large amounts of maize or rice grits (Briggs et.al 2004). This takes place in three vessels only. High levels of adjuncts are normally used for this process (30-50%) to make use of enzymes and dilute excess nitrogen compounds. This process involves mixing grits with a small amount of malt in a cereal cooker and heated to 65°C, where the viscosity of the mixture decreases due to the action of the malt enzymes, then is boiled unlike the other processes. Throughout this system, the starting temperature of the main malt mash is 45°C to promote starch breakdown and proteolysis. The content of the cereal cooker are transferred to the main mash and the temperature is increase to 67°C causing an increased breakdown of the malt and adjunct starch. To reduce viscosity the mash is heated to 72°C before been pumped into the lauter or mash filler in order to separate the wort. Like infusion mash systems, this system does not use a protein rest. The maximum number of brews set in one vessel each day is normally is 12-14, identical to temperature-programmed infusion mashing (Hough1991).
(d) Decoction system
Decoction mashing is a traditional system used by larger brewers in mainland Europe. Finely ground grist’s are used made from less modified malts. These mashes are very thin like temperature programmed systems, however they need to be moved by pumping and stirred. This system use 3-4 vessels, which include a stirred mash mixing vessel, a stirred decoction vessel and a device for separating the wort. An initial temperature of 35°C is achieved by mashing the grist. Decoction occurs after standing, where a third of the mash is pumped to a cooker and is heated to boiling point (Briggs et.al 2004). This is the only system that in which the boiling of the malt occurs, and is very important particularly for a less modified malt in order to breakdown the cell walls making the starches more readily accessible for the malt enzymes (Colicchio et.al 2012). The temperature rises to 50°C, when the boiling mash is pumped back into the mash mixing vessel and mixed with its contents. Decoction is carried out after a final stand, where the temperature is increased to 65°C then to 76°C for the final decoction. The mash is then moved to a lauter tun or a mash filter (device for separating the wort) where the sweet wort and spargings are collected, and boiled with hops. Like temperature-programmed infusion mashing, this system uses a protein rest. The maximum number of brews set in one vessel each day is normally is 8, making it the second largest amount of brews set after temperature-programmed infusion and double-mashing systems (Hough1991).
References
Briggs D.E, Boulton, C.A, Brookes, P.A and Stevens R (2004). Brewing Science and practice. Woodhead Publishing Limited, Cambridge, England.
Colicchio,T., Bamforth, C., Philliskirk, G., Villa, K., Stempfl, W & Hayes, P (2012). The Oxford Companion to Beer. Oxford University Press Inc, New York.
Durand, G.A., Corazza, M.L., Blanco, A.M., Corazza F.C. (2009). Dynamic optimization of the mashing process. Food Control, 20: 1127–1140.
Hornsey, I.S (1999). Brewing. Royal Society of Chemistry (Great Britain), RSC Paperback, Cambridge, UK.
Hough, J.S (1991).The biotechnology of malting and brewing, Cambridge University Press, New York.
Jones, L.B & Marinac, L (2002). The Effect of Mashing on Malt Endoproteolytic Activities. J. Agric. Food Chem. 5: 858-864.
Preedy,V.R (2009).Beer in health and disease prevention. Elsevier Inc, USA.
Scannell, Amalia (2012) Lecture material, file 5 – Yeast.
Tse, K. L., Boswell, C. D., Nienow, A. W. & Fryer, P. J (2003). Assessment of the Effects of Agitation on Mashing for Beer Production in a Small Scale Vessel. Trans IChemE, 81, Part C, 1-12.
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