By Greig McGill

Surely, the mash is everyone’s favourite part of the brew day? I love the smell of hot grains, slowly unlocking their sweet potential as they steep in hot water. And that’s what the mash is for – allowing the various enzymes present in the malt to convert those pesky polysaccharides (starch) into the much more soluble, digestible, and importantly, fermentable sugars we need to feed our friends the yeast.

But what of the different types of mash? Does the mash type you choose matter? Should you use one type of mash for a specific beer style and a different one for the next? Oh boy, here be dragons…

For the purposes of this article, I’m going to try to stick to established practices and current knowledge. I’m not going to pick winners or wade into any holy wars! Things get heated (no pun intended) when talking about technique, as individual brewers often believe very strongly in what works for them. With that feeble disclaimer out of the way, let’s crack into it!

Single infusion mash

The “old faithful” of most brewers, including yours truly, single infusion is the simplest form of mash. You target your desired mash temperature, and you calculate the amount and temperature of your strike water based on the heat capacity of your mash tun, the temperature and quantity of your grain, and the ambient temperature, then you have at it! Infuse X litres of water at temperature Y with Z kg of grain and you’re done. Enzymatic activity is generally a “worst of all possible worlds” scenario, due to having to compromise between the optimal temperature ranges for each enzymatic reaction. At the end of it though, you will have a decently fermentable wort which will happily ferment into a great example of any style you choose. 

Step mash

A more advanced form of mash, designed to hit several increasing temperature steps (known as “rests”) for short periods of time over the duration of the mash. This is designed to promote or reduce different enzymatic activity or other chemical reactions during the different rests, and gives extremely fine control over the resulting wort. There are very few situations where you need a step mash, but you’re a home brewer. You get to play around with anything you like in search of the best beer you can make! Why not, eh?

Decoction mash

The decoction mash is a variant of the step mash, but a portion of the mash is removed, raised to boiling, and then re-added to the main mash in order to raise the temperature to hit each step. A two-step mash would be an infusion, followed by a decoction to raise to the second step. This is known as a single decoction mash. Double and triple decoctions are reasonably common also, with a triple being reserved for a four-step mash – now that’s control! It’s also a recipe for a very long and potentially messy brew day!

So why would you use each type of mash?

The single infusion mash is an excellent workhorse. It’s very easy to dial in a consistent result with it, and as most modern malts are so well modified and often highly diastatic (possessing plenty of enzymatic potential for starch to sugar conversion), fiddling around with step or decoction mashes can often be more trouble than it is worth. Most brewers should be able to brew every style of beer they wish using this simple mash method and still make gold medal worthy beer.

Step mashing can be sexy though! Historically, malts were often under-modified. That is, there was less breaking down of glucans and proteins during the malting process, leading to potentially much hazier and less stable beer, as well as not providing as many amino acids which contribute to yeast health. To work around this, brewers would “finish the maltsters’ work” by performing a step mash. The various stages of this were: acid rest (sometimes followed by a  specific ferulic acid rest), protein rest, and starch conversion rest.

The acid rest was designed to break down the glucans, preventing gumming up of the wort, as well as lowering the pH of the mash. A slightly higher temperature acid rest was designed to produce ferulic acid, a precursor to 4-vinyl-guiacol, the clove-like phenolic character, desirable in some wheat beers.

The protein rest was intended to degrade haze-forming proteins which not only look bad, but cause flavour instability. It will also degrade beta-glucans, which will help with very “gummy” mashes, but can also cause problems with head retention.

Finally, the starch conversion rest is where you get the good stuff! It’s where alpha and beta amylase (as well as limit dextrinase, a minor player at most mash temperatures, but increases the fermentability of your wort) are active, chopping up those long chain starches and converting them to the smaller and more fermentable sugars, maltose, and maltotriose. This is the only rest in a single infusion mash.

So, why would you use a step mash? Say you’re playing around with your own home-made malt, and haven’t achieved the modification levels the pros get – an ideal scenario for a step mash. Perhaps you want to play with heirloom grains, or other fermentables – design a custom step mash for the best beer you can make with those ingredients. Maybe you want to make the world’s best hefeweizen? A step mash with a ferulic acid rest will make an excellent example. You may even want to do that one using a decoction mash!

Speaking of decoction mashing, that’s where the real holy wars start! Proponents claim that you get much more “malty” character by using a decoction mash. This certainly makes sense, given the boiling of portions of the grain will involve the maillard reaction, producing a browning in colour and associated melanoiden production. Detractors will argue that you can’t taste any difference in a blind taste test, while others admit that you can, but that using a small proportion of melanoiden malt is a much easier way to achieve the same effect. Some just enjoy the historical nature of the process, and the smells associated with it. There is no “best practice” here – do what makes you happy as a brewer.

So there you are! After all that, you have hopefully decided on your mash regime of choice for your next SOBA NHC winning beer. I guess you need to start thinking about sparging that bad boy… but that’s a whole other discussion!