Decocting an Idea

At the beginning of this year, I made myself a couple of promises when is comes to my homebrew. Firstly I committing to brewing with Murphy & Rude malts as much as possible, partly because I want to support a local business, but also partly because I think fresher malt leads to better beer, and you can't get fresher than locally grown and malted grains. It also helps that Jeff and co now sell direct to homebrewers, so I can support Jeff's business directly, a fact that I very much like. My second promise to myself was that this would be the year when I finally start brewing lagers regularly, which meant buying a small chest freezer to be my fermentation and lagering chamber, and a desire to get to grips with the ins and outs of decoction mashing.

I know there are some who hold to the idea that decoction mashing is an un-necessary relic from the past, when malting technology wasn't at the level it is today, specifically when it comes to the levels of modification in the malt itself. The argument basically goes that since modern malts are more highly modified that in the distant past, then decoction mashing has become redundant as a way to maximise extract from the grains. I don't want to get into the weeds of Kolbach, Lintner, FAN, and all the other elements of malt - I am not being facetious there, malt is endlessly fascinating, from barley varieties to the levers a maltster has at hand to great unique products.

My biggest issue with the "decoction is not necessary" argument is that it makes a tacit assumption that the entire point of the mash is to extract as much fermentable sugar as possible from the grain and that it you really want some decoction character then just chuck in some Melanoidin malt - because most people won't tell the difference anyway. performing a decoction though is about more than just increasing the temperature in the mash from one rest to the next. If that were the sole aim of decoction, then just do a step mash. There is, however, magic in the boiling of the decoction...

The picture here is from my first stab at decoction mashing, the left hand side having just taken a third of the mash from the mash tun, and the right hand side, the same decoction after 30 minutes boiling. The boiling process creates a load of Maillard reactions, caramelising the sugars in the grain, adding depth of malt character. There is more to the mash than just getting your hands on sugars to pass on to the yeast for fermentation. The character might be elusive, it might be hard to nail down, and really define, but that doesn't mean negate its impact and value.

How then to do decoction mashing when your homebrew setup is basically brew in a bag? It helps to remember that the bag side of things, at least for me, is a cheaper and easier to use false bottom in a fairly traditional 5 gallon water cooler mash tun. I will admit that I was intimidated by the idea of trying decoction mashing, and my first couple of attempts were all over the place with learning about the properties of thermal mass and temperature loss in my mash tun, oh and it definitely helps to remember that the various rest temperatures are ranges rather than absolutes. 

My first time trying a decoction mash was a good lesson, I mashed in to give my grain a protein rest at 125°/51.6° and naively thought that my first decoction would spike the temperature to a saccharification rest of about 150°/65.5°. I was crestfallen when it "only" hit 144°/62.2°. Having drained the first runnings of my mash, I added my first load of sparge water, which only raised the temperature to 149°/65°, and even my second sparge only ever got the mash to 161°/71.6°.

As I have continued to learn, both through reading and by brewing, I have come to a couple of processes that seem to work for me, depending largely on the amount of time I have to commit to my brew day. If time is short, then I will do a single decoction, if plentiful then a double. My single decoction looks basically like this:

• Mash in for a saccharification rest at about 150°/65.5°
• Pull a third of thick mash after 30 minutes, and boil that for 30 minutes
• Returning boiling decoction hits mash out temperature of 160°/71.1°
• Let full mash sit for 30 minutes before draining and batch sparging, twice

A double decoction goes more like this:

• Mash in for beta-amylase saccharification rest at about 143°/61.6°
• Pull a third of thick mash after 30 minutes, and boil that for 30 minutes
• Return decoction to hit alpha amylase saccharification rest of 150°/65.5°, rest for 30 minutes
• Pull a third of thick mash, boil that for 30 minutes
• Return decoction to hit mash out at 160°/71.1°
• Let full mash rest for 30 minutes before draining and batch sparging, twice

So a 90 minute mash versus 150 minutes.

This may sound odd to some, but my lager brew days have by far been my favourites this year, and doing the decoction process makes for a more engaging day than the standard single infusion for my top fermented beers. It does help that when it is time to tap my lagers they look like these...