Brewing with Constraints: Decoction Mashing

Noble Hop, a local homebrew shop, decided to run a “for fun” brewing competition called “Iron Brewer”. The entry fee was only 20 bucks so V and I decided we’d give it a shot. We were given 10 lbs of 2-row along with 3oz of Cascade hops. We are allowed to choose whatever yeasts or bacterias we wanted, but couldn’t add anything else (no fruit additions, oak chips, etc).

Simply using 2-row would result in a pretty pale beer, and we were hoping to do more of a Pale Ale / IPA with the ingredients. Some other brewers were going to bake some of their grains to simulate more roasted malts, but we decided we’d give decoction mashing a try again. We knew that it was going to increase the length of our brew day, so we decided we’d spend our Canada Day brewing beer.

Decoction mashing is an old brewing technique that was used back when grain wasn’t as advanced as they are today. It involves doing a series of mashing steps where parts of the mash would be removed from the mash tun and cooked (decocted) for a certain amount of time. This technique for mashing was required because the old malts weren’t as well modified as they are today. In order to improve extraction brewers found that by pulling out some of the mash they could get a better beer. This was because the act of boiling part of the mash helped break down cell walls and made the starches within them more accessible. An added of this technique was it aided in consistent mashing temperatures before we had thermometers. Cooking also extracts melanoidins from the grain husks, adding colour to the mash and finally our beer.

We performed a double decoction, so we’d be pulling our mash twice and boiling it for a period of time before adding it back. We had three targets to hit for our mash:  35℃, 50℃ and 65℃. While hitting these various phases isn’t super important with the kinds of grains we have nowadays, these temperatures helper trigger a bunch of enzymatic action which breaks down the starches into sugars. Back in the day they didn’t really know why these were important, but it helped make the beer better and yield sweeter wort. Today though we know what is happening and have named them appropriately: Beta Glucanase phase (35-40℃), Proteolytic Enzyme phase (aka Protein Rest, 45 – 55℃), Mash Phase (~65℃) which activates the Alpha and Beta amylase enzymes to help with that maltose production.

For us though, we were mostly interested in getting that colour and experiencing what this mashing process is like. It’s time consuming and pretty boring for the most part, you spend a lot of time mixing your grains while they cook to prevent scorching. Along with that, the constant stirring is exhuasting and dangerous because of all the hot steam coming off the decoction.

When decocting it is important to be sure as little liquid is removed from the mash as possible. That liquid contains all the enzymes responsible for breaking down our starches, and bringing them to a boil will destroy them and result in a lower yield. While pulling out our decoction we tried out best to gently push as much liquid out of our mash as possible. If our decoction got too dry, we added a bit of boiling water from our kettle to loosen it up and prevent the scorching. Decoctions aren’t short either: our first decoction involved a 45 minute boil while our second was a 30 minute boil. V and I traded stirring responsibilities every 10 minutes to give our arms a rest.

Our software was giving us guidelines as to how much mash to pull as well as what our targets should’ve been when we poured the decoction back into the mash tun, but we had a hard time hitting them. Something we took note of for next time was to ensure we have a decent amount of boiling water available so we can re-adjust if we are off our targets.

The rest of the brewing day went off without a hitch and we got about 80% efficiency from our mash. Some other articles I read stated that you should see about a 5% increase in efficiency, and typically we’ve gotten around 75% so the decoction did help.

Would we consider doing it again? Only for special occasions. It’s a time consuming way to do things and while it is the recommended mash method for most European styles, there are limitless combinations of malts you can use to brew and that won’t take as much time. It is, however, an interesting way to mix it up and trying a new technique.

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About Chris

If there is a place that serves or sells beer I've never heard of, I'll find a way to get there. A fan of the humble Pale Ale, though always willing to try a pint of something new. I also enjoy brewing my own beers and love sharing the science of the beer making process.