Decoction Mashing, Part 2

Decoction Mashing, Part 2

Decoction Mashing at Home

(This post was restored from the old site, and contains some really good and knowledgeable information, and deserves to be kept up. If you are reading this David and would like it removed just contact us) Props to David for the awesome write-up.
By David Cordrey

In Part 1 of this subject I described what decoction mashing is, extolled it’s benefits, and gave a brief history of its origin and what styles showcase decoction mashing’s added character. In Part 2 I’ll describe the practical aspects of decoction mashing. This is a “How To” primer on the subject.

You may ask yourself “Why on earth would I want to do a decoction mash at home?” – I make damn good beer using infusion mashes. I use highly modified quality 2-row malt, I don’t need to decoct. I don’t want to hassle with a bunch of extra process steps to make my beer. I’m afraid I’d screw up a batch by boiling grains.

These are all valid points. But what if you wanted to make a killer Dopplebock? Adding Crystal and Munich malt to an infusion mash will help add sweetness, but just won’t give the same perceived maltiness as a decoction mash. What if you wanted to replicate the procedure to make a Bohemian Pilsner? Authenticity would dictate a decoction mash. What if you were making a Pale Ale or Bitter or any other style using an infusion mash and you missed your mash temperature? A small decoction could get you back on track without thinning out the mash excessively by just adding more hot water.

Decoction mashing is a technique that homebrewers should have in they’re repertoire. And believe me, it is easy to master. Once you get used to the technique, you’ll probably use it a lot!

What You’ll Need:

To get started you’ll need the following extra equipment:

  • A second stainless or enamel finished boiling pot at least one third the volume of your mash tun.
  • A large long handled slotted spoon or strainer.
  • A small approx. 1 to 2 quart size container (Tupperware works fine).
  • A heat source for boiling the decoction.

Chances are you have everything you need at home already. I use the small 3 gallon pot I started brewing in, a big plastic slotted spoon from the kitchen, a thoroughly cleaned quart size yogurt container and my Cajun Cooker.

How to Decoct

The big question in decoction mashing is how much mash do you pull out for boiling? If you don’t take enough mash the temperature rise will not be as great as desired; too much will result in overshooting your desired temperature. Fortunately there is a good “rule of thumb” to follow for decoction mashing:

Dough in using 1.33 qts. of water per pound of grain and stabilize at 122°F.
Use a thick portion of the mash consisting of 40% the quantity of grain in the decoction.
Temperature gain will be approximately 28°F per decoction.
This rule of thumb is easy to remember, and fits the temperature profile for a single decoction nicely. If you want a different temperature gain, you can calculate the decoction fraction as follows:

F = ( Tf – To ) / ( 212 – Tf- K )

Where: F is the fraction of the main mash to boil. (multiply by 100 to get %), To is the starting temperature in °F, Tf is the desired final temperature in °F, K is your temperature loss constant (17°F for my system). The value for K can be adjusted ± a few degrees to fit your own results.

When plotted in graphic format, the results look like this:

As can be seen, this formula predicts that as the starting temperature increases, a larger decoction needs to be pulled to result in the same temperature gain.

I always try use 1.33 quarts of water per pound of grain for both single infusion and decoction mashes – just as a matter of convention, not because this is a magic ratio. Different ratios can be used, but will affect the temperature gain because water and grain have different specific heats. For water/grain ratios of 1.25 to 1.5 qts/lb the above rule is close, however, and can be accommodated by changing the “K” term.

Detailed Procedure

Definition of a “thick mash” is a little tricky. It is important to allow the gain to become fully hydrated (absorb all of the water it can) before pulling the decoction. Stir the mash well and let it soak for 5 to 10 minutes at the initial rest temperature. Then using your large slotted spoon, scoop out the wet grain into your quart size cup and transfer to the small (cold) boiling vessel. The grain should pile up in a ball in the pot. Scoop out a third of the grain. I’ve found my 1 qt. container holds very close to a pound of dry grain. If I’m mashing 15 lbs. total, one third of that would be 5 scoops for the decoction. Now pull out some liquid from the main mash in your container and slowly add it to the pot until the pile of grain begins to slump. Stir it up, it should resemble the consistency of thick oatmeal, with some liquid between clumps of grain. Don’t forget to cover up and insulate the main mash. You don’t want it to cool off while you’re boiling the decoction!

Start the fire under the decoction mash and heat it up slowly, stirring constantly to prevent scorching. As it nears boiling, it will appear to thin out some and a scum layer will form on top. Keep it on a low boil for as long as you want to conduct the initial main mash rest, scraping the scum off occasionally, and stirring frequently. I generally boil for 20 to 30 minutes. Be careful not to scorch or burn the grain, add a little more liquid from the main mash if this looks like it might happen. The longer the boil, the more the flavor impact it will have; I’ve gone as long as 45 minutes with the decoction boil. A short boil will net the same temperature rise, but with less flavor impact.

Now carefully dump or scoop the decoction mash back into your mash tun. Try not to splash too much or spill it down the front of your shirt. If you wear glasses and can see Okay without them, take them off first. I’ve had a few near accidents when my glasses steamed up so bad I couldn’t see at all. Once you have successfully transferred the decoction back to the mash tun, stir it all up thoroughly and cover to let the temperature stabilize. You should wait at least 5 minutes before checking the temperature. Everything should be Okay now, just continue this rest for the desired time. That’s it for a single decoction mash. Just sparge and collect the wort like normal.

Multiple Decoctions–The Ultimate Experience

For multiple decoctions, just repeat the procedure to step through your temperature ranges. The 28°F rise described in the previous section fits nicely with the temperature step profile that is desired for a single decoction mash. If you dough in to achieve a 122°F first rest (protein rest), a single decoction will get you to the conversion rest temperature of ~150°F. A second decoction would heat the mash to above 170°F for a mash out. A triple decoction profile could be employed to rest at four different temperatures. The more decoctions you use will increase the number of melanoidin reactions and carmelization, and thus add more of the “malt character” that is associated with decoction mashing.

The possibilities are virtually unlimited as far as temperature profiles you can create. Traditionally the rest temperatures that are used with decoction mashing are as follows:

  • 95-110 °F Acid / Gluconase Rest
  • 120-127 °F Protein Rest
  • 145-159 °F Sacharification (conversion rest)
  • 170-178 °F Mash out

Which rest temperatures you want to hit, will determine the number of decoctions you will use. The most common decoction mashing profiles are:

Single Decoction: Mash in at the protein rest temperature. Use a single decoction to reach conversion temperature.

Double Decoction Mash: Mash in at the protein rest temperature. Use one decoction to reach conversion temperature, then a second decoction to mash out. Typically used for sweeter beers with a higher conversion temperature. The “mash out” destroys any residual enzymes that might further break down any dextrins during sparging.

Triple Decoction Mash: Mash in for an acid or glucanase rest, then perform three separate decoctions to hit each of the temperature ranges. An acid rest helps lower pH and thus starch conversion when using all pale malts and very soft water, such as might be the case when replicating a Bohemian Pilsner.

These rest temperatures were developed over a long time by trial and error to fit the circumstances faced by brewers hundreds of years ago. The merits of each rest and impact of what temperature to hit in each range are often debated and hence are subjects for another article. There are plenty of books covering this subject in detail. Papazian’s The New Complete Joy of Homebrewing is a good primer on this subject.

Go For It!

You now have all of the information you need to try decoction mashing on your very own. Go for it! Take the plunge. Really, your chance for failure is very, very small. Your chance for outstanding success is great. The temperature ranges are broad enough you’re going to end up somewhere in the ballpark. My experience is that I have never overshot by more than 2°F. When I err on the low side by 5°F or more I just do an extra, small quick decoction to get back on track.

Remember, proportionally smaller or larger decoction volumes will net lower or higher temperature rises. Short boil times will give the same temperature rise without affecting flavor or color very much. These facts are useful for making small temperature adjustments. So if you miss your target temperature in an infusion mash, use the formula or graph above and just pull a small decoction to boost it up a bit.

For certain styles, decoction mashing is the only way to get the “malt character” that is required. Decoction mashing also can give a pleasing complexity in styles that don’t traditionally use decoction mashes. Scotch Ales, for instance, can be easily given a malty finish through the use of a decoction mash.

Decoction mashing is a technique that is well worth mastering. You may not use it for every batch, but it should be in your repertoire for making traditional lagers & bocks, correcting mash temperatures, or adding malt character to any beer.

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