Reiterated Mashing: Practical Advice


A diagram of how reiterated mashing can work at home.

Yesterday I introduced my idea of reiterated mashing, inspired by the brewers of Samichlaus. (I say, “my idea,” but I’m sure many brewers through history have had similar thoughts. In his book, “Radical Brewing,” Randy Mosher describes the same basic idea from early England.)

The basic idea is to use wort as your brewing liquor for a high-gravity batch of beer. So, you mash once to make your brewing “water” and again with wort to make your high-gravity wort.  One way to look at reiterated mashing, and to understand when you might want to use it, is to compare how it concentrates the wort compared to other, standard ways of brewing.

To brew a big beer normally, you would collect a lot of wort and boil it for a long time. You would end up with a high-gravity wort because you boiled off lots of water. Another way to make a big beer is to add malt extract. In this case, the manufacturer of the malt extract would have boiled off (and otherwise evaporated) lots of water for you. In reiterated mashing, you don’t concentrate the wort in the kettle by applying heat and evaporating water; you concentrate the wort via simple diffusion in the mash tun. Because of this, you get much less color in the wort. You could brew a dark colored beer this way, but the other, “regular” ways of making a big beer would be faster. Reiterated mashing is best used for making a very high-gravity beer with very little color.

Practical Advice

I’ve made two 5.0-gallon (19-L) batches of beer this way and a third 3.0-gallon (11-L) batch. Plus, I’ve brewed two batches — one 5.0-gallon (19-L) and one 10-gallon (38-L) — that employed three mashes. Here’s the practical knowledge I’ve gained from that experience.


First Mash

With reiterated mashing, you’re in for a long brewday. So don’t prolong it by dragging out the first mash. After you mash in, start performing starch/iodine tests every 5 minutes or so and run off the wort as soon as one is negative (or even mostly negative). Mashing out to 168–170 °F (76–77 °C) is good, but don’t bother recirculating at this point. Run off the wort quickly. If you use continuous sparging, you’ll lose a bit of efficiency by running off quickly, but not much. Batch sparging is a great option or — if your mash tun holds a tun of liquid — no sparge mashing.

If possible, stir the mash often to help your extract efficiency. The better your extract efficiency, the higher in specific gravity your wort will be. As you would with any mash, adjust your water chemistry to hit the proper pH.

I run the first wort off into my hot liquor tank (HLT), then all the vessels are used for their normal purpose from that point on. If you aren’t set up to do this, run off to the kettle then pump your wort over to the HLT before mashing in the second mash. To prepare for the second mash, you don’t need to clean your mash tun until it’s spotless, just dump or scoop out the grain, rinse it, and proceed.


Second Mash

The most important thing I learned about the second mash is to give it time. The starches from the grain will dissolve, they will get converted to sugar and the specific gravity of your wort will rise — but it takes time. Stir the mash frequently and take specific gravity readings every 10 minutes or so. (Use a refractometer, if you have one.) You will see the specific gravity rise each sample, and then start to tail off.

It’s up to you when to stop mashing. Most of the time, I let the second mash go about 2 hours. If you write down the time and gravity of each sample, you’ll be able to estimate how many more “gravity points” 10 more minutes of mashing will give you. The usual stuff that applies to getting better extract efficiency applies here, but that goes double for stirring — this really helps in the second mash. (If you can’t heat your mash tun, you are at a bit of a disadvantage here. Adding hot water to keep your mash temperature up is counterproductive as you are trying to concentrate the wort in the mash tun.)

I’ve never done this, but if I had a mash tun that was well-insulated, an overnight mash might be a good thing in terms of extract efficiency.

When you combine the malted grains with your wort, add a small amount of calcium to the second mash. Figure out how much calcium was in your strike water for the first mash and add roughly that amount. The pH of your second mash is almost guaranteed to fall into the optimal range that way.

Given the high-gravity of the wort, you’ll want to mash for a highly-fermentable wort. I like to mash in the second mash at 140–145 °F (60–63 °C) and give it at least a 30 minute rest until heating the mash tun and ramping the temperature up to 152 °F (67 °C). This works well because the temperature of the brewing liquor is usually around 152 °F (67 °C) coming out of the mash tun. If you can’t heat your mash tun, heat the first wort and do a single infusion mash starting at 148 °F (64 °C).

Once you’ve decided the second mash is done, the rest of your brewday is fairly standard. Reirculate then begin running off the strong wort. Sparge with the wort from the first mash. This time around, using a slow, continuous sparge will help your extract efficiency. Using some water to rinse the grain bed right at the end would increase your extract efficiency, but at the expense of diluting your wort.

You can boil the wort however long you want, to reach whatever specific gravity you desire, but I usually only boil 60–90 minutes in order to keep the wort light in color. Adding about 50 ppm calcium to the boil will help with the hot break and minimize color pickup.

Tomorrow, I’ll post a recipe with step by step instructions on how to do this.




  1. Chris,
    The reiterated mash looks like it might be a good way to get a higher gravity beer done via BIAB when doing it in one step would require a larger vessel. Do you know if anyone has tried that?

  2. Thanks for this series of posts, Chris. I’ve had an idea to try something similar to this out to brew a super-high gravity barleywine using my hybrid-BIAB system. I brew 3-gallon BIAB batches using a separate 5-gallon cooler as a mash tun (instead of mashing in my kettle) to help hold temperature during the mash.

    My thought was to mash very high (160-162F) for the initial mash to favor alpha amylase. I would then pull my bag, dump it, then add it back with a second dose of grain. Hopefully this would put me in temperature range for a low beta-amylase rest (145ish), but I could always boost the temp a bit with some boiling water if needed. My theory is that you should be able to generate a more fermentable wort by letting alpha amylase go to work on the initial mash followed by a beta rest (which is something you wouldn’t normally be able to do as beta amylase starts to denature at alpha-rest temps).

    I have yet to try this out, but I’m planning to this fall/winter. Your posts have definitely given me some good food for thought. Thanks!

    • Chris Colby says

      Cool idea. Definitely try it. A “step down” mash might allow you to make a very fermentable wort, which in this case would be good. Also, the high temperature of the first mash would make for a quick conversion.

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