Mashing out. Lots of homebrewers don't do it; all homebrewer's should. Why? Many reasons. First of all, raise your hand if you have ever had a stuck sparge? One of the key benefits to mashing out is lowering the viscosity of the liquid inside your mash tun. In other works, thinning it. This is especially important if you are using lots of non-barley grains such as wheat or rye (or pretzels). Also, many brewers tend to mash at a 1 quart per pound of grain ratio. Which, if not hot enough, could stick. Better put, is more likely to stick. And by making the mash more fluid what you are really doing is making the sugars in the wort more fluid. So, you will extract more of them; mashouts give you better efficiency. Also, mashing out stops all enzymatic activity. So, if you just spent an hour mashing a highly fermentable beer at 149, you are not going to accidentally start producing non-fermentable "body" sugars when you start sparging. To conclude: there is no downside to a mashout.
The question then becomes "how do I perform a mashout?" That is the point of this article. There are of course several ways to mashout. If you have a direct-fired tun simply turn on the gas and start stirring. Those of you who use a cooler can opt to infuse the mash with a certain amount of hot or boiling water to achieve the desired mashout temperature of 168. You can also use a HERMS or a RIMS setup where the mash temperature is slowly raised. All of these work. However, there is a fourth option; using a decoction to reach mashout.
A decoction is where you remove part of the Mash and boil it in a kettle. This is most commonly used when making Hefes or continental lagers such as Pilsners, Viennas/Marzens and Bocks. Those beers really benefit from decoctions because they use less modified malts or in the case of Hefes, wheat, which has its own problems (see Eric Werner's German Wheat Beers for more on the challenges of working with wheat). But what if you are making an IPA? Or a Barleywine? Would a decoction do anything for you? Yes. Technically speaking (and outright stealing from fellow Falcon Darryl Richman's book Bock), "A decoction mash continues the melanoidin building process, aids in protein breakdown and coagulation, and maximizes the gelatinization of the starches in the malt." In other words, decoctions make your beer maltier, clearer and higher in sugars. Ain't nothing wrong with any of that.
Now, the rub with decoctions is that they are not fun. Unless you are Steve Cook (who claims that he can decoct one handed while surfing the internet) you will find decoctions to be a pain in the rump. The constant stirring over a hot flame is no one's idea of fun. So why bother? That is to say, why bother with a thick decoction that has to be nannied constantly; why not instead just pull a thin decoction that can be left alone while boiling? I'm talking real thin (keeping in mind that you will not get the full benefit of a thick decoction with this method). Here's how it works: After the starch has converted, drain off a portion of the wort (we'll get to exactly how much in a minute). Drain it through a mesh-strainer -- the kind you would use to skim off scum. There's no need to perform a Vorlauf at this point because all the wort you collect (minus some steam that gets boiled off) is going right back into the tun eventually. By removing whatever husks and grains drain out, you can just simply boil the wort. How long do you boil it for? As long as you feel necessary. This is where the art comes in. I typically let decoctions for mashouts go for fifteen minutes. The longer you boil for, the more caramelized your wort becomes. Then, you simply re-infuse your freshly decocted portion of the wort back into the tun, give it a stir and voila, mashout.
This is the process I use, and have gotten good results from. Let's assume we're making a 10-gallon batch using 30 pounds of grain. A 1-quart to 1-pound ratio would call for 7.5 gallons of strike water. Since we are going to be performing a decoction, I would instead recommend 1.5-quarts per pound, meaning that we will need 11.25 gallons of strike water. Let that mash for half an hour (or until conversion is complete), then drain out 4 gallons of wort for the decoction. 3.75 gallons if you want to be technical. Why 3.75 gallons? Because when you remove that amount, the volume of liquid remaining in the tun is 7.5 gallons; the volume that would be needed for a 1:1 quart/pound ration. By leaving in that volume of liquid, you are not in danger of drying out (and cooling off) or compacting your grain bed.
To recap, the metric is to use 1.5-quarts of water per pound of grain, pull 1/3 of that volume through a strainer and into a kettle, boil, and then re-infuse the decocted wort back into the tun. Simple as pie. One issue might be that if you are mashing a beer low -- say at 149 or thereabouts -- 33% of the liquid may only raise the mash temperature to 165 degrees. So, account for this initially by mashing at say 1.65-quarts per pound and pull out a little more juice. Conversely, if you are mashing high at say 158 degrees, 33% might be too much. In that case, all you need pull is 25-30% or so. As far as added time goes, this is negligible. 30 minutes is sufficient for starch conversion, but even if you pull a third of the wort out, you still have your grains mashing away at 1:1 while the decoction is taking place. Getting a few gallons of ~154 liquid up to a boil takes about fifteen minutes (depending on your heat source) and then I let it boil for another fifteen. Once the decocted portion is back in, I stir and let the grain bed settle for ten before I begin the Vorlauf and lauter. There you have it, an easy, no fuss method to achieve maltier, clearer and more efficient beers.