An Introduction to Partial Mash Brewing

Last time, we were talking about the difference between mashing and steeping your specialty grains.  How to tell which grains can be steeped and which need to be mashed, and why.  So now that we know about the ingredients – let’s take a closer look at the process.

Assuming you’re doing a full wort boil, you likely already have all of the equipment to do a simple partial mash.  In addition to your main brew-pot, you will need:

• A second 2-3 gallon pot to heat your sparge water in.
• A large grain bag (a paint strainer from the hardware store works well too)
• An accurate thermometer.

It’s still just grain and hot water right?

Basically.   The differences are subtle, but very important.  There are 5 things you probably don’t pay that much attention to with steeping that can have a big effect on your mash.

First – Enzymes. As we discussed, these are the little guys that do the work of converting those starches into sugars.  The “base” grains will generally contain enough enzymatic power (also called Diastatic Power) to convert all of their own starches, plus those in the specialty grains.  The higher the kilning temperature the lower the diastatic power of a malt.

Second – Water. If you just fill the pot with the full amount of water – the enzymes can be too diluted and won’t work properly.  Target about 1.5 quarts per pound of grain.  This is about the standard for home brewers – although some commercial breweries go as high as 3 or 4 quarts per pound of grain.

Third – Temperature. Grain contains lots of different enzymes, but the ones we are interested in are active between about 145ºF (60ºC) and 158ºF (70ºC).  Don’t over-do it though – if the temperature range is exceeded the enzymes will begin to denature.  Once they’re gone you can’t get them back.

Fourth – Time. You’re probably used to steeping for about 30 minutes.  Full conversion will take about an hour – so you may need to apply a little heat to keep the temperature steady.

Fifth – the Sparge. With steeping you’re mainly after some color and a little flavor, but now we’re after those sugars as well.  Instead of just lifting the grain bag out of the water and letting it drain, we actually want to rinse it with more hot water to get any remaining sugars out.

Step by Step

Step 1: Put your crushed grain into your large grain bag or paint strainer.  Just like steeping, but you’ll probably need a larger bag.

Step 2: Fill one of your pots with the suggested 1.5 quarts of water per pound of grain that you’ll be mashing.  Don’t put the grain in yet.  Heat to about 155ºF.

Step 3: Add your grain bag.  This will cause the temperature of the water to drop a few degrees so add a little heat to bring it back to about 152ºF.

The enzymes on the lower end of the range promote grater fermentability, at the higher end a less fermentable wort.   This is one ways to adjust the finishing gravity of your beer.  For now, 152ºF is a good middle of the road temperature.

Step 4: Hold this temperature as consistent as you can for the full hour.  Use the lid if your pot has one.  If you add heat from the burner be sure to stir constantly to prevent any scorching.

Step 5: In a second pot heat 2-3 gallons of water to 168ºF (75ºC).

Step 6: After the hour long rest -  remove the grain bag from the first pot, let it drain and then put it into the second pot.  Swirl it around a bit and let the second pot stand for another 10-15 minutes.  Lift the grain bag out of the water and let it drain.

That’s It?

Yep.  That’s it.  Pour the liquid from the smaller pot into the larger one.  Fire up the burner and bring it to a boil.  Continue on with your normal brewday adding the extract which will provide the remaining gravity points and hops as scheduled.

There you have it.  Once you’ve got a handle on partial mash brewing you’ll be able to tackle pretty much any style out there.  There’s no stopping you now!  For some additional reading on the subject check out Brewing Classic Styles (Appendix C) and  How to Brew.

Tagged as: grain, homebrew, introduction, mashing, partial mash, steeping