I’m a big fan of partial mashing. For all-grain brewers who usually brew outside, it allows you to get out of the elements during inclement weather and brew in your kitchen. For extract brewers, there are a host of benefits.
Adding base malts to your extract recipes increases the aroma of base malt, which is sometimes lacking in malt extracts. And, it allows you to use the many different kinds of base malts out there and base malts made by different maltsters. More ingredients to choose from gives you the opportunity to more finely tweak the flavor of your beers.
A partial mash also allows you brew a lighter-colored beer, compared to the extract-plus-steeping-grains method, if you want to. In addition, if you’re trying to make a dry beer, you can use the enzymes from the partial mash to raise the fermentability of your wort. Finally, you can add small amounts of starchy adjuncts to your beer, without having it turn hazy. Starchy adjuncts include flaked (or torrified) unmalted grains such as flaked maize, flaked barley, flaked wheat, torrified wheat, rolled oats, etc. [The weight of the starchy adjuncts should be 30% or less of the total weight of the grains, excluding any malt extract, and paired with a lightly-kilned base malt with plenty of diastatic power (enzymes to convert starches) such as US 2-row pale malt or US 6-row pale malt.]
A small partial mash can be accomplished almost exactly as you would brew an extract recipe with steeping grains. The only procedural difference is you need to watch the temperature more closely and not “steep” the grains in too much water. It’s hard to think of any drawbacks to the method, although you might generate slightly more break material in your brewpot.
Mashing vs. Steeping
When specialty grains are steeped, the color and flavors from their husks are dissolved into the water. Likewise, any sugars from the interior of the grains are also dissolved. If a grain has a starchy interior, it should be mashed rather than steeped. (See the list that accompanies this article for grains that should be mashed.)
You can steep specialty grains and almost any temperature, from the temperature of your water right out of the tap to nearly boiling. To be safe, it’s probably best not to let your steeping temperature climb above 170 ° (77 °C), especially when you’re steeping a small amount of grain in a relatively large volume of water. This may extract excess tannins and give your beer a slight iced-tea-like character.
Likewise, you can steep specialty grains in almost any reasonable volume of water, up to your pre-boil wort volume. Some sources caution against extremely dilute steeps (for example, less than a pound (0.45 kg) of grains in 5.0 gallons (19 L) of water), as there is the potential to extract excessive amounts of tannin for the grains. However, when steeping specialty grains for stovetop brews of less than 3 gallons (11 L), you are unlikely to run into any problems.
When base grains — or a mixture of base grains and specialty grains — are mashed, the temperature is usually held between 148 °F and 162 °F (64–72 °C). Lower temperatures within this range and longer mash times (60–90 minutes) produce wort with a high degree of fermentability. Higher temperatures within this range and shorter mash times (ending when an iodine test shows a negative result), followed by a mash out, make worts with a lower degree of fermentability. A mash out is a step in which the grains are heated, by direct heat or by adding hot water, to 168–170 °F (76–77 °C) after then mash. (There are more complex mash programs, such as step mashing and decoction, but partial mash recipes rarely call for these. Almost all partial mash recipes call for a single infusion mash.)
Likewise, in a mash, the volume of water is limited so that the grains make something similar to a porridge. Generally, the mash thickness varies between 1.0 and 2.5 quarts of water per pound of grain (2.1–-5.2 L/kg). A mash thickness of 1.25 qts.lb. (2.6 L/kg) is frequently used in homebrewing as it is fairly thick and therefore you can mash a lot of grains in a relatively small volume. Thinner mashes are often used when the mash needs to be stirred, or for decoction mashing. For most partial mash procedures, anywhere within this range will work. I usually mash at 1.375 qts./lb. (2.9 L/kg) in a partial mash, because this allows me to stir the grains easily when they are enclosed in a steeping bag.
So, from a procedural standpoint, steeping and mashing both involve soaking crushed grains in water. When mashing, you simply have a more narrow range of temperatures and grain-to-water ratios to work within. Converting extract recipes to partial mash is simple therefore almost always worth your while. Almost all of the extract recipes presented on this website are partial mashes.
Malts that Should be Mashed (Base Malts)
These malts are mostly lightly kilned (with brown malt as an exception), contain starchy interiors and sufficient enzymes to (at a minimum) convert their own starches into sugars.
2-row pale malt — this can come from the US, UK, Scottland, Belgium, Australia or other countries, and may sometimes be labeled with the name of the malting barley variety (Maris Otter, Golden Promise or Optic)
2-row brewers malt
2-row pale ale malt
2-row lager malt
6-row pale malt
6-row brewers malt
rauchmalz (smoked malt)
mild ale malt
some dextrin malts
Malts That Can be Steeped (Specialty Grains)
These malts do not have starchy interiors, either because the starches have been converted to sugars (in the case of stewed malts) or degraded by roasting. These malts can be steeped or mixed with base grains and mashed.
Stewed malts — including crystal malts, (most) caramel malts, most Cara[Something] malts, including Briess CaraPils (but not every dextrin-type malt), Special B malts
Roasted malts (and grains) — including black malt, chocolate malt, roasted barley, dark wheat malts, Weyermann Carafa malts