Introduction to Partial Mash Brewing

Whether you’re a novice home-brewer who has outgrown kits and all-extract limitations, or a long-time brewer looking for an easier day brewing, the partial-mash technique of brewing has several merits worth exploring. It is considerably less time- and labor-intensive than all-grain brewing, requiring fewer steps and less cleaning.

Process-wise, partial-mash brewing most closely resembles extract brewing, and is a good intermediate step before going all grain. With partial mash brewing, some of the fermentable sugars come from mashed grains, and the rest from extract. The introduction of a more natural mash process using fresh ingredients translates into higher quality beer. The added control also allows for a boarder variety of styles and control.

The transition from all-extract to partial-mash brewing is fairly simple. In terms of hardware all that is needed extra are a strainer or grain bag, a floating thermometer, and an extra cook pot. In terms of brewing, it is just one additional step called mashing.

Mashing is simply the process of converting the starches in grains to sugars. All it takes is crushing the grain, and steeping it for an hour at 150F. The husks are then separated from the wort that is left behind, and the boil proceeds as normal.

The Process:

First the grains need to be crushed lightly. The goal is to crack the exterior shell of the grain, allowing the hot wort to convert the starches and proteins inside into sugars and non-fermentables for flavor. Most brew stores can crush your grains for you, or you can do it yourself with a rolling pin or similar instrument; if you decide to crush your own, remember that the goal is to crack the shell, not grind into powder. The best way to do it is with a grain mill attached to a cordless drill. Corn style mills called corona mills can be used as well. Make sure to crush the grains within 24 hours of brewing.

Start by heating 2 gallons of water to 170F in a 5 gallon pot. The reason the water is heated to 170F is when the room temperature grains hit the water the temperate will drop. 150-155F is the standard mashing temperature you are shooting for. When the water is ready, called the ‘strike water’, add the crushed grains to a bag and submerge. Make sure to gently stir the crushed grains so there are no dough balls. Cover the pot, and let sit for an hour. Monitor the temperature every 10-15 minutes for fluctuations and either increase or decrease the heat accordingly – do not let it boil!

At this point start preparing an additional 2 gallons of water at 175F. This will be your sparge water, used to strain the reaming sugars from the grain bag. You should have a really nice sweet smell emanating from the pot. After an hour, the partial mash is completed. The spent grains should be separated from the wort. Once separated, the grains should be sparged (washed with water) to remove as much of the converted sugars and non-fermentables as possible. When washing and pressing the grain, be as gentle as possible; the goal is not to further crush your grain, (which can add grist to your wort) but merely to wash and press out the converted wort.

Now you have your very own sweet wort you mashed yourself! Fire up the kettle and proceed as normal like you do for an extract batch. You will need less malt extract because you created some of the fermentables during the mash. The recipe should guide you to the correct amounts already.

Other thoughts:

There is some debate between home brewers as to ideal method of mashing the adjunct grains. One method is to add the grains to the extract as it comes to a boil, and allow the grains to boil with the wort. This method allows the grains to fully mash, but because of the high heat of the boil, a lot of the tannins in the grain enter the wort as well, giving it a more astringent or dry flavor, and leading to a chill haze in the finished beer. Chill haze is an aesthetic issue, but the grainy tannic flavor can be a serious negative depending on the brew. In pale ales and bitters, you may not notice, or may even find it a plus, while in sweeter beers such as bocks and browns, the dryness may be in strong (and unpleasant) contrast to the base flavors.

There are tools available online to convert between all grain and partial-mash recipes, letting brewers move up from extract brewing to partial mash at their own comfort level and experiment with more varied recipes. For exceptionally sweet or high-gravity beers, it may be easier to use a partial-mash approach; my brewing group’s attempt at an 17% ABV beer would have used almost 30 lbs of grain; by replacing the base malt with an extract, we saved ourselves several gallons of water and several hours of reducing the wort. For all-extract brewers, partial-mash lets them tinker with their tested recipes; the difference between a Porter and a Smoked Porter may be as little as half a pound of peat-smoked grain, and a dopplebock might get a nice biscuit flavor from a pound of Belgian Special B grain.