Easy Partial Mash Brewing in 7 Steps

You’ve made a few extract-based beer kits, maybe even put together a few recipes of your own. You’re using steeped caramel and roasted malts to add color and flavor to your beer, and everything’s going great. But you want to expand your repertoire, and explore some of the bins of base malts available to homebrewers. Those other bins are full of all kinds great flavors and colors of malts, but base malts need mashing, not just steeping, to get the sugar and flavor out of the kernels and into your beer. Mashing activates enzymes, which are naturally present in malt, to break down long starch molecules into short sugar molecules that yeast can eat. There’s a lot of complex chemistry that I am skipping, but the good news is that mashing is just steeping, but with some additional precision. Learning how to do a partial mash is a giant step toward all-grain brewing, but it’s actually a pretty small step in terms of extra equipment – it’s mostly a change to process.

What you’ll need

• If you’re not already using one, you’ll need a fairly accurate thermometer. Analog or digital will work, so long as you can comfortably tell within a degree or two how hot your water is.
• You’ll also need a grain bag. You’ll use this to hold all of the grain for your batch.
• You can keep using the same pot you’ve brewed in until now, but you may find that a smaller pot will work better, depending on how much grain you’re going to use, the dimensions of the pot, and so on. Try to find a pot that fits your filled grain bag with comfortable room around it. You’ll need another pot of some kind to heat sparge water in – even a teakettle will work, as long as you can check the temperature of the water inside.
• A colander is needed as well – ideally, this will be something you can rest in the top of your kettle to support your grain bag as it drains.
• You’ll need a hydrometer and test jar to see how much of the sugar you’ve extracted from your partial mash.

Process

First, be aware that you won’t be completely replacing malt extract (DME or LME) in your recipes. You’ll need to have enough on hand to make up the difference between what you get from your partial mash and the total gravity contribution needed for the recipe.

1. Crush all of the malt for your recipe and put it in your grain bag. Tie the bag closed. The amount of water you use for the mash is actually important, because too much or too little can affect the pH of the mash. Pour 1.5 to 2 quarts of water into your mashing pot for each pound of grain in your grain bag (3-4 liters per kilogram). Make a written note of how much grain you have and how much water you are using.
2. Next, determine what temperature you will heat the water to. Most mashes will be done at about 152 -155° F (67-68° C), and adding room-temperature grain to the hot water will cause the water to cool down, so we’ll heat the water above this point. A good starting point is about 167° F (75° C). This should get the mash to settle in the middle to the upper end of the desired range.
3. In your second pot or teakettle, heat some water to have on hand in case it is needed for the next step. If it boils, that’s fine – just turn off the heat once it gets there.
4. Heat the water in your mash pot to the temperature to the determined temperature. Turn off the heat and add the grain bag. Make sure to move the grain bag through the water and stir around the bag to equalize the temperature. Make a note (write it down!) of the temperature of the water, both before you added the grain, and after it’s equalized. If it’s in the range of 152 - 155°F (67 - 68°C), you can move to the next step. If the temperature is more than a degree or two outside this range, you can add a hot or cold water, a little at a time, to raise or lower it.
5. Once the mash is at the desired temperature, put the lid on and insulate the pot well. Once easy way to do this is to remove the pot from the stove and to wrap it well on all sides with old blankets or towels. Make sure to get insulate underneath and on top as well, and more layers are better than fewer. Let the mash rest for 45 to 60 minutes to allow the enzymes to work.
6. Just before you declare the mash to be finished, heat some water... about as much as you heated in your mash pot – to 170° F (77° C) in your second pot.
7. Now, unwrap your pot and use tongs or something to lift out the grain bag without using your hands. Put your colander on top of the pot, and the grain bag in the colander. Slowly pour the hot water from your second pot through the grain bag. This is called sparging, and it rinses extra sugars out of the grain and into your beer. You can press the bag a bit to get even more good stuff into your pot.

That’s it! You have successfully done a partial mash.

What's Next?

Now you can measure the volume and specific gravity of the liquor you’ve collected, and calculate how much water and extract you’ll need to add to make your pre-boil wort. For this example, let’s assume you collected 1.5 gallons of liquor at 1.060. We can express that amount of extract by multiplying the gravity points above 1.000 by the total volume. 1.5 times 60 (gravity points) is 90, so we have 90 points of extract in our liquor already. If we are planning to get to a total volume in the fermenter of five gallons, and our target gravity is 1.050, we’re aiming for a total of 250 points of extract, so we will want to add malt extract to make up the 160-point difference.

(50 pts x 5 gallons = 250 pts)

The extract you are using should have a listed value for points per pound – most DME is about 44 points per pound, for example. Since we need to add 160 points to our partial mash liquor, you’d divide 160 by 44 to find that you need about 3.6 pounds of DME to bring the total extract up to 250 points. The water volume is easier to figure – just add water to make your usual pre-boil volume, not forgetting to allow for evaporation and other losses – so if your usual pre-boil volume is 6 gallons, add 4.5 gallons to the liquor from your partial mash. Stir well to make sure that all of your malt extract is dissolved and well-mixed (I find it easiest to do this before turning the heat on, to avoid scorching), then follow your usual process to boil, cool, and ferment the batch. It’s also worth noting that partial mashes do not necessarily have to be done as full-volume boils. If you usually do a concentrated boil to make three gallons of wort and add two gallons of water in the fermenter, that’s still possible – that 4.5 gallons just gets split, with 2 gallons going into the fermenter and the other 2.5 gallons in the boil.

Making Adjustments  To Your Partial Mash For Next Time

Because you were so careful to write down your grain:water ratio and the temperature of the water before and after you added the crushed grain, you have a pretty good idea of how much the temperature will drop for your next batch. If you had to add hot or cold water to get to the right temperature, you can heat the water a little more or a little less next time. Good notes every time you brew will help you with repeat-ability, so that when you hone a recipe to perfection, you’ll be able to brew it again, over and over.

Optional upgrades

If you already had one, a sous vide circulator would make setting and holding the temperature of your partial mash very easy. I don’t think I would spend the money for this purpose alone, though. A refractometer would make checking the gravity of your mash runnings much faster and easier – and it’s such a useful brewing tool in general that I actually do suggest one to all brewers who brew more than occasionally.

Think About Moving to Full All Grain Brewing

The process of partial mashing is exactly the same as Brew-in- a-Bag (BIAB), except for matters related to scale. Once you get this process working well, it’s fairly easy to step up a notch and make all-grain beer. Even if you decide not to make that leap anytime soon, though, partial-mash brewing should significantly open up your recipe-creation horizons. There are a lot of bins to get through at your favorite shop, after all, and that means a really large number of ways to combine all those grains into wonderful things.

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