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Partial mash brewing

A partial mash, also called a mini-mash, is a hybrid between kit or extract brewing, and full mash brewing. A can of concentrate or malt extract is used, and extra fermentable sugars are added by mashing grain to convert the starches to sugar. Hops are often added to supplement the hops in the can of concentrate. Of course, if unhopped extract is used then hops must be added.

Partial mashes are popular for several reasons. First, most people believe that beers made with concentrate or malt extract have a distinctive taste that all-grain beers do not. Doing a partial mash helps mask this flavour and give a less tangy, "homebrew" taste. Second, a partial mash can be done easily with equipment found in most kitchens. Third, it gives a glimpse of the techniques behind full-mash brewing with many of the benefits, but without needing a whole lot of equipment.

Step by step: Partial mash brewing

There are several methods of doing a partial mash. These instructions are based on a post on our forum by Trough Lolly and involve using an insulated Esky (portable cooler) to mash the grains in. A partial mash can also be done in a saucepan on a stovetop, but constant monitoring of the temperature throughout the mash is essential.

To do a partial mash in an Esky You need the following equipment:

  • Two pots/saucepans — a smaller one to heat up the brewing water and a larger one to boil the wort (a 12-litre stock pot is good).
  • An Esky of at least six-pack size, which will be your mash tun.
  • A colander or mesh strainer.
  • A handheld thermometer with a probe (available from kitchen supply or electronics shops).
  • A soup ladle.

Unlike when steeping specialty grain, temperature control is important when doing a partial mash. The key to a good mash is being able to hit the right temperature at the start of the mash. A good temperature to mash is 66C, and once you have mastered the process you can adjust it up or down, to make a fuller-bodied or drier beer, respectively. The temperature of the mash will determine which of the enzymes that convert starch to sugar will have the most influence on your mash — a mash between 60 to 65C will result in a more fermentable, dryer beer whereas a mash between 65C and 70C will deliver a more malty and fuller-tasting beer. A good all-round temperature is 66C. For more information on mash temperatures see The brewing process.

To achieve the 66C mash temperature, you need to take into account that your mash tun (the Esky) will absorb some heat, as will the grains when you add them into the mash water. The exact "strike" temperature will vary depending on the equipment and how much grain you are using. For your first effort use water at 74C, and adjust it in future brews so that you hit 66C consistently on your equipment.

Remember that you need "base malts" such as ale malt or pilsner malt to do a mash. These grains have been malted and are ready to be mashed, during which the enzymes in them will convert the grain's starch fermentable sugars. Specialty grain such as dark malts and crystal malt contain no starches that can be converted to sugar during mashing. While specialty grain can be and usually is added to the mash along with the base malts, nothing is extracted from them by mashing that wouldn't be extracted by steeping.

Also, the grain must be crushed before it can be mashed. It only needs to be cracked open to allow water to get inside the grain easily. Your homebrew store can crush the grain for you. Make sure your ask them to do it when you order your grain because otherwise they may assume you intend to crush it yourself.

Here is how to do a partial mash in an Esky:

  1. Work out how much water you will need for the mash. Use at least 2.3 litres of water per kilogram of grain.
  2. In the smaller saucepan heat the water to 74C, measuring the temperature with the thermometer.
  3. Pour the water into the mash tun (your Esky).
  4. Gradually pour in all of the crushed grains, stirring gently as you go to make sure there are no balls of dry grain. This process is called "doughing in".
  5. The mixture should be at least as thin as a soft porridge.
  6. Measure the temperature. Add some boiling or cold water if it is not around the 66C mark. It's not the end of the world if you are a degree or two either side — the mash will still work.
  7. Put the lid on the mash tun and let it sit for 60 minutes. Every 15 minutes stir it and check the temperature. The temperature will drop a little over the hour, but generally don't worry about this because conversion still occurs unless you get below about 60C. If the temperature does fall more than a couple of degrees, add a cup of near-boiling water and stir it in well. This should raise the temperature sufficiently.
  8. While the grain is mashing, prepare the rest of the equipment and ingredients you're going to use.
  9. As you near the end of the one-hour mash, heat about 3 litres of water to 75C in the smaller pot. This will be the sparge water that's used to rinse the grain.
  10. Place a colander or fine sieve over the larger pot.
  11. Ladle a few scoops of the grain from the mash tun into the colander.
  12. Slowly and gently pour a cup or so of the 75C hot sparge water over the grains to rinse out the last of the sweet liquor.
  13. Keep adding grain to the colander and rinsing it until all the grain has been rinsed. If you have any sparge water left over, continue rinsing the grain gently.
  14. Eventually you should have collected about four or five litres of sweet liquid.
  15. Discard the "spent" grain.
  16. Bring the liquid to the boil and simmer it for five minutes.
  17. Use the liquid to boil or steep any hops, then mix in the rest of the ingredients such as malt extract or tin of concentrate.
  18. Cool the liquid by placing the saucepan, covered, into a sink of cold water for 15 minutes, stirring both the wort and the cold water occasionally.
  19. Continue brewing as usual.

When doing a partial mash there is no need to sanitise anything that is going to be boiled. From the time you begin to cool the wort, sanitation becomes essential  because it's from this point on the wort becomes an attractive breeding place for microbes because it is both a great source of food and an ideal temperature for the microbes.

Having mastered partial mash brewing, you will probably begin to wonder why you don't make the next step, to all-grain brewing.

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