Partial mash brewing for kit homebrew

Partial mash brewing will take your extract kit beers to the next level.

Through adding a small amount of crushed malted barley and some specialty malt, your homebrew can be comparable to your favorite craft beer.

There is a bit of science, but essentially you are making porridge-like mixture, leaving it for an hour and then boiling the liquid.

Explaining mash conversion with a dinner time analogy

It’s not important that you understand the science behind mashing, but let me try to explain it through an analogy...

Imagine trying to serve up a sack of potatoes to your kids for dinner.

Their little fingers can’t open the sack. The potatoes are too big and hard. They are raw so, not surprisingly, your kids don’t eat them.

So you take the potatoes to the kitchen. Open the bag, peel them, chop them up, coat them with a little oil and salt. Roast them in the oven for a while.

The potatoes are now chips and everyone loves them.

It’s empty plates and smiles all around.

Sack = malt grain kernel.

Opening sack = crushing the grain.

Potatoes = starch molecules.

Kids = yeast.

You = enzymes.

Cooking = mashing.

Chips = fermentable sugars and flavors.

I guess a happy household would be the resulting beer, but I think we can pull it up here.

Back to homebrewing...

This conversion step is really important when brewing with malted grain.

Your yeast can’t eat starch, so you need to break it down into something more palatable (ie simple sugars).

You don’t need to understand the science, just follow the following guidelines and your beer will be awesome.

pH pointers

Brewing enzymes work best at a pH of 5.3, but this is not something you need to worry about too much.

You can avoid pH problems by:

  • Adding any dark roasted specialty grains after the main conversion mash has taken place.

  • Adding a little gypsum (calcium sulfate) to mash when mixing in. Use half a teaspoon per 4.5 pounds (2 kg) of grain.

  • Use soft/neutral water.

Gear needed for partial mash brewing

You don’t need much gear for mashing grain. All you need is a:

  • Large pot and lid (3 gal/12 L or more).

  • Large grain bag (when open, the bag’s circumference is slightly than your pot).

  • Large colander.

  • Thermometer.

The pot and grain bag in action.

The pot and grain bag in action.

The colander sits in the mouth of the pot and drains the sugary liquid from the grain.

The colander sits in the mouth of the pot and drains the sugary liquid from the grain.

Partial mash brewing in three parts

#1 – The mash

Gently mix your crushed grain into your hot water.

Gently mix your crushed grain into your hot water.

Once your mash temperature is close to target, seal with lid and move to your pre-warmed oven.

Once your mash temperature is close to target, seal with lid and move to your pre-warmed oven.

  1. Heat two gallons (8 L) of water in your pot to around 162°F (72°C).

  2. Remove the racks from your oven and heat to approximately 153°F (67°C).

  3. Sit your grain bag in your pot and secure around the outside of the rim with string or a large rubber band.

  4. Gently and gradually mix your grain into the hot water. Keep any dark specialty grain aside for now.

  5. Optional: mix in half a teaspoon of gypsum (calcium sulfate). This will help with mash pH.

  6. Check the mash temperature and adjust to 153°F (67°C) with heat or cold water if needed.

  7. Cover the pot and move into the oven.

  8. Leave for 60 to 90 minutes.

#2 – Steeping and sparging

After the main mash has taken place, heat to 171°F (77°C ) and stir in any specialty malt.

After the main mash has taken place, heat to 171°F (77°C ) and stir in any specialty malt.

After 15 minutes lift up the grain bag and sit in the colander.

After 15 minutes lift up the grain bag and sit in the colander.

Gently pour hot 171°F (77°C) over the grain bed to rinse out remaining sugars.

Gently pour hot 171°F (77°C) over the grain bed to rinse out remaining sugars.

  1. Move the pot back to the burner and turn on the heat, stirring gently.*

  2. Once it hits 171°F (77°C), turn off the heat.

  3. Stir any specialty grain, seal and leave to steep for 15 minutes.

  4. Wearing gloves, gently lift the bag up and hold above the pot.

  5. When you get tired of this or most of the liquid drains out, place the colander in the pot mouth and sit the grain bag in it

  6. Gently pour half a gallon (2 L) of warm (171°F/77°C) water over the grain bag to wash out some of the remaining sugars.

*Note: If you want to save time heating the mash, pre-boil two quarts (liters) of water and mix in with the specialty malt.

This will push up the mash temperature and help extract extra maltly goodness. There is no need to rinse/sparge the grain bed if you do this (ie don’t follow step 6).

#3 – The boil begins

Boiling the malt liquid is essential to destroy any microbes, develop malt flavors and extract hop profile.

Since we are getting base bitterness from the pre-hopped kit, we only need to add any flavoring and aroma hops additions.

Scoop off any brown foam.

Scoop off any brown foam.

Add hops and whirlfloc as per your recipe.

Add hops and whirlfloc as per your recipe.

When the boil is finished, turn off the heat and dissolve in your malt extract.

When the boil is finished, turn off the heat and dissolve in your malt extract.

  1. Turn on the heat and watch carefully. It will try to boil over a few times when the boil begins.

  2. Scoop off any brown foam with a slotted spoon. This is grain flour and will hurt your beer flavor.

  3. After boiling for 45 minutes, add any flavoring hops and a third of a whirlfloc tablet.

  4. Boil for another 15 minutes and add any aromatic hops.

  5. Boil for one more minute, turn off the heat and mix in your homebrew tin and any extra malt extract.

  6. Cover with the lid and seal up with plastic wrap. Move to sink filled with ice water to cool.

  7. Fill your cleaned and sanitized fermenter with four gallons (15 L) of cold water and seal.

  8. When the side of the brewpot feels cool to touch, gently pour the wort into your fermenter, leaving most of the sludge behind.

  9. Mix, pitch your yeast and seal. From here it is business as usual to ferment and bottle/keg.

Partial mash brewing tips

Mash at 153°F (6 7°C) for 60 minutes

As we covered earlier, enzymes in the grain will transform starch into sweet fermentable sugar at this temperature and time.

Lower (147°F or 64°C) will give a drier, more fermentable beer.

Higher (156°F or 69°C) will give you a sweeter, full-bodied beer.

Close enough can be good enough

If your mash temperature is close to your target (ie within 149-155°F or 65-69°C), this will still give great beer.

Often it is a lot of work to adjust a few degrees that will have marginal impact on your final beer.

It’s hot and sticky

You are handling a large amount of boiling hot wort so wear gloves, pants and covered shoes.

Also, wort is really sticky. Unless you watch your pot carefully, it can quickly boilover and create a mess.

Stopping boilovers

Have a spray bottle filled with cold water. If you spray the boiling pot a few times, boilovers will stop in their tracks.

You won’t have a great sugar extraction rate

All grain brewers extract anywhere from 60-80% of the grain’s available sugar through advanced gear and techniques.

We are simplifying things here, so will be far less efficient.

In recipe design, estimate an extraction rate of around 55%. Keep a pound (440 g) of dry malt extract handy in case you need to top up your fermentables.

Clean and sanitize (more!)

You are putting extra time and effort into brewing with grains, so don’t waste this with an infection.

Make sure you follow a solid cleaning and sanitizing regime.

Mix the crushed grain in completely

Make sure you break up any dry balls of malt. The mixture should be completely wet or the beer will end up starchy and unstable.

Don’t aerate your mash or hot wort

Oxygen is a bad thing if your mash or wort is above 80°F (27°C). It makes your beer stale more quickly.

Don’t heat your grain too much

If your wet grain gets over 170°F (77°C), you will extract tannins and other compounds which aren’t great.

Get a good rolling boil

Vigorously boil the sugary malt solution for an hour or more. The boiling action will give you stronger flavors and more stable beer.

Cool quickly

There are processes happening in hot wort. The longer they continue after the boil, the more likely your beer will taste a little odd.

Also cooling rapidly causes proteins (cold break) to drop out more quickly. It also minimizes the chance of infection.

Aerate your cool wort

If you are boiling more than half of your final wort volume, so you may need to aerate your wort when it cools below 80°F (27°C). Using a fresh dry yeast will usually counter this need, as it comes packed with excess resources.

However if you find fermentation is sluggish, you may need to aerate the wort.

There are many ways to do this, but frothing wort violently in the fermenter with a large sanitized spoon or whisk is the simplest.

Add any dark specialty grains after the main mash

Dark grains can affect your mash pH, which is really important during the mash conversion process.

If your recipe calls for dark specialty grain such as roasted malt, dark crystal or patent malt, add these after the one-hour main mash.

Raise the mash temperature to 170°F (77°C), mix in the specialty grains and let it sit for 20 minutes for the grain profile to steep out.


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