Brew Day Hour 1: Mash the Grains

Brew Day Hour 1: Mash the Grains

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Emma Christensen
May 12, 2015
(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today's topic: Detailed look at the mash step of brewing beer
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Every batch of all-grain beer starts right here, with the mash. This is where we take the dry, cracked grains, combine them with some warm water, and make the malty, sugar-filled liquid that will be the base for our homebrew. And it's really not much more complicated than making an extra-large batch of oatmeal or cooking a pot of pasta. If you can handle those kitchen tasks, then you can handle mashing grains to make beer.

Here's everything you need to know about the first hour of your brew day.

Don't forget to crush your grains before brewing with them.
(Image credit: Melissa Ryan)

Talk Like a Brewer

  • Strike Water: The water mixed with grains to make the mash.
  • Strike Temperature: The temperature of the water before the grains are added; it's specifically calculated so that, after adding the grains, the temperature evens out to the proper mash temperature.
(Image credit: Henry Chen)

What Happens During This Hour?

The mash is just what it sounds like: mixing grains and water to make a porridge-like mash. What makes this different than just mixing up a batch of oatmeal is the ratio of water to grains, and the temperature. I prefer a ratio of 1 1/2 quarts of water to 1 pound of grains, which I've found works best for certain enzymatic reactions in 1-gallon batches and also makes the next step, sparging, a little easier.

For most ales, the ideal temperature of the mash is 148°F to 153°F. Try to keep your mash in this range for the whole hour of the mash. I find that putting the covered pot in a warm oven does a great job at keeping the temperature fairly steady. If you check the temperature and it's a little high, stir the mash until the temperature comes down; if it's a little low, put it directly on the stovetop for a minute or two.

Also, know that you have a roughly 10-degree buffer on either side where conditions are less ideal, but you don't need to worry that you've ruined your beer. Even then, if you go outside the buffer zone, you might notice bitter flavors or have low alcohol levels, but the beer itself will still be good.

(Image credit: Melissa Ryan)

Why Is Mashing Important?

Though it might look like nothing more exciting than watery porridge, there are some important things going on in the brew pot during this hour. Starches inside the grains are dissolving into the water. Once there, two different enzymes (which rode in on the grains and were activated by the warm, wet environment) get to work breaking the starches down into simpler sugars. These sugars become yeast food, so we want to make sure conditions are perfect for the enzymes to do their job.

One of the enzymes, alpha-amylase, works best at warmer temperatures, and the other enzyme, beta-amylase, works best at cooler temperatures. To get the most out of both of them, we aim to keep the temperature of the mash at a happy median between the two — 148°F to 153°F.

The length of the mash step is also important. It takes the enzymes about an hour to completely convert all the starches into sugars, so be sure to let the mash go for the full 60 minutes. If you had some trouble with high or low temperatures, you can add on an extra 15 to 30 minutes to make sure you've given the enzymes enough time to finish up.

(Image credit: Melissa Ryan)

What to Do: Mashing the Grains

These general directions apply to any batch of beer you brew. Your specific recipe should tell you how much water to use, though if you need to, you can also calculate it yourself using a ratio of 1 1/2 quarts of water for every pound of grains.

Flip through the slideshow above for step-by-step photographs of each step of the mash process.

Before you begin your brew day:

Take liquid yeast out of the fridge and set it on the counter to warm up. Some pouches may need to be activated before using, so carefully read through the directions on your package. Dry yeast does not need to be warmed or activated.

  1. Heat the oven for 5 minutes and then turn it off: The oven is an ideal incubator for the mash. It helps hold the temperature of the mash very steady, often for the entire hour-long mash period. Heat it just for 5 minutes (or until an oven thermometer reads 170°F) with a rack on the lowest shelf, and then turn it off.
  2. Measure the water: Use a liquid measuring cup to measure the water and be as accurate as you can. This said, if you're off a little bit, your mash will be fine. Pour the water into a large pot — ideally, your pot should be 12 quarts, but you can brew in a pot as small as 8 quarts.
  3. Warm the water to 160°F: In brewing terms, this is called your "strike water" and the temperature is the "strike temperature." The temperature is calculated specifically so that, once you add the grains, the mash will even out to the correct mashing temperature.
  4. Stir in the grains: Off the heat, pour all the crushed grains into the water and stir until you have a porridge-like consistency. Check the temperature — it should be 148°F to 153°F. If it's a little warm, continue stirring until the temperature falls below 153°F. If it's a little cool, put the pot back on the heat for 1 minute, stirring gently and monitoring the temperature.
  5. Place the pot in the oven: Cover the pot containing the mash and place it in the oven with the door closed.
  6. Check the temperature every 15 minutes: Every 15 minutes, take the pot out of the oven, stir the mash for a few seconds to get rid of any hot spots, and check the temperature. If it's a little warm, continue stirring until the temperature falls below 153°F. If it's a little cool, put the pot back on the heat for 1 minute, stirring gently and monitoring the temperature.
  7. After an hour, the mash is finished: At the end of the mash, the liquid should taste very sweet, smell malty, and look darker-colored. If you had trouble with high or low temperatures, you can mash for an extra 15 minutes to make sure you've extracted all the sugars you can.
  8. Taste the mash: Go ahead, give it a taste! It should taste very sweet and a bit grainy — don't worry, it will start tasting like real beer in the next few weeks.

You're finished with the mash step, and ready to move on to sparging!

(Image credit: Melissa Ryan)

Troubleshooting the Mash

I can't get the temperature of my mash to hold steady — it shoots up and then drops down.

The thick, porridge-like mash often develops hot spots, especially as the grains settle to the bottom of the pot or as the pot sits over a burner. Stir the mash gently for a few seconds before checking the temperature to be sure you're getting an accurate reading. When warming the mash on the stovetop, only warm it for a minute at a time, then take it off the heat, stir, and check the temperature. It's really easy to overshoot your temperature mark — warming it in intervals helps prevent this from happening.

My mash went over 153°F — is it OK?

Yes! As soon as you notice, stir the mash off the heat to bring it down below 153°F. You might end up with a slightly lower alcohol level and more malty flavors in your finished beer, but your beer will still ferment just fine.

My mash went over 170°F — is it OK?

Temperatures over 170°F effectively stop all enzymatic activity, meaning you can't get more sugar in your beer. If this happened at the very beginning or end of your mash and you brought the temperature down as quickly as you could, the beer should be fine. (Also, beers often form hot spots as they warm — stir the mash for a few seconds before checking the temperature for the most accurate reading.) If it was definitely above 170°F for more than a few minutes, though, you might not have enough sugars to ferment the beer. Taste the wort — if it tastes sugary to you, then your beer is probably fine. But if it tastes like starchy water, then best to ditch this batch and start again. Better luck next time!

My mash went under 148°F — is it OK?

Yes! Put it on the heat for just a minute, stirring gently and checking the temperature. Take it off the heat as soon as it hits 150°F (it will continue to rise a degree or two after you take it off the heat). If it was below 148°F for a long time, you may end up with a thinner-bodied beer with a slightly higher alcohol level than expected, but your beer will ferment just fine.

My mash went under 140°F — is it OK?

Yes! See above, and then mash for an extra 15 to 30 minutes to make sure you get enough fermentable sugars in your wort.

Brew Better Beer: A Companion to Beer School

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I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

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