Shorten your brew day with overnight mashing

by Brewing beer

You’ll often hear all-grain brewing takes around four hours minimum, but I’ve seen bad brew days extend as much as 7 hours (it was cold, and many, many things went wrong).  I’ve found breaking the brew day into two days helps improve brewing enjoyment and keeps me sane.

The Overnight Mash

It doesn’t matter how you all-grain brew, you can overnight mash if you batch sparge or continuous sparge.  The idea is to mash your grains overnight in a cooler.  That’s it.  Start your mash and then go to bed.  The next morning you can pick up brewing right where you left off.

mash tun cooler

You'll need a cooler like this one to hold your temperature overnight. Make sure you test it before committing grains to it.

I sometimes alter the process by starting the mash early in the morning, and then pick back up later in the afternoon.  The “overnight mash” really should be called an extended mash.  The only problem with this method is you need to start very early or brew late.  This kinda defeats the whole point of making the brew day shorter, but it can give you time to run errands in between the mash and the boil.

The overnight/extended mash will have the same effect as a 90-minute mash.  The mash efficiency might actually be a bit better, but you do no need to worry about dramatically increasing your attenuation.  Your starting temperature determines the fermentability.

I usually start my mash in the evening after dinner.  If you are brewing in a colder area, you’ll want to bring your cooler inside and put a blanket around it.  This will help your mash maintain temperature overnight.

  • Mashing overnight splits the brew day into two smaller sessions
  • Once the starches are converted, the mash is just occupying space until you start your brew.

Watch your temperatures

Your cooler should hold temperature as close as possible to your target mashing temperature, especially for the first two hours of your mash.  This is the time period when your starches are converted to sugars.  During the first few hours the amylase (enzymes which break down starches to sugars) do their work.  Once they are done, your mash is just hot sugar tea ready for boil.

Leaving the mash overnight will not affect the attenuation, even if you are targeting a lower fermentable mash.  The reason is at 150 F the amylase will denature within the normal mash time.  After a few hours, there will be no amylase left.  Everything that is going to happen happens in the first two hours.  Losing temperature after this point will not affect your wort’s attenuation, but it may cause other headaches for you.

Holding your temperature is important if you are continuous sparging.  If the temperature gets too low, you won’t be able to dissolve the sugars in your grain bed and you’ll get a lower efficiency than planned.  To avoid this situation, you should do a mash-out.  The mashout is raising the temperature of your mash to 170 F prior to lautering.  This will help dissolve the sugars and improve your efficiency.  This problem is avoided in batch sparging the same way when you add your strike water.

Another concern is a bacterial infection.  If your temperature drops below 130 F, your wort might be susceptible to a bacterial infection.  The bacteria will be killed off in your boil; however it might produce off-flavors before the boil.  I’ve never had this happen because I’ve never had my temperature drop below 145 F.  Your mileage may vary, however even if your temperatures go below 130 F the risk is low.

Temperatures are important, but don’t stress so much that you are checking the temperature all night.  Check the temperature the next morning when you start your sparge or boil.  The morning temperature will tell you if you should add blankets to the cooler next time, or sleep easy through the night.

  • A mash-out may be required if you continuous sparge
  • Most bacteria will die off in temperatures over 140 F, but if you go below 130 F you might get off-flavors
  • Requires more planning and fore-thought

Proper Equipment

I use a Coleman Extreme 5-day cooler for my mashes.  The cooler lid sits inside the cooler and the whole thing is heavily insulated.  I’ve had great success maintaining temperatures overnight with this cooler.  Even in the cooler months of the year the cooler holds the temperature well; however this cooler is best suited for batch sparging.

mash tun

Keep a thermometer in the mash tun so you can make sure your mash tun stays on temperature

You could use any cooler, but you might need to “supplement” the insulation with blankets.  If you are using buckets or another mash tun without insulation, you’ll need to use lots of heavy blankets to hold temperature.  You may need to be creative with Styrofoam insulation.  Just try to hold your mash temperature for the first few hours, after that stay above 140 F.

  • 5-day coolers work best for overnight mashes.  In my experience, I lose no more than 5 degrees overnight with a 5-day cooler.
  • The color of the cooler does not matter, but I prefer blue. 😉

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Credits and Links

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DJ Spiess

DJ Spiess

Beer buddy

I live in Denver, Colorado. This blog is everything about beer, wine, cider, mead and other spirits.
I am a avid homebrewer and winemaker. I’ve been making my own beer and wine for many years. I started making beer when I was in college (mostly because the drinking age in the United States is 21). My first few beers were horrible. The beers are much better now, and I often supply my neighborhood with free beer! It is a great hobby!