Missed Your Mash Temp? Don’t Panic. Here’s How to Fix It.

by Todd Hamm | Updated: March 11, 2016

Low Mash Temp

Just as Steph Curry will occasionally botch a 3-pointer, you will occasionally botch a mash in.

Whether it’s from a miscalculation, a cold mash tun or other outside factors, it happens to us all!

A few weeks ago, I had some friends over for a brew day. As the strike water heated up, we cracked open some brewskis and played a few songs on Rock Band. This was going to be a great day!

I mashed in at 163F with a target temp of 152F. The thermometer needle was creeping up, but slowly… too slowly. To my dismay, the mash temp capped out 15 degrees below target.

“Son of a biscuit… I forgot to preheat the mash tun!”

As I stood there in denial staring at the thermometer, I began to think of the implications of my forgetfulness. Will this giant bowl of porridge produce anything usable? If so, how will this affect the outcome of my beer?

Why your mash temp matters

The bad news is that it will likely affect the outcome of your beer. The good news is it’s probably not as bad as you think, and you can mitigate the effects by taking swift action.

We’ll get to the swift action in just a moment.

First, know that the normal mashing temperature range is 145 – 158F (63 – 70C). In general, mashing at the higher end of that range produces longer sugars which are harder for the yeast to eat. More sugar will be left over after fermentation resulting in a more full-bodied beer.

Mashing at the lower end of the range produces shorter sugars, which the yeast will gobble right up. This leaves behind a thinner, drier beer.

Mash too much lower than that and you’ll end up with poor starch conversion and a really thin, “watery” beer.

You’ll also start breaking down precious proteins needed for head retention.  On the other hand, if you mash too high (168-170F), you’ll run the risk of permanently killing the conversion process.

But don’t rage-throw your mash tun into the yard just yet – we can fix it!

What to do if your mash temp is too low

Here are a few options to consider:

Add hot water

Boil a small pot of water and slowly add it to the mash, stirring as you pour until you reach your target temp.

Adding Boiling Water to Mash

If you don’t have any fancy equipment, this is your best bet.

The big thing to keep in mind here is that you are adding volume to the mash. You should take note of the amount of water you are adding so you can make any necessary adjustments to your calculations.

Tools like this Mash Infusion Calculator, will calculate exactly how much water you need to add based on your current mash conditions and the target temperature.

Some brewers will subtract the calculated volume from the sparge water volume to make sure they aren’t adding to the total volume.

Heat the mash directly

Applying Direct Heat

This is a great option if you’re mashing in a kettle because you won’t need to add any water. Just turn on the heat and stir.

Don’t crank the heat, though, or else you might scorch the wort at the bottom.

You can vorlauf to help avoid scorching. Grab a pot or pitcher, slowly drain the kettle into the pot and then pour it back on top of the mash. This will heat the mash more evenly too.

If you’re rocking a RIMS or HERMS, you already know what to do.

For the unacquainted, these equipment setups utilize a pump to recirculate the wort. Mob Barley wrote a great article about RIMS/HERMS. You can also check out Billy’s Brutus 10 build to see exactly what it takes to build a top-notch automated homebrew system.

A more exotic (and dangerous) method is the use of a heat stick. A heat stick is typically a modified water heater element you hold in your hand. You can buy pre-made heat sticks online, or take the DIY option if you’re feeling extra brave and adventurous.

Heating elements are extremely hot and must be submerged at all times while in use. These things are capable of boiling water fairly quickly, so you must be very cautious and constantly stir with the heat stick to avoid scorching the grains.

I know a guy who built his own and he swears by it!

Perform a decoction mash step

Decoction Mash

This might take a little longer and require more effort, but this might be a good option if your kettle is available.

Pull a portion of the mash out (usually around 1/3 of the total mash) and gently bring to a boil in a separate pot. Make sure to stir frequently to avoid scorching. As soon as the mash starts to boil, return it to the mash tun, stir, and check the temperature.

What to do if your mash temp is too high

In general, this is an easier problem to fix. You don’t need any fancy equipment, and it usually doesn’t take as long to reach the target temperature.

Add cold water

Adding Cold Water

Just as you would add boiling water to raise the mash temp, you can add cold water to the mash to cool it down. The tools mentioned above (Beersmith, Brewtoad, etc.) will also tell you how much cold water to add if your mash temp is too high. Just as before, you’ll want to take note of how much water you’re adding so you can update the water/grist ratio.

Add ice cubes

Ice Cubes

Ice cubes will lower the mash temp faster and with less water. Drop a few in and stir well.

Just be careful not to drop the temp too much. You only need a handful.

Use frozen containers


Some brewers keep a small arsenal of frozen containers (gel packs, ice packs, frozen water bottles, etc.) handy for things like ice baths or swamp cooler fermentations. Toss a few of these into the mash and stir as if they were ice cubes.

Frozen containers are easier to scoop out when you reach the target temp, ensuring you don’t over cool the mash. Plus, you’re not adding any volume.

Use a wort chiller

Wort Chiller

If you’ve got an immersion wort chiller by your side, dunk that bad boy directly in the mash and turn on the water to quickly chill the wort.

Just be careful not to over cool the mash. Stir with the chiller and check the temperature very frequently.

Can you think of some other ways to get your mash temps back on target?
Todd is a man of many hobbies. Obstacle course racing, programming, cooking, snowboarding, thinking of random business ideas, weight-lifting, beards, and most recently homebrewing. With little time to become a full-fledged beer geek, Todd focuses on the practical side of brewing. He’s always looking for ways to improve his process and shorten the brew day without sacrificing quality or control. Todd is an up-and-comer in the exploding Richmond, VA craft beer scene.