Mash temp too high - what effects?

Set my mash temp in software at 68 deg C (154F). Strike water came from the software at 75C (167F). I preheated the mash tun (a cooler) for 15 mins with boiling water, dumped it then proceeded to mash.

The strike water was a bit high at 80C (176F), but thought it would drop down during the 40min mash.

Checked a couple of times and at the end of the mash and the temp was a constant 76C (168F) inbstead of the ideal 68C (154F).

What effect will this have on the final beer? Brew was 100% pilsener grain.

Thanks in advance for any input!

You'll have fewer fermentable sugars. As the saying goes: M.A.L.T. (More Alcohol, Lower Temperature). And, the opposite is true. You might be able to throw something in to get those numbers up and get a little more dryness out of your beer, but I don't have the expertise to tell you what would work best. Sounds like you at least have a really nice mouthy session beer.

You mashed at 168 F. You probably killed the enzymes and didn't get much conversion.

Calder said:

You mashed at 168 F. You probably killed the enzymes and didn't get much conversion.

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that would be my thoughts. what was the OG of the wort? what was it supposed to be?

Calder said:

You mashed at 168 F. You probably killed the enzymes and didn't get much conversion.

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5 degrees is a huge difference, but ten? Step your game up.

Check the wiki https://www.homebrewtalk.com/wiki/index.php/The_Theory_of_Mashing


If a single temperature rest for starch conversion is chosen, it needs to allow for sufficient beta and alpha amylase actitiy. This is given at temperatures between 140ºF (60ºC) and 160ºF (70ºC), but only temperatures between 148ºF (65ºC) and 158ºF (69ºC) are commonly used. The higher the temperature the lower the limit of attenuation (fermentability) of the resulting wort will be. The following is a table that lists the relation between temperature and fermentability [Narziss, 2005]:

Temperature 140ºF (60ºC) 149ºF (65ºC) 160ºF (70ºC) 167ºF (75ºC)
apparent limit of attenuation 87.5% 86.5 % 76.8% 54.0 %

Brewing is a learning process. Make sure to remember the results of when you mash that high. But for next time, pour your strike water into your MLT first and keep taking measurements until the temp is where it should be. Too high? Leave the lid open a few minutes and stir. Too low? Take a little out and heat it, then add it back. Then add your grain. You'll hit your numbers pretty much every time.

Thanks for the feedback guys. I based the brew on approx 60% efficiency with an OG og 1.048. Just checked the gravity and ready right on 1.048. I'm beginning to wonder of I misread the thermometer (dial gauge) - time to invest in a digital.

ShakerD - good table there - will be interesting when I measure FG's to see how the attenuation works out.

Bmorebrew - great advice on the temp control in the mash tun (cooler). I have not been doing this and relying on temp reading for strike water straight from the stove.

Final thought - don't rush things! Wife was on my back to head out to a function that we needed to be on time for. Classic reason for making mistakes

My experience is that unless you really stir your mash, temperatures will vary quite a bit within the mash. Also, thermometers can be inaccurate over part of their range.

Since you hit your OG, you didn't denature all the enzymes but you may have a bunch of unfermentable sugars in there. Ferment it out and see how it tastes. Get a cheap digital thermometer and when you mash next time use both thermometers and see how they compare. Stir the heck out of your mash before you close the lid of the mash tun.

Bring some water up to a boil and see how accurate you're gauge is (assuming it goes that high). If its accurate at 212 is should be pretty close at 170.

A good rule of thumb for a mash is strike water is 12 degrees higher than desired mash temp. not perfect but will be pretty close and not kill all enzymatic reaction, which is most likely what happened, 176 -> 164 (you got 168) so for 154 about 166-8? you really don't want to use strike water over 168 ever, because it will shut down enzymatic reaction and once stopped it does not start again.

I (and a lot of other people) don't preheat the mash tun and throw the preheating water away.
Instead, we heat the strike water to about 6 deg C ( 10 deg F) hotter than it needs to be, add it to the tun, and wait while it warms the tun and cools to the required strike temperature. When it has cooled to the desired strike temperature (which takes about 10 - 15 minutes), we add the grains, stir, and mash as usual.
You may want to try this on your next brew.

-a.

You would have probably been fine if you didn't dump the preheat water.

I used to heat my water to about 175. I added for heat loss to the cooler and then the grain. Ended up at 153 almost every time.

Now I brew electric and use a pid. Best investment ever

I thought I had this problem just now - my recipe said to mash at 150. It seemed pretty close when I mashed in, and I left a candy thermometer in the tun for 90 mins and didn't open it. At the end, the thermometer said 160 at the top of the mash, but the first quart of runnings were 148. Is that bad?

Heat rises?

I just did the same thing using the POS thermometer that came with my turkey fryer. After my smoked ale has been in primary for 2 weeks I am still at 1.030 (OG was 1.041 as recipe predicted). Just did a check of the thermo and found that at boiling it reads 195 degrees. Damn! I think I may just bottle it anyways and see what happens. What do you guys think?

Sounds more like a fermentation problem than a mash temperature problem.

Mashing at the low end of the saccharification range should yield a drier wort, i.e. more fermentable sugars.

OG2620 said:

Mashing at the low end of the saccharification range should yield a drier wort, i.e. more fermentable sugars.

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If his termometer is reading 17* low, then what he thought was 155 (guesstimation on what temp one might use), he was actually mashing at 172*, which would likely result in very few fermentable sugars, and a high FG.

What should you do? Bottle / keg it, and drink it. Study the way it tastes, and move forward to the next batch.

BadNewsBrewery said:

If his termometer is reading 17* low, then what he thought was 155 (guesstimation on what temp one might use), he was actually mashing at 172*, which would likely result in very few fermentable sugars, and a high FG.

What should you do? Bottle / keg it, and drink it. Study the way it tastes, and move forward to the next batch.

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Math before coffee = fail.

You are correct! On both counts!