Very low mash temperature

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BOBTHEukBREWER

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I left my digital probe thermometer switched on on a kitchen worksurface and noticed it read 27 deg C. Kitchen is cooler than that so I compared it to an outside thermometer. Conclusion - it is reading 10 deg C high. I mashed at 69 deg C so in reality 59 deg C. I used 6 lb pale malt with a final volume of 3.5 uk gals having OG 9 Brix. Yeast pitched was Nottingham. Any guesses how the beer will turn out, I will give feedback in 4 weeks or so. I have ordered a new one with a shorter probe. I intend to calibrate against that each brew day but use the old thermometer, providing it is consistent error.
 
At 59C you are still on the very low end of main conversion so I think you should at least get a consumable product although a bit thin.
 
I was thinking about this a bit more. At the end of the mash I raised the temperature to 80 deg C I thought - which was really 70 deg C. So the mash had another 20 minutes with the temperature climbing to a true 70 deg C. There is a nice white rocky ahead in the FV, and when I scraped it off I moticed the wort was exceptionally clear. It smells good too it was a SMASH brew with MO pale malt and Simcoe hops.
 
More than likely you got full conversion, but had more beta-amalyse and limit-dextrines reactions, making for a more fermentable wort that will have less residual sweetness and body in the finished beer. This may lead to a lower FG than you had planned. As an example, I had a Belgian Golden (yes, that one...) that I intended to mash at 60 C for 20min and 70 C for 40min. I missed low on the initial mash temp and the ramp up was slower than it should have been (caught it too late). The beer had an OG of 1.071 and a FG of 1.010. 85% attenuation when I was expecting 77%!
 
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