Overnight mash question

WelshPaul · Apr 14, 2013

My place is pretty cold right now due to the weather and I don't have an airing cupboard or similar to keep the mashtun in.
If I do an overnight mash (or more likely, start the mash in the morning and do the boil after work), what are the consequences of the mash temperature dropping too low?

pearse_uk · Apr 21, 2013

Consensus has it that an overnight mash might end up producing a dry beer. I'm sure someone else will provide the science! I've overnight mashed a few times and noticed no real difference - but have followed the advice of starting the mash at a little higher temperature to compensate - works for me!

PD · Apr 21, 2013

wrap up well and try and keep mash temp for the first 2 hours, then it dont really matter if it drops 10-12 degrees

zgoda · Apr 22, 2013

This weekend I did 1st overnight mash. Wrapped my mt in 2 blankets, yet still lost 20c in 10 hrs. I hope it will not end up being too dry, as it was only 1.038 bitter. Anyway, I mashed at 67c for 90 mins, then raised temperature to 77c with hot water and left for night. I guess the long mash in temperature over 70c deactivated most (if not all) beta-amylase, but that's only my speculation. I'll report back the result in 10 days. :)

graysalchemy · Apr 22, 2013

pearse_uk said:
Consensus has it that an overnight mash might end up producing a dry beer. I'm sure someone else will provide the science! I've overnight mashed a few times and noticed no real difference - but have followed the advice of starting the mash at a little higher temperature to compensate - works for me!

I don't get dry beer and mine has dropped to 53c at mashout and my mashes are typically left for 16hrs in a a workshop which reached 0c in winter.

What you need to do is make sure it is well insulated far beyond what you would normally do so plenty of blankets sleeping bags bubble wrap. However the most important thing to do is fill the void between the mash and the top of the tun. Add a later of silver foil on the mash then fill a bin bag with bubble wrap then put this in the tun.

The reason why an overnight mash works and why you can lose temp is because saccharification usually only takes 2 hrs or so so as long as temp is held during this period then you are fine further lowering of temp after saccharification isn't going to thin the beer as saccharification has finished there is no more starch to convert. The one thing however I have read is that if the temp drops below 50 then it is possible that bacteria and wild yeast could spoil the wort. But why does that matter if I am going to boil I hear you say? Well they could cause off flavours which will stay with the beer. However I haven't come across this in any of my beers and it was an american site that I read that on.

What you will get is better mash efficiencies probably into the 80's. I would do a few brews and then work out you mash efficiency before adjusting you grain bill.

Have Fun. :thumb: