MT temperature drop

[Jerry Cornelius]

Just tested my MT, 33L bin with a plate for a false bottom. Wrapped in one layer of camping mat (6 mm) and covered with a blanket.

I filled it with 15 L of water at 79 C. An hour and a half later it was 62 C.

How much difference will the grain make? Do I need more insulation?

On a positive note, the boiler and IC work fine.

[Robdog]

I think the grain will make a big difference and you wont see so much of a drop. I would have though grain would hold heat well.

[WishboneBrewery]

2 layers of camping mat would be better and don't forget the lid and base.
here's mine done with camping mats viewtopic.php?f=6&t=24552#p272007

[Jerry Cornelius]

Thanks chaps.

Tomorrow's the big day. Just need to settle on a recipe. Something simple like Caroline's, I think.

[Dr. Dextrin]

I've just built a new MT from a cool box and did a similar experiment. With water in the tun it dropped rather too much (about 3 degrees) over an hour. Not surprising really considering the cool box insulation - if you take it apart and look inside - is pretty pathetic. I'd read on this forum that with grain inside the temperature drop would be a lot less but that didn't make sense to me. Let me explain...

The thing with water is that it convects as it cools. That mixes it up, so the whole lot loses about the same amount of temperature throughout. With a real mash inside, however, it doesn't convect. So the middle of the mash stays hot. If you measure in the middle, you'll be fooled into thinking it's retained the heat better, but it hasn't really because it's just cooled a lot more at the edges. Basically, the tun will lose much the same amount of heat no matter what's inside it - that's just basic physics.

On my last brew, I found the temperature in the middle of the mash remained pretty constant, but when I measured at the edges it had cooled by up to 5 degrees. The cooling extended into the MT by a centimetre or two (more in the corners). When I stirred the whole lot and measured again in the middle, the drop was 3 degrees - about the same as I got when using water alone.

So basically, if your MT isn't well insulated and doesn't pass the test with water in it, you could be mashing the outer part of your grain at significantly lower temperatures than you want. I can't see that being good for beer quality, so that's why I've now built an insulated box to put my MT in. I've yet to see what difference this makes, but I reckon 50mm of expanded polystyrene should improve things a lot. Doubtless camping mats work just as well and are obviously better suited to circular tuns. However, I'd test again with water to be sure you've got enough insulation on there.

Of course, whether this matters to you depends on how fussed you are. I just wanted to point out that grain doesn't really hold heat any better than water. It just looks like it does.

[Parva]

I don't have any issues with my coolbox mash tun. Temperature drops by at most 1.5c over the course of 90 minutes and that's measured both at the edges, corners and middle. The grist does make a huge difference to the ability of the mash to retain heat, regardless of what the previous poster says.

[WishboneBrewery]

Given the numerous posts there have been reporting concerns over significant temperature losses while conducting trial runs with water alone I seriously doubt your own figures of 3 deg, 10-15 deg c or more is much more common without grain, I get more than 3 deg c in my well insullated mash tun and the water is heated in the mash tun itself.

Without any Preheating with and just using water, my mini mash tun only lost 3.5 Deg C over 2 hours - (2 layers of camping mat all round and 3 layers on the lid with a side skirt)
Time :: Temp
19.36 - 61.1 C
20.38 - 58.6 C
21.06 - 58.0 C
21.35 - 57.6 C

When the Tun was used with Grain in (pre-heated with hot Tap water) it the temperature drop over approx 105 minutes was 2.1 deg C, the temperature was taken from the centre of the mash with a probe on a wire and the tun was never opened during the steep.
I'm pretty happy with that

I prefer to heat the water to ~8 deg c above strike heat and allowing the temperature to stablise at strike heat before mashing in while I get on with something else.

I think that is a blooming good idea, my process of transfer using a jug obviously lost me quite a few degrees once the liquor was in the tun leaving me to top up with boiling water to reach the right strike heat. I'll be giving this a go on Saturday for my next brew, whether or not I'll pre-heat the tun with tap water I'm not sure

[trucker5774]

My most recent mash lost less than 1C......I'm sure the warm weather has helped. It is a £7.00 Asda cool box which I stripped and filled with expanding builders foam. It was a 5KG mash and the tun capacity is 24 litres

[trucker5774]

Youre right Chris............it's a warm box!

[Garth]

Like Chris does, I also drop my mash water into my tun at about 80C and leave it for 10 mins, this heats the tun up itself, then when it's at 72C I drop the grains in, this generally steadies itself at around 65/66C, using a coolbox my mash used to drop 1 - 1.5 degrees over 90 mins, now using a Nordic thermobox it drops less than a degree, it's all about the preheating that stops the drop later on

...and agreed, mashed grain holds better temperature than just water alone.

[WishboneBrewery]

[Dr. Dextrin]

I'd just suggest you peeps should try sticking a thermometer down the edge of your tun at the end of mashing and see what the temperature is. If it's not the same as in the middle (and assuming you pre-heated), you might benefit from more insulation.