Mash Tun heat loss & grist heat retention.

[AzimuthBru]

Hey guys, I have a quick question for you all. I am currently a mini-mash brewer and happened to have an extra picnic cooler that I converted into a mini-mash tun (sort of a practice run for when I can upgrade to all grain) After looking at how insulative the cooler was before & after adding the lautering device and ball valve I noticed that due to the conduction of heat to the outside through the valve with just H2O in the cooler I loose about 2ºF/10min. I am assuming that grain is more insulative than H20 and wondering if I will have such a steep loss of heat during an actual mash or if the avg. temp will be more stable with grain in there. Also, I will obviously have a temp. gradient in the mash due to the lautering device being on the bottom of the MLT, will this cause any issues other than maybe some loss in efficiency? What do you all think? Thanks for the input!

[maxwell]

A couple of thoughts:

1) Did you preheat the mash tun when you measured that temperature loss rate? In a cooler-type mash tun I see a loss rate of about 1-2 F per hour, so it could be that you're seeing a big initial drop as you're heating the cooler itself.

2) Grain has a lower specific heat capacity than water. I don't know about thermal conductivity though. PErhaps more relevant is that a grain+water mixture should transfer heat less efficiently by convection because water can flow only through the pore space between grains.

You should stir the mash periodically so that the grain sees an approximately uniform temperature when averaged over the duration of the mash.

[foomench]

What maxwell said. I preheat my cooler. After I mash in and get a stable temperature, it might drop a degree over an hour. Also, the lid on my cooler was hollow when I got it. I drilled two holes in it and filled with expanding insulating foam. Heat rises, and coolers are not designed to keep that in. That reminds me--I need to make an insulated lid for my keg HLT.

[AzimuthBru]

Thanks guys! Indeed I did pre-heat the tun. The reason the drop is so steep is because it's a small cooler, but insulating the lid is a great idea. I guess I'll just have to experiment. Which means I'll have to brew more... Bummer!

[Deathrider]

Also, the lid on my cooler was hollow when I got it. I drilled two holes in it and filled with expanding insulating foam. Heat rises, and coolers are not designed to keep that in. That reminds me--I need to make an insulated lid for my keg HLT.

Never really thought about the lid Now I have something else to do this weekend!

Thanks