Maintaining mash temp in oven - what temp?

If you have experience using an oven to maintain your mash temp (at the typical 150F) what oven temp do you find works best for you?

I did a partial last weekend and made a Celcius/Farnheit units error and set my oven at 150C instead of 150F, but far from being a disaster it actually maintained my mash temp right around where I wanted it instead of adding heat as you might expect!

In another thread SilverZero commented:

SilverZero said:

A 250F oven won't add much temp to that much water if any at all, but 150F air will take heat from the pot.

Click to expand...

So for future reference I'm curious to know what sort of temp range I should be keeping my oven to.

I use 170 and was concerned at first it would keep bumping up my mash temps. As you found at a higher temp, it's a lot of thermal mass.

EDIT: By the way that's just because it's as low as my oven goes.

It's all going to depend on what temp you want to maintain and how big your mash volume is. I typically will only steep or do part mashes in the oven, so I'll typically set at about 160F figuring I'll lose a couple of degrees over time. I usually check the temp periodically just to make sure it hasn't dropped too much. Butsince I'm not doing a full mash I don't worry about the exact temp as long as it stays between 150F & 160F.

I have my mash stockpot virtually full to the brim. I heat the oven to about 250°F then turn it off. By the time I stir the mash and put it in the oven I find the temperature holds perfectly for an hour and there is no need to turn on the oven. I stir it about 3 times in the hour while in the oven. I have a cheap digital thermometer which sits on top of the oven with the sensor lead in the mash pot.

I've done this twice before upgrading my pot size to something that wouldn't fit in my oven. My oven only goes down to 170f so I left it at that, and occasionally checked popped the door open a tad to let some heat escape, seemed to work fine.

Probably fine to leave it at 170 for the first 30mins of your mash and kill the heat after, should hold it fine.

Ideally you'd set the oven to the exact mash temp you want but most only go down to 170F on the dial. You may find that the controller is pretty far off though so it's best to put a thermometer in there to know for sure.

Bobby_M said:

Ideally you'd set the oven to the exact mash temp you want but most only go down to 170F on the dial. You may find that the controller is pretty far off though so it's best to put a thermometer in there to know for sure.

Click to expand...

I suspect that is not the case going by my own 'mistake' and what SilverZero said - '150F air will take heat from the pot'. I think the ideal oven temp will be significantly higher than the mash temp you want to maintain due to the physics of heat capacity of air verses liquid.

i don't know. that doesn't sound right. from everything i've read heat transfer only happens between things with different temperatures.

The lowest setting of my oven is about 155-160, that I checked with an oven thermometer. I do partial mashes and turn the oven on until it heats up. Put my pot in and leave it on for the first 10-15 minutes, turnit off and I maintain my temp with a degree or two.

When you preheat your oven, the thermostat turn off the element when the thermostat reaches the set temperature (or close to it if the thermostat is accurate, most aren't very accurate). The rest of the oven may not be that warm. The rack you set your kettle on may be quite a bit cooler so you can lose heat from the kettle through conduction. Also, the walls of the oven won't be up to temperature either so your kettle can continue to lose heat due to radiation. If you were to heat the oven for an hour prior to putting the kettle in there all part of the oven would be nearly the same temperature as the thermostat and your heat loss from the kettle would be zero, assuming that the thermostat was accurate.

Have any of you tried to just put a towel or two over your pot? I have found that I can do that and maintain temperature for an hour.

warex said:

Have any of you tried to just put a towel or two over your pot? I have found that I can do that and maintain temperature for an hour.

Click to expand...

I would tend to go this direction if I didn't have a converted cooler. A few towels and you get enough insulation to hold the temperature steady enough for an hour.

You've already got a large mass that is going to take a very long time to cool naturally in room temperature if it has an open lid.

aidan said:

I suspect that is not the case going by my own 'mistake' and what SilverZero said - '150F air will take heat from the pot'. I think the ideal oven temp will be significantly higher than the mash temp you want to maintain due to the physics of heat capacity of air verses liquid.

Click to expand...

I'm not well versed in physics ore thermodynamics, but this would definitely be one of those phenomenas that go against common sense if it is true.

What this suggests is that if you took a 2 ton block of steel and heated it through and through to 150F and then put it into an ambient environment of 150F, the air temp would rise ABOVE 150F because the steel block is "full" of heat to give off? I don't buy it. Temperatures of various objects/gases/liquids in proximity tend to seek equilibrium and THAT's where each object's heat capacity matters. In other words, in the above example, if the ambient temp in the room was 50F and the 2 ton block of steel is 150F, the equilibrium will achieved will be closer to 149F.

PERHAPS a 150F oven will waver between 155 and 145 due to heat losses to the room and the thermostat's offset. In that case, sure running it ~5F hot will help. Truth is, most mash tun heat loss is due to an ambient delta of over 80F. +/-10 is not the end of the world.

aidan said:

I suspect that is not the case going by my own 'mistake' and what SilverZero said - '150F air will take heat from the pot'. I think the ideal oven temp will be significantly higher than the mash temp you want to maintain due to the physics of heat capacity of air verses liquid.

Click to expand...

I'm not well versed in physics ore thermodynamics, but this would definitely be one of those phenomenas that go against common sense if it is true.

What this suggests is that if you took a 2 ton block of steel and heated it through and through to 150F and then put it into an ambient environment of 150F, the air temp would rise ABOVE 150F because the steel block is "full" of heat to give off? I don't buy it. Temperatures of various objects/gases/liquids in proximity tend to seek equilibrium.

PERHAPS a 150F oven will waver between 155 and 145 due to heat losses to the room and the thermostat's offset. In that case, sure running it ~5F hot will help. Truth is, most mash tun heat loss is due to an ambient delta of over 80F. +/-10 is not the end of the world.

So, bottom line, what temp should the oven be set to? As close to your mash temp as you can get it but anything is better than room temp if you don't have insulation.

rycov said:

i don't know. that doesn't sound right. from everything i've read heat transfer only happens between things with different temperatures.

Click to expand...

This... Though to clarify:

Temperature is a measure of the kinetic energy in a given substance. It's the energy differential that means something, here. The air in the oven will not "leech" energy from the pot, though the water will evaporate and add energy to the air.

Either way, if you left a cool pot in a 150 degree oven, eventually your pot will reach and maintain temp at 150. It won't go over, and something over 150 will eventually cool to 150.

i set my oven to the lowest setting then turn it off when the thermo inside hits 150°

i mashed at 158° this weekend, placed in oven (off) at 150° and turned it on brielfy about 2/3 of the way through to keep the oven around 150°

after a 60+min mash my temp was still 157-158°

I wouldn't rely on the temp on your dial, I always use the internal thermometer

Bobby_M said:

I'm not well versed in physics ore thermodynamics, but this would definitely be one of those phenomenas that go against common sense if it is true.

Click to expand...

I was thinking the same thing initially which is why I was curious to get to the truth of the matter. I found it really surprising that keeping my mash in a 300F oven for 1 hour didn't add any significant heat to it. Based on this and what other people report, it seems you can have quite a large range of oven temps and still maintain pretty consistent temp of your mash. Next time I'm using oven to maintain mash temp I'll try closer to 150F.

warex said:

Have any of you tried to just put a towel or two over your pot? I have found that I can do that and maintain temperature for an hour.

Click to expand...

might try that next time

aidan said:

I was thinking the same thing initially which is why I was curious to get to the truth of the matter. I found it really surprising that keeping my mash in a 300F oven for 1 hour didn't add any significant heat to it. Based on this and what other people report, it seems you can have quite a large range of oven temps and still maintain pretty consistent temp of your mash. Next time I'm using oven to maintain mash temp I'll try closer to 150F.

Click to expand...

I guess it's not that crazy. Look at the thermal mass of a 20 pound turkey and how frickin long it takes to get it up to 165F internal temp. Mashing 4 gallons of water and 15lbs of grain or whatever it is has at least twice the heat capacity.

warex said:

Have any of you tried to just put a towel or two over your pot? I have found that I can do that and maintain temperature for an hour.

Click to expand...

Ya, I mash in my SS kettle, and I just wrap a towel around it. I lose about 1 degree in an hour mash.