Weird happenings with mash temp

[Clanchief]

So I was brewing an american wheat yesterday. I plugged my recipe into Beersmith as I'm wont to do, and it spit back out some numbers in terms of temp and volume of water for my mash. Around 3 gallons for my grain bill on the mash, at 160, to get an actual mashing temp of 148. So that's what I did. I put the water in the tun to heat it up a bit before I added my grain (about 15 minutes) then put my grain in. However, I ended up way low on my mash in - 142. 6 degrees short of what I thought I'd get. I added a quarter gallon of boiling water and that put me right at 148, so I was OK. Here's the question: what would cause that dramatic difference in temperature? The conditions were mild - 75 degrees outside, light wind, not on the mash tun. My grain bill was:
4# pilsner
3# white wheat
1# crystal 40
5 oz. Carapils
4 oz. Special B
8 oz. rice hulls

I crushed the grains to .037. I ended up with a good efficiency (75% or so) so I'm not complaining about that, but this is the first time I've ever had my temperature end up so dramatically far off what I was shooting for.

 

[acidrain]

Do you have you equipment profile set correctly in BS?
Do you always let the HL set in the MT for 15 minutes or so? Was the lid on?

 

[Clanchief]

Do you have you equipment profile set correctly in BS?
Do you always let the HL set in the MT for 15 minutes or so? Was the lid on?

Yes, yes, and yes. I have done the same thing every time I've done an AG brew. Well, that's not entirely true. I have sometimes heated the mash tun with separate water, not my mash water. I think the only real difference was the rice hulls, which I haven't used before. Other than that everything was the same. Equipment profile was set correctly, the lid was on, I pre-heated the mash tun.

 

[Yooper]

If you're using a cooler, did you preheat the cooler first? If not, the cooler will "suck" out the heat and the temperature will drop very quickly. If you preheat the cooler by adding 180 degree water, and then let it drop to the strike temperature, the cooler will hold heat perfectly, losing less than 1 degree in an hour.

If you're not using a cooler, what do you have for an MLT?

 

[Clanchief]

If you're using a cooler, did you preheat the cooler first? If not, the cooler will "suck" out the heat and the temperature will drop very quickly. If you preheat the cooler by adding 180 degree water, and then let it drop to the strike temperature, the cooler will hold heat perfectly, losing less than 1 degree in an hour.

If you're not using a cooler, what do you have for an MLT?

I was using a cooler, and to pre-heat it, I added the mash water in advance. I've done this before without losing this much heat. Previously it had only been around 1 degree in temp loss. But I'll look at adding a higher temp water first to heat the MLT.

 

[Yooper]

I was using a cooler, and to pre-heat it, I added the mash water in advance. I've done this before without losing this much heat. Previously it had only been around 1 degree in temp loss. But I'll look at adding a higher temp water first to heat the MLT.

Yes, either add the water at 180 degrees (higher will crack/warp your cooler- as I know from experience), or do a separate addition and let it sit for 15 minutes and drain, and then add your strike water.

 

[Natdavis777]

Yes, either add the water at 180 degrees (higher will crack/warp your cooler- as I know from experience), or do a separate addition and let it sit for 15 minutes and drain, and then add your strike water.

+1

Thats what I did with my cooler and always maintained a steady mash temp. I too learned the hard way when I didnt pre heat with water that was warmer than strike temp and doughed in.