MLT Temp issue / Low FG question

My last two batches have came out lower than the expected FG, and I think this is partly due to the temperature loss I have been seeing in my 10g Igloo MLT.

Here's my (latest) procedure;
Ambient 68* / grain 68*

• Heat 2g to 175 and put in MLT (wait 10 mins)
• Heat up the rest of water to 165~ish and add to MLT. (total temp around 165)
• Add my grains, (14# on last batch) stir and cover. (wait 5mins)
• Check temp, which was 153.
• Close lid, go about other brewing prep.
• Come back @ 60mins, temps 142. @$#%!!!

From what I've read, this should be a valid procedure. I'm thinking this might be due to the excess head space in the MLT. I'm looking for suggestions for two main things, what can I use/make that's food safe to fillup/lock down the heat in the head space, and procedure suggestions that may help on the problem. Thanks!

with that much temp loss i don't think it can be the headspace. with my 72 qt coleman, even with only 7 lbs of grain and an appropriate amount of water I don't lose that much heat. Check out if the lid is seating tightly and/or wrap the whole thing in a comforter or other insulation. Also stir right before takeing initial temp. you might be getting incorrect readings at first if you let it set for 5 minutes. I generally stir immediatly before takeing the temp.

Try not splitting up the strike water. Heat your entire strike water volume up to 172 or so, put it in the cooler and with the lid on, swirl it or tilt the cooler on all sides a bit so the water coats higher up on the walls. Perhaps I over estimate the effect, but once you add the extra water and grain, you're exposing the mixture to the cold non-preheated walls of the cooler up higher where the initial water added didn't touch. That could be good for 2F of loss but probably not what you're seeing.

I have to think you're leaking air through the lid and yes, restricting headspace air movement would help. You can cut a circle of rigid foam and then wrap it with some HDPE plastic sheeting. HDPE is food safe. Rest that on top of the mash and your'e good to go.

I use a Coleman 9gal cooler and after I dough in I wrap an old comforter around it. I don't think head space ia a problem.

Bobby_M said:

Try not splitting up the strike water. Heat your entire strike water volume up to 172 or so, put it in the cooler and with the lid on, swirl it or tilt the cooler on all sides a bit so the water coats higher up on the walls.

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When I added the second batch of water the total volume was around 170, so I let it sit with the top off for a little bit until it was at 165. It was around 4.5 Gallons, so less than half of the total space. I've toyed with the idea of filling it with the total amount of water and then move it back, but that's a PITA.

jetmac said:

I use a Coleman 9gal cooler and after I dough in I wrap an old comforter around it. I don't think head space ia a problem.

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I don't have any extra comforters around the house (none that the wife would allow me to live after using) , I do have a few beach towels. Worth a shot...

I went to the hardware store and got a few items for better testing, a hpde bucket lid that fits inside of the cooler to cover the top of the mash, as well as the parts for a diy thermowell. I think tonight Ill heat up some water and try them out with the addition of plasticwrap to seal the top of the cooler. What's the thought on testing this without grain, will it be that different? (less thermal-mass, so a faster drop?)

i get maybe 1-2° fall in my 10GAL Rubbermaid over 60 minutes.. I can't for the life of me think of why you'd be getting a 11° delta in yours... is it a round 10 Gal?

Tyrone said:

i get maybe 1-2° fall in my 10GAL Rubbermaid over 60 minutes.. I can't for the life of me think of why you'd be getting a 11° delta in yours... is it a round 10 Gal?

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It is, Rubbermaid branded with the Home Depot logo.

haha.. same one i have. No idea.. Weird..

Tyrone said:

haha.. same one i have. No idea.. Weird..

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Well that's good actually, that means its likely a procedure problem. I just installed the new thermowell and heating up some water. Let's see if its a derp problem or not.

Just finished a 6.5 Gal test on a heated tun. Started at 154.8 ended after 60min @ 151.2. It has to be procedure.
I do have another question, this last batch I was talking about was a AIPA (hopdevil clone), that started at 1.065, and ended at 1.009. Expected a 1.018. Could there be another situation (other than low mash temp) that can cause lower than expected FG?

You aren't using cold grain are you? Like, from a fridge?