MLT size

Hi all.
I am using a 52 quart cooler I converted to a MLT... I am having some problems holding my temp.
Is there just too much head space to hold my temp? I have been pre-heating the cooler with hot water and insulating with blankets and kept the lid down the entire time but my last mash I went from 152 to 146 in the hour.
I missed my target by a mile and I am pretty sure this was a major factor.
Is there a recommended size to stay within?
Thanks
Jim

That depends on the shape of the base.  I switched to ah 48qt ice cube last week, and I dropped from 153 to 150 in 75 minutes.  Most of that was lost when I stirred.

But, if you've got one of the longer rectangular coolers, then that much exposed surface area may allow more evaporation and thus cooling.  Here are a couple of ideas:

1.  create a mash cap out of 1" foam insulation covered in foil and foil tape.  Cut it about 1/2" smaller than the inside dimensions of your cooler. 

2.  Heat your strike water to about 10 degF above your target.  Pour your strike water into the cooler and close the lid. Shake the water around the cooler for a few minutes.  Then open and check the water temp.  Either stir the water, or shake the cooler some more until it reaches your strike temperature.  This will more thoroughly pre-heat your cooler.  It also makes sure that the water is exactly at strike temp when you begin to dough in.  You can even start to dough in while still several degrees high.  Then stir the mash until you hit the mash-in temp exactly.  Again, you are making sure that you are as preheated as possible and that you are not losing heat to stirring.

3.  You can add insulation to your cooler.  *I* was planning on making a larger box around my cooler, and filling it with great stuff foam.  An extra inch of insulation should be plenty.  I was going to make my shell out of that mylar coated bubble wrap insulation, and aluminum tape.  Then fill with foam and wait for it to harden.  Maybe $20.

4.  You could buy an Ice Cube cooler.  I have the 48 qt one without wheels, I like it because it has a perfectly flat bottom.  The one with wheels has a funky shape to it.  There are several threads over on homebrewtalk.com that discusses how to convert the wheeled ice cube into an MLT. 

I use a 48qt rectangle Coleman cooler, have had no problems holding my mash temp. Although the lid is not insulated, I just throw a blanket on top of it.

I was thinking about making an insulated box for the cooler. I have some stuff laying around and will give that a try.
I also like your idea about heating the tun with the strike water. I have been adding hot water and tossing it... Probably just not hot enough.
I will try one more brew with this cooler. If it goes south I will take my conversion and move it over to a smaller cooler and see where that goes.
Thanks!
Jim

The specific heat of the cooler material is actually pretty high...three times that of metal.  Plus, being an insulator it conducts the heat very slowly.  So, it can take a while for the heat to equalize throughout the material of the cooler. 

If you were just using hot tap water to pre-heat the MLT, I think you'll be fine using the strike water approach.  There are a lot of threads over on homebrewtalk about this same problem with the larger ice cube coolers.  They were loosing 10 degF until they switched to the strike water approach.  Afterwards, they were down to 1-2 degF which had more to do with opening the lid to check the temp.

Just don't go over 180 degrees...it will warp the cooler.

I lay a round piece of pink foam board right on the grains in the MLT to keep the heat in the grains, and isolate the dead air from there up to the lid. 

And punched a hole for my digital thermo, which I put in hole at finish to get temp while I'm preparing the vorlauf/recycle. 

MaltLicker said:

I lay a round piece of pink foam board right on the grains in the MLT to keep the heat in the grains, and isolate the dead air from there up to the lid. 

And punched a hole for my digital thermo, which I put in hole at finish to get temp while I'm preparing the vorlauf/recycle.

Click to expand...

Does the foam absorb water? Sounds like a good idea but I would be worried about if the material leached anything off.

No, it's that dense pink foam and has a slick surface on the flat sides.  Like the attached.  I also use it for the "top" of my lauter arm for sparging. 

Imagine a smaller circle just laying on the mash, with about a quarter-inch of space around the perimeter. 

The lid of my Ice Cube 60 qt. cooler was hollow and during the first use I noticed that the lid became warmer than the rest of the cooler during the mash.  I lost about 5 degrees during the mash period.  I drilled a few small holes in the lid and filled the lid with foam crack/insulation.  The foam expanded to fill all of the air space.  Now, I might lose 2 degrees (max) during a prolonged mash.

Thanks to all for responding.
Here is what I came up with and possibly a chance to improve my brewing system.
I went to the home store and bought an 8 foot sheet of foam insulation with a reflective backing on one side. I built a box with a floor that fit the cooler with enough room to wrap the cooler in blankets. I had some foil tape laying around so the cost was around $16 for the insulation. I also had a a lot of help from my wife. She helped me with the build and spent the afternoon with me while I brewed an American Wheat.
We both realized that even though Beer Smith calculated the strike water temp at 168 deg and we followed Tom_Hampton's advice of adding the strike water 10 deg higher and letting the cooler absorb the heat. I left the cooler under the blankets and cover for a while and added my grain bill. I was having trouble hitting my temp. I ended up having to use some of my sparge water heated up to the mash to get the temp. I finally hit my temp and insulated my cooler for the hour. After my hour my temp loss was about 2 degrees. I wasn't too confident and left out a gallon of sparge water. I was 2 points higher than my target and happy at that.
With all that my wife commented that it was an awful lot of trouble to get and hold my temp. She asked why I couldn't use my old turkey fryer on the burner and adjust my heat accordingly. I looked at my pot and now realize that she might be right. I have posted some pics of the insulator box and the pot with the current spigot on and off. I am looking at how I can get a braid on the current spigot or how I might be able to add a weldless spigot and bazooka on the pot.

Twangthang said:

Beer Smith calculated the strike water temp at 168 deg and we followed Tom_Hampton's advice of adding the strike water 10 deg higher and letting the cooler absorb the heat. I left the cooler under the blankets and cover for a while and added my grain bill. I was having trouble hitting my temp.

Click to expand...

+1 to adding too-hot water first, and then when it hits the strike temp, adding grains.  This is much more consistent than adding water to grains. 

Inside the mash profile, there are numerous data points for the MLT temp, grain temp, and a check box to account for preheating and the deadspace.  You may wish to review those as each affects the calculated water temp you're adding.  For ex, I think the default grain temp/MLT temp is 72F.  If your stuff is really 60F in the garage, then the strike will be off. 

You don't have to put the "_" in my name .  I'm really just Tom (or Tom Hampton if you insist on using my full name).  8)

If you think that was a lot of trouble, direct firing a pot on a burner with 40 lbs of barley porridge will NOT be more fun.  Think hot spots, constant stirring, burned grains, etc.  There are people who do it, but they work pretty hard and making a setup that will work for it.  A LOT harder than making a foam box cover for a cooler.  There are also recirculating systems RIMS and HERMS that are "easier", but again require building and purchasing a pump, temp controller, etc. 

As Mr. Licker  suggested, something isn't right in your mash profile if your mash temp still came out low.  Probably grain temp, if I had to guess...because you have equalized everything else (MLT and Water). 

There will always be times that you end up low for some reason.  You can infuse as you did or decoct.  I usually decoct because I prefer not to mess with my mash thickness.  If you infuse, its easier to do with boiling water than water at sparge temp (you will need less anyway).  Beersmith will tell you how much to add to adjust with the mash-adjust tool. 

Another thing you can do, is dough-in while the strike water is a few degrees high.  Then you stir the mash until it falls to exactly your desired mash temp.

How far off was your dough-in temp ?

Sorry about the " " Tom...  ;D
I think my dough in temp is my problem. I appreciate your insight on the burning, stirring etc problems I am sure I really didn't consider.
I think the box and blankets has taken care of my temp loss during mash.
My dough in temps is really where I am having my problem.
I am pretty sure I haven't given all the info to BeerSmith it needs. When I doughed in I was having trouble with my temps there. I wasn't too sure if pouring boiling water would be a bad thing so my first batch of sparge water was hot (180 deg) but didn't raise my mash temp high enough so I made a second smaller infusion of boiling water and _finally_ hit my temp.
I have been reading around about watering down the mash and there seems to be some differing opinions about mash thickness... My mash was afterall about 2 quarts thinned...  Is this something to be avoided?

<---Jim