Affect of Hot mash going "cold" on sweetness

I tent to like my beers a bit sweeter, not dryer. I have only done 4 AG batches and start them out "hot" - 158 or so - but by the end of the mash it is almost 10 degrees cooler. (its a regular round igloo cooler so im not sure why it loses so much heat, but thats for another discussion...)

Does not being able to hold a hot mash mean that the beers will be dryer? I know if you start hot and keep it hot, it will be sweet, and if you start cool and end cool it will be dry. I couldnt find anything on what happens if you start hot and end cool.

Help me out pros!

You want to account for temperature loss, a higher mash temp 156-158 will give you more unfermantables giving it more body, mashing at 150 will give you a drier beer. Also attenuation off yeast plays a factor

Try preheating your mlt.

Runningonbrew, I know that the hotter mash temp will provide more unfermentable sugar. What I dont know is that if the temp drops a lot, will the unfermentable sugars that the hot mash created then become fermentable?

Rehlgood, I tried that. And I only open the cooler once to give it a stir. Still loses temp...

A higher portion of unfermentable dextrins does not necessarily mean "sweeter". You might try a combination of crystal malts and lower IBU's to bring out more sweetness.

It sounds like the mash isn't totally mixed when you're measuring the initial 158 temp. That's a huge drop for a cooler that you've preheated. I use a round igloo cooler too and I get maybe a one degree drop over an hour.

What kind of thermometer do you use? The ones with the probe can stay in the mash even with the lid on, so you can keep tabs on how it's settling.

I added a lot of extra insulation to my round cooler, AND insulated the bottom as well. Held temps a lot better. Also started setting the cooler onto towels, rather than my tile floors.

I had a mash go "cold" last September when we had the fires down here in Bastrop Texas. Was evacuated for several hours, and then had to set the mash aside for a day because we were packing things up expecting another evacuation. Batch sparged the next day, mash was below 120 F. Was a Belgian White, mashed in at 152. Came out WAY drier than before, I should have anticipated and reduced the sugar addition by half. Still came out amazing, the little bit of lactose souring was just right.

My guess is that unless you are holding your high temp for an extended period, you will still get a lot of Beta-Amylase activity resulting in a drier than expected beer. Perhaps count on adding Dextrose powder to your boil?

From what I have read, temperatures above 150 denature beta amylase rather quickly so you will get more unfermentables in your wort. The higher you mash in above that temp, the faster that beta amylase denatures. So if your mashing in at 158, and 60 mins later your below 150 it shouldn't matter, most of the starch conversion has been completed in the first 20 minutes and that beta amylase should be long gone since you already exceeded its denaturing temp.