AG Batch #1 - Mash Temperature Loss

[PittsburghBrewer]

I brewed my first all-grain batch yesterday. My target mash temperature was 151, but my mash was at 148 after 15 minutes, and 143 after 20 minutes. (At that point, I added 1 qt. of boiling water.) I'm trying to figure out why I lost so much heat.

Here are the details:

I used a 5 gallon Igloo Industrial cooler as the mash tun. I mashed 9.4 lbs of grain in 3 gallons of water. I added the strike water to the cooler at 175 to preheat the cooler, then stirred it until it reached 164 - my planned strike temperature.

By my calculations, that mash took up 3.75 gallons in the cooler. Could I have lost so much heat because I had 1.25 gallons of headspace in the cooler? Also, my instant read thermometer has a short probe (3-4 inches), so my temperature readings were made near the top of the mash. Could that have caused inaccurate readings? Finally, I realize now that I didn't put the lid on the cooler while preheating. Maybe the lid absorbed a lot of heat.

AG batch #1 was definitely a learning experience - lots of ups and downs. On the plus side, my mash efficiency was a lot higher than I expected!

Thanks for your help!

 

[brewshki]

I brewed my first all-grain batch yesterday. My target mash temperature was 151, but my mash was at 148 after 15 minutes, and 143 after 20 minutes. (At that point, I added 1 qt. of boiling water.) I'm trying to figure out why I lost so much heat.

Here are the details:

I used a 5 gallon Igloo Industrial cooler as the mash tun. I mashed 9.4 lbs of grain in 3 gallons of water. I added the strike water to the cooler at 175 to preheat the cooler, then stirred it until it reached 164 - my planned strike temperature.

By my calculations, that mash took up 3.75 gallons in the cooler. Could I have lost so much heat because I had 1.25 gallons of headspace in the cooler? Also, my instant read thermometer has a short probe (3-4 inches), so my temperature readings were made near the top of the mash. Could that have caused inaccurate readings? Finally, I realize now that I didn't put the lid on the cooler while preheating. Maybe the lid absorbed a lot of heat.

AG batch #1 was definitely a learning experience - lots of ups and downs. On the plus side, my mash efficiency was a lot higher than I expected!

Thanks for your help!

That does seem like a lot of heat loss. I would normally suggest to preheat the cooler, but it looks as though it would have been plenty warm if the water was in there and you had to stir to bring it down. Did you happen to take a temperature reading of your grain? Did you leave the lid on for the duration of the mash? Do you live in a particularly cold climate? Is your thermometer accurate?