first multi-step mash, overshot my target temp

I usually just do single infusions, but over the weekend was in the mood for a summer beer so I brewed a Belgian Wit. With the wheat in the grain bill figured I should try my hand at a beta/protein rest for the first time. I used Palmer's formula which I'll paste below, and long story short when I infused to raise the temp from 120 up to sacc rest, I came in quite a bit high (like 170!).

So if you see anything I missed below, or if maybe this formula is outdated, please let me know.

I'm guessing part of the issue can be attributed to a hot spot when taking the temp, but 5 mins after the infusion and not seeing much of a change, I didn't want to chance it any further so added 2 cups cold water and 2 ice cube trays and stirred, and within about 10 mins it was in the 152 range.

I imagine I denatured the beta, but just going by the heavy airlock activity in these first 48hrs it seems at least there were sufficient fermentables. So, looking at the formula I used, I found that for whatever reason I added about 2G of boiling water instead of around 1.5G needed to raise the temp.

Aside from that, I'm questioning whether I should've accounted for some grain absorption (for the initial 2.5G I infused with for the first rest)? Also, I noticed a bit of warping in the cooler -- is it generally accepted to use boiling water for stepping up the mash temp? Or should I adjust the calculation for something like 190deg infusion water?

As always, I appreciate any feedback so I can try and learn from what I did wrong

Mash Infusion Equation
Amount boiling water added (in Qts) Wa = (T2 - T1)(0.2G + Wm)/(Tw - T2)
where:
[[my values -- (152 - 120) (0.2(10) + 10)/(210 - 152) ]]
*came to 6.6 qts of boiling water to raise the temp from 120 to 152

R water/grain ratio (Qts/lb)
Wm total amount mash water (quarts)
T1 initial mash temp
T2 target mash temp
Tw actual temp of infusion water
G amount of grain in mash

The formula and math seem fine. I put 10# grain, 10 qt water, 120F->152F into ProMash and it also predicts 6.6 qt of 210F water. I've done this for step mashes and always use more water than predicted... The key is to calculate the water and boil double that. Just add enough boiling water to get to 152F and combine the extra water into your sparge to save the heat. ProMash predicted 130F mash-on temperature to get 120F mash temp, not accounting for heating the cooler.

DSmith said:

The formula and math seem fine. I put 10# grain, 10 qt water, 120F->152F into ProMash and it also predicts 6.6 qt of 210F water. I've done this for step mashes and always use more water than predicted... The key is to calculate the water and boil double that. Just add enough boiling water to get to 152F and combine the extra water into your sparge to save the heat. ProMash predicted 130F mash-on temperature to get 120F mash temp, not accounting for heating the cooler.

Click to expand...

Yep, first infusion was 130 which settled right at 120F. Since you mentioned it, I did preheat the cooler a little longer than usual just because I got sidetracked with something, probably 20mins or so with 170deg water. Not sure what impact that would have if any, but it's worth mentioning I suppose. Thanks for the response

As long as you cooled the preheated water to 130F, you're ok. It would take a long time without a lid on to cool 170F water to 130F for preheating the cooler. 10F is enough extra temperature to preheat a cooler. But if you measured 120F mash temperature the preheating is probably not the problem.

I don't think you could ever get to an even mash temperature of 170F by infusion from 120F. That would take a lot more than 2 gallons of boiling water. Using more boiling water than calculated seems normal. I question the thermometer.

Yeah, in hindsight I probably could've stirred it around better and taken a couple more readings in different spots. Or at least, that's what I'll chalk it up to if it ends up fermenting down to the expected FG