Having trouble with temps in step mashing

Help! I'm getting very frustrated with not being able to hit the temps I want. I've done about 7 all-grain brews now and consistently end up about 10 degrees lower than what I'm shooting for when in saccharification temps. The past two or three mashes, I've done a beta-glucan rest(~110) and hit those temps just fine. I'm using brewer's friend step mash infusion calculator to figure out my volumes of boiling water. These past two times, I've gone ahead and put in enough water to reach the sacc temps, which ended up being 2/3 again as much as it calls for, giving me a super thin mash( ~3.5qt/lb). I've been preheating my mash tun ( a large Coleman Xtreme), and I just checked my thermometer (209 at boiling, 32.7 in ice water). I'm using a digital probe thermometer. When I checked the mash temp with an instant read and the temps were 3 degrees apart. This was after adding all the water. What can I do to hit close to the temps I want at a reasonable mash thickness?

How thin is the first rest?

Have you considered performing a decoction instead of a water infusion to raise mash temps?

joety said:

How thin is the first rest?

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Last time I did a 1-1 dough-in, right now I'm doing an oatmeal stout and the 1-1 looked too thin to me and I ended up with a 1.3 qt/lb dough-in.

KellyK said:

Have you considered performing a decoction instead of a water infusion to raise mash temps?

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I've done one decoction with similar results, sacc rest temp about 10 degrees low with the prescribed volume

Well, I've done a step-mash just once, and I'm pretty sure I started at only 1 qt/lb (maybe even .85). I just barely got the second strike water up to temp before the first step was scheduled to end, but otherwise it went flawless. Next time I'll use more pots.

What you need is software that accounts for the thermal qualities of your specific mash tun. For example, beer tools pro has a calibration step that teaches the software what the heat capacity of your tun is. Therefore, it takes that into account when you want to change temps.