Interpreting single-infusion mash instructions with two temperatures listed

Question

I've been brewing all-grain for a while now, but I can't figure out why the recipes I read have the following. Take this example:

Mash Schedule: Single Infusion, Light Body
Total Grain Weight: 10.25 lb (4.7Kg)
Single Infusion, Light Body
Step Time Name Description Step Temp 
75 min Mash In Add 12.81 qt of water at 163.7°F 152.0°F 
10 min Mash Out Add 8.20 qt of water at 196.6°F 168.0°F 
Sparge with 2.64 gallons 168.0°F water

Why do the Mash In and Mash Out have two different temperature readings if it's single infusion? Did the brewer mash in at the first temp (in this case 163.7°F/73°C) to get to the second temp (152.0°F/67°C)? This is what is seems to me, yet if that is the case I don't think mashing out at 196.6°F would get to a final temp of 168°F. In any event, if someone could clarify this for me it would be appreciated!

Answer 1

The first temperature is of the water you are adding while the second is the expected temperature of the mash after it has been added.

So by adding 12.81 qt of water at 163.7 F to the grain (presumably at room temp) the mixture should land around 152 F. Mashing out is an optional (though common) step that is meant to bring the mash above the temperature range where the enzymes at work in the mash are no longer active. Which is why this wouldn't be considered a second infusion; it's more like force-stopping the mash by increasing the temperature.

Here by adding 8.20 qt of water at 196.6 F the mash overall should end up at roughly 168 F which is a pretty normal mash out temperature.

Ultimately, you have an infusion at 152 F and mash out to 168 F. You just get there by adding water in two steps of 163.7 F and 196.6 F respectively.