Step up: Direct heat or boiling water additions?

[brick]

In a couple weekends I'm planning to do my first step-up mash. I'll be using 35% rye malt so I'd like to do a beta glucan rest before heading for saccharification. Thing is, I have two choices and not enough experience to decide between them: Mash in my 10gal Igloo and add boiling water to get from ~110F to ~153F, or mash in the boil kettle on the stove and transfer to the Igloo for lautering. Here's how I see it:

-If I mash in the Igloo I can start thick (<=1qt/lb) and end up thin but reasonable after the boiling water additions (~2qt/lb) which is OK. But I'm a little worried about the effect of adding ~3gal of really hot water on enzyme denaturation and tannin extraction. (Some portion of the mash will be exposed to way high temps between many iterations of pour/stir.)

-If I mash under direct heat, I guess the only down-side is that I'll have to physically transfer 12lb of grain and 4-ish gallons of water from the brew pot to the Igloo, which will take some extra time. On the plus side, a lower volume of water in the mash (since I don't need to add water to add heat) means a better sparge volume.

Right now I'm inclined to suck it up and mash in the brew pot, but I'm curious what you would do. Opinions?

 

[moonmandave]

Great question. I've been wondering the same thing for the Belgian White I'm making in a few days.
I'm worried about pouring in mega hot water, but I'm sure if it's added in conservative amounts, you could stir it in, and still have plenty of time for the grain bed to settle again before you run the wort out.

 

[Yooper]

It doesn't matter. When I had a cooler for an MLT, I mostly did infusions or decoctions for step mashes. When I got a keg with a HERMS, I recirculated to ramp up the temperature.

With direct fire, the biggest issue is overheating and scorching/burning your grain or wort. There isn't any down side to infusions, though. Adding boiling water wont' harm the mash- after all, you will be stirring and the idea is to raise the temperature to 153 (or whatever your saccrification rest temperature is).

 

[brick]

Thanks for the feedback. The point about scorching is a great one, and from that perspective it's hard to argue that slow boiling water additions are any more risky. I think I've discounted the sparge volume argument, too. I figure I can just sparge until the runnings come out at a reasonable gravity and boil longer up-front if starting volume is higher than I wanted.

Guess that's settled! I'll give boiling infusions a shot.