Right, is the bump in efficiency due to the temp rise, the stirring, the longer mash . . . all of them? I haven’t tested it rigorously, and I suspect most people haven’t either.
Based on Kai’s experiments using cool water to sparge without an efficiency loss, I’ve come to believe that efficiency increases due to adding hot water to the mash happen because of increased conversion from the hot water.
Are there other cold water sparge experiments that Kai or yourself ran, or is it just the one that’s posted on his site?
I’m pretty sure the only one Kai has done is on his website. I didn’t do ant formal experiments, but I did try sparging with 60F water a couple times just to see what happened. I got the same efficiency that I do when I brew that recipe with hot sparge water. In that recipe, even using hot sparge water, the mash temp never gets above about 158.
Interesting. That’s not at all what I, or a fellow brewer experienced. Oh well, I’ll stick with something that I know works.
I’m definitely not planning on making sparging with cool water a regular part of my brewing! I was just curious about what would happen.
It would just take that much longer to come to a boil. 
Yep. It’s not a practical thing to do. Just an experimental exercise.
I think it would simplify my process to use cool sparge water - I wouldn’t have to use my kettle as an HLT during the sparge, and I wouldn’t have to deal with heat loss from the sparge water. Maybe I’ll give it a try. Any reason not to use cool water for sparging, assuming there’s no impact to efficiency and that I wouldn’t mash out anyway?
Well, for me I would heat it anyway so it would boil faster, but if that doesn’t bother you then it’s worth a try.
Tom,
That is a very good point, mashing out is providing an additional heat input that we’ll need eventually to boil. Mash out just makes sense to me.
Devil’s advocate here: It seems that you’re heating either way; whether you heat to mash-out or heat the sparge water you’re still heating the entire grain bed which ends up being ‘wasted’ heat because much of that heat remains in the grain bed. When just heating the kettle up to the boil you’re not devoting all that ‘thrown away’ heat to the grain bed.
I mash-out and sparge hot, just making the point.
Yes, but if you sparge with cooler water, your efficiency will suffer a little. If energy conservation is more important to you. then your point is well made.
The efficiency thing was covered earlier itt. It seems to make a difference for some and not for others. I’m not really worried about a slight difference in efficiency (grain is cheap) or a slight difference in propane use (it’s a drop in the bucket since I already use a lot). Like everyone else here, I just want to make the best beer I possibly can. But old habits die hard (so I still mash-out and sparge hot).
Sure, some heat remains behind in the mash, but more ends up in the mash tun. This would vary depending on how you mash of course, fly spargers tend to leave more water behind in the mash than batch spargers.
Not only are you not adding more heat to the mash, you are actually moving heat from the mash to the boil kettle. The 60* water you sparge with comes out the other end at 60* + some, depending on the heat of the mash when you add it. I tried this a couple of weeks ago because I forgot to heat my sparge water before starting my sparge so I just dumped it in at like 90 or so (didn’t take it’s temp) didn’t seem to hurt my eff but I am not that exacting so who can say.