In everything I've read, from books to forum post everyone says to sparge at 170 F, but nobody says why it's done this way. I was going to brew a Imperial India Pale Ale and from what I understand the mash should be done at a low temperature to avoid sweet flavors. If this is the case, shouldn't the sparge be done at a lower temperature, too?
The purpose of the mash is to convert starches to sugars. What types (molecular lengths) of sugars are "created" in the mash is determined by the temperature. Generally speaking, the lower the temperature the *simpler* (more easily) fermentable the sugar. That is why a higher mashing temp will generate more complex (less easily fermentable) sugars and most likely give you a sweeter beer, due to the residual sugars which the yeast is incapable of fermenting. More info here: http://www.howtobrew.com/section3/chapter14-1.html The purpose of sparging, on the other hand, is primarily rinsing the converted sugars out of the grains. And this is most effectively done at a somewhat higher temperature. See: http://www.howtobrew.com/section3/chapter17.html If 170 is actually the ideal and/or max temp, is a matter of quite a bit of discussion. (e.g. http://www.thebrewingnetwork.com/forum/viewtopic.php?f=2&t=10782) I have sparged a bit colder, and had the feeling that my efficiency wasn't very good, and I have sparged a number of times at closer to 175 without noticing any ill effects. So, I will be sticking with 170-175, but YMMV.
Ok, Ok. I can see what the logic is behind it. I've never done it any other way, you have, thanks for the insight.
SBA pretty much covered it. Extraction of tannins is a bigger concern at that stage than excessive sweetness - just make sure your ph stays in the low 5 range and stop sparging at 1.008 - 1.010. As he said, the idea is just a more effective sugar rinse.
Yeah I am going to 2nd the tannin extraction. I know people that go at about 168 to not risk getting too high on the temp and extracting tannins. I usually sparge until I hit my volume and don't pay much attention to the 1.008 rule but that's just me... Most mashing generally is between 148 and 156. 148/149 being the more fermentable temps, 150 to 153 being a good mix in the middle and generally acceptable for all styles. 154 to 156 is the less fermentable sugars. The different temps kick in different enzymes.
