CBBaron

Recipes 

There is some complexity in calculating expected efficiency with this system.
First the first mash step should yield you the same efficiency you would get with a normal beer as that is the wort you are producing.
For the second mash the first runnings should be very high after dissolving the additional sugars in the new grain into the already rich wort leaving behind about 1.8 gal (10# * .18gal/#) of rich wort. You then sparge this grain bed with a similar volume of water to make up for the water left in the grains. Which leaves you with 1.8 gals of wort with half the gravity of the first runnings in the grains.
For the third mash you get a similar situation only with an even higher gravity. So the inefficiencies of the system are the combination of the worts left in the 30# of grain.
If you mash 30# at one time you leave about 5.4 gal of wort at the gravity of you last runnings. For a big beer with a 60 min boil you are going to sparge 30# with 3-4 gals so the last running are going to be pretty high G.
For 3 iterations it is going to be 1.8gal at the low final runnings of the first mash + 1.8 gal at the higher final runnings of the second mash + 1.8gal of the even higher final runnings of the third mash.

I think I can use the formulas from Kaiser and estimate a best case efficiency. I'll think about doing that this evening. I'm curious if 1, 2 or 3 mashes is optimum for a 5gal beer with 30# of grain and a 6.5gal starting boil volume.

I have a interest in reiterative mashing because I have a 5gal mashtun and I'm curious if reiterative makes more sense than multiple regular mashes.
Craig

Kaiser

Recipes 

I think you can go even a step further and calculate how close your actual batch sparges have come to the theoretial maximum and use that number of get an actual efficiency estimate from the theoretical maximum that you get for reiterative mashing.

Another benefit of reiterative mashing might actually be the fact that you can get better fermentability by keeping the last mash really low for a long time. This allows the beta-amylase, that has just been added, to produce lots of maltose. You will then need to step it up to convert the rest of the mash.
Kai

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CBBaron

Recipes 

Good idea I keep that in mind.
That assumes you want a more fermentable wort. I like my big beers chewy.
Well maybe not always but it is something to consider.

I also plan on running some calcs with lower volumes for the first mash which fits better with my system (I can't fit 6 gal of mash water and 10# of grain in a 5gal cooler). My gut feeling is that using a lower volume after the first mash will trade off extraction efficiency from the first mash for improved extraction (greater sparge volume) for the second mash, resulting in slightly better results because the wort gravity is higher in the second mash.
Then of course I'm going to have to experiment to show that my numbers match reality.

Craig

explosivebeer

Recipes 

I'm glad people seem to find this concept as interesting as I did. I'm definitely curious to see how it turns out, or hear other peoples' experiences with it.

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Kaiser

Recipes 

I updated this graph to make the lines stop when the water/grist ratio is less than 1 qt/lb which makes for an unrealistic sparging scenario. Given this information, only a no-sparge is realistic for a 30 lb grist and there you will get 62% max efficiency.

Kai

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BrauKaiser.com - recipes - Blog - German Beer Reviews - Water and mash chemistry spreadsheet