93% efficiency?

[Demus]

The consistent is probably more important than the 80%. Whatever it settles out to be, keep in mind it will fluctuate somewhat based on the recipe. If you work in gravity points the boil off/original gravity numbers are simple to figure. It's easy once you've done it a few times. Basically you just subtract 1.0 (the gravity of water) from your gravity reading. Say it's 1.070, you have 70 points per gallon. If you're sparging away and have 6 gallons, that's 420 points. If you stop there and fire up the kettle and boil it down to 5 gallons, what will your OG be? Simple, the points don't change because ONLY water boils off. Divide your 420 points by your new volume of 5 gallons. 420/5=84. Add back your 1.0 for water and you've got 1.084. It's even more convenient the other way. Say you're brewing a 1.060 APA. You want a 5 gallon batch with a one hour boil and boil off 1 gallon per hour. First, how many points do you need? 60x5=300. Next, what gravity will your 6 gallons have to be for 300 points? 300/6=50, or 1.050. With a refractometer, it's easy to take many readings as you go. So, if you get 300 points before your diaries volume is reached, you have a choice to make. You can stop the sparge and top up to desired volume with water, you can make more 1.060 beer, or you can make higher gravity beer. On the other hand, if you get to 6 gallons and have not reached 300 points, your choices are different. You could settle for lower gravity, add DME/LME, or continue to sparge until you get to 300 points. If you continue, you'll simply have to lengthen the boil to account for the extra water.
I think you'll agree that the first scenario (getting desired points early) is easier to deal with. If you want MAXIMUM efficiency all the time, you might be dealing with the second scenario quite often. Saving a few bucks is cool, but saving a few hours is better!

 

[ssgross]

it seems that everyone is assuming the sight glass on the blichmann pot is accurate. while I believe that blichmann didn't lie when they wrote "calibrated to within +- 1 quart", I do not know what temp the liquid was when it was calibrated. if they used water at 70F room temp, and you are measuring 10 gal. at 212F at the beginning of the boil, then you are recording an extra .43 gals because water volume goes up 4.3% between 70F and 212F.

The ProMash documentation include interesting information on the differences in how efficencies are calculated in different settings. In particular, the way breweries calculate efficiency according in a way that high numbers will be rare. for the homebrew calculations, higher numbers are common since they include values for each malt as reported by the malsters, or as entered by you based on practice.

The point is, the numbers are meaningless without context of their calculation. For me, I know my process is sound, regardless of the calculation. I care about the efficiency calculation I use (first by hand, later I used ProMash homebrewer settings) because I care about the consistency of my process from one batch to the next, and repeatability in the beers I consider mastered (according to my own palate). If my numbers are consistent, then I can alter recipes and determine exactly the cause of the new outcomes. By consistency in my process, I learn some very precice information about what changes might effect the final product and how.

Certain homebrewers (none of you all ) annoy me when they tout their mash efficiency number as a "Mine is bigger than yours". For the "high efficiency = tannin off flavor taboo police" people. Your equation/prediction is meaningless since it depends entirely on how you calculate efficiency. I measure Ph all the time and never come close to the Ph and temp where this would happen, and I get "91%". See rant above about the purpose of my calculation. I will close with giving my own "mine is bigger than yours" quote. My efficiency is calculated at 91.4% +- 0.2% for every brew. I never miss a target gravity by more than +- .0009. +-.0005 is the margin of error of my lab grade hydrometer, and the other .0004 I assume comes from the variability of malt quality. On a small scale (10 gal batches) and with careful measurements, you can hope for the same as well. Sorry I am in a of a mood. I hope I added perspective on the efficiency debate. Cheers.