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Old 04-24-2009, 12:17 PM   #1
DD2000GT
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Default Question about brewhouse efficiency and FG

I just brewed my 2nd AG batch - an Irish Red kit from Midwest. It had 9 lbs. of 2-row, .75 lbs. of crystal, and .50 lbs. of specialty grains. The kit showed I should have a FG between 1.042 - 1.046. I ended up with 1.052 but Beersmith only showed me with a 71% brewhouse efficiency going into the fermentor. I had 77% efficiency into the boiler - not really sure how I can have a higher efficiency into the boiler but lower on the final - but whatever.

So - does this mean Midwest expects 65% or lower efficiency, or am I looking at my efficiencies wrong?

The specs - I had a 1.042 gravity going into the boiler with 6.75 gallons of water from the grain bill above, and had a 1.052 gravity going into the fermentor with 5 gallons of water after the boil.

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Old 04-24-2009, 12:29 PM   #2
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Did you correct your volumes for temperature? That would account for some of it. If you measure 6.75 gal. @ ~170 then you really only have about .97*6.75=6.55 gal and if it's near boiling you only have .96*6.75=6.48 gal. And make sure you read the hydro samples at cool temps...there's too much error reading them warm and correcting.

There is also the issue of how you measure the volumes. If you measure one in a kettle and another in the fermenter then those two volume measurements must both be accurate...any little error of one or the other will skew the calculations.

And you should expect some sort of very small boil loss to wort absorbed by hops, trub, splashing/dragout, etc. but this shouldn't be much.

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Old 04-24-2009, 12:36 PM   #3
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Spanish - I did not adjust for temps - I used exactly what I measured. I measured the water going in with a measuring pitcher - so I know the volumes were dead on. Can you explain a bit more how 6.75 gallons of wort at 170 degrees is truly 6.55 gallons - I am lost there.

Also - I always take my hydrometer readings at 60+- degrees. I put the sample in the fridge and mix it back up good before taking the reading. Sometimes I am off a few degrees and have to adjust, but not much.

I never really "measured" the volume in my fermentor. I use an old glass carboy that says 5 gallons on the bottom - but to be honest I have never truly measured the volume. I might try that once the Red is out of it in a few weeks.

Dan

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Old 04-24-2009, 01:35 PM   #4
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Water expands as it heats so when you measure your volume at high temps you have to adjust. It's the same reason you have to correct your hydrometer readings for temp because if water expands as it heats then the density must go down causing the hydrometer to 'sink' a little more than it would at it's calibration temp.

So you just multiply the volume measurement by .97 if it's @ lauter temp (~170-ish) or by .96 if it's near boiling.

The volumes you measure must be accurate in order to get accurate efficiency calculations. Make sure when you measure 5 gal. in your carboy that it matches exactly with 5 gal. measured in your kettle. Using a pitcher can cause you to stack up a bunch of small errors leading to one big error by the time you get to 5 or 6 gallons...so if possible see if you can get an exact gallon measure and then 'calibrate' everything to that.

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Old 04-24-2009, 02:11 PM   #5
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Gotcha. Using this theory then, my efficiency into the boiler would actually be better than recorded as it was 1.042 gravity to 6.55 (adjusted) gallons instead of 6.75 gallons.

Correct?

EDIT - forget that - it is the other way around. My efficiency would be worse if I had the same 1.042 gravity with less water...

Not sure why I am getting such good final gravities with such low efficiencies.

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