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Old 02-15-2009, 04:46 PM   #1
cladinshadows
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I just finished brewing two small batches (my second and third AG) and I took some conflicting efficiency/gravity readings. Hopefully someone can help me come to the "duh" moment... I feel like I'm missing something obvious, but I'm too stupid to figure it out.

For both batches I used a single-infusion mash for 90 min. at 152F with 1.25 qt/lb of grain, then batch sparged at 170F with 2.5 lb/qt.

For the first batch, I expected to collect about 4 gallons of 1.034 wort, assuming 70% efficiency. I conducted the mash, everything seemed to be going well, hit my temps, etc. Once everything was ready to begin the boil, I took my volume and gravity measurements... I had 4 gallons of 1.040 (took my reading at 154F, measured 1.020), meaning I hit 80% efficiency. Alright! Off to a good start!

Or not. After I finished my boil, cooled the wort with my brand new IC, got it into my carboy, took my reading... I had collected 2.75 gallons of 1.045 at 70F, meaning efficiency of 64%. What gives!? Where did I lose it?

Next batch I performed the same mash, hit all my temps, everything looked good again. This time, I assumed that one or more of the following things may have happened to my last batch:

1) Didn't mix my sparge water and wort very well, so my first reading was not indicative of the actual boil volume once mixed,

2) The temperature of my reading was high enough to introduce some serious error when calculating the gravity.

3) I had too much of my last batch in me and reading the hydro was just too much to ask.

So this time, I took 7 readings (I wasn't worried, just concerned) at various temperatures, mixed everything reasonably well, and double checked a few with SWMBO. The lowest reading I got was that I had collected 4.25 gallons of 1.036, meaning 78% efficiency. OK...

Sure enough, like the time before, I collected a final volume of a little less than 3 gallons of 1.044 wort. That means my efficiency was more like 65%.

So HBT, where did I go wrong?

I can post the recipes if that will help, I just figured this post was long enough already.

 
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Old 02-15-2009, 06:58 PM   #2
ajf
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Your suggestion 1 is a common mistake. It requires a really good stir to get everything mixed.
Suggestion 2 is also valid. Even if you use temperature corrections, hydrometer readings are very unreliable at temperatures over 100F or so.
I think the problem really occurred by taking the first reading from the kettle, and the second reading from the fermenter. This would only give you the same efficiency if you drained every single drop from the kettle into the fermenter, but you will lose some efficiency to hop absorption (especially if using whole hops), dead space in the kettle, and trub that got left behind.
What you are seeing is the difference between mash/lauter efficiency and brewhouse efficiency (which takes these losses into account).

-a.

 
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Old 02-15-2009, 07:35 PM   #3
cladinshadows
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I dumped nearly everything into the carboy, including the vast majority of the break material (I probably left 2 cups of material behind, out of a nearly 3 gallon batch). Could the small amount of hop and break material that I left behind really have affected my reading that drastically?

 
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Old 02-16-2009, 01:16 AM   #4
ajf
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Well, 2 cups would account for about 4%. Also, if you transfer the break material and hop debris into the fermenter, that solid matter will be saturated with sugar rich wort that won't show up in the OG. However, as the trub settles out, some of the sugars will be released into the beer to be attacked by the yeast. (OK, that may not be true, but it makes sense to me.)
Are you absolutely sure about your volume measurements? A small over estimate of the pre-boil volume, combined with a small under estimate of the volume in the fermenter can combine to produce a large percentage drop.

-a.

 
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Old 02-16-2009, 02:57 PM   #5
cladinshadows
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Well, I'm as sure as I can be short of measuring it out cup by cup (I know the inside diameter of my pot and I just measure the depth of wort). Oh well, it'll still be beer when it's done....thanks for your help!

 
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Old 02-16-2009, 06:10 PM   #6
Bobby_M
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Volume measurement errors can easily add up and yes hydrometer temp corrections are questionable. Chill your samples and make sure you know your volumes. Calibrate your fermenter by dumping a gallon in at a time and marking with a sharpie. When you get to 4.5 gallons, do it in 1 quart increments up to 5.5g.
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