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Old 04-02-2008, 09:54 PM   #1
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Default my efficiency numbers are wack!

i'm having some trouble figuring out what's going on with my efficiency. i made a maibock on sunday with 13lbs of grain. i start with 8.75 gallons in my kettle and boil down to 6 gallons. i ferment 5.75 gallons. i always nail my volumes. with my efficiency set at 85% beersmith said that my estimated OG is 1.067. after sparging to my boil volume my pre-boil gravity was 1.045, which gave me a pre-boil efficiency of 82.7%. after boiling and hitting my volumes my OG was 1.057, giving me an actual efficiency of 71.83%. what's the deal? what am i missing? i've read the wiki and all the posts about efficiency and i still don't get what i'm missing.

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Old 04-02-2008, 10:25 PM   #2
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eagerly awaiting a response to this question, I have asked but never really gotten a good explanation that I can understand (pics with crayon would help)

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Old 04-02-2008, 10:39 PM   #3
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My guess is that there are a number of things going on, all of which add up to your final efficiency being lower than you would expect.

First, there are the volumes. If your pre-boil volume is a bit lower than your estimate, that would account for something, and if the post boil volume is higher, that would account for a bit more. How do you measure your volumes? Using Ale Pales is notoriously inaccurate. If you have a good scale, weight could be more accurate.
Next, there is the temperature correction on the gravity readings. These are usually failrly accurate with temperatures below 80 - 90 degrees, but can be wildly inaccurate at sparge temperatures.
I'm guessing that you measured the 1.057 after transferring from the kettle to the fermenter. Was there anything left in the kettle after transferring to the fermenter? I have to leave a bit behind in the kettle, and the wort chiller. These will adversely affect efficiency.
Where did you get the sample to measure the OG? Was it taken from the 6g transferred to the fermenter, or was it in addition to the fermenter volume?
Then, did you take the OG reading after adding a starter? The starter will have a lower gravity than the wort, and will lower the OG when added.
Lastly, you will get some wort absorbed by the hops during the boil. This can be quite substantial if you use whole hops, and this will result in a decrease in efficiency.

Hope this helps.

-a

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Old 04-03-2008, 01:48 AM   #4
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where to start . . .

Quote:
Originally Posted by ajf
First, there are the volumes. If your pre-boil volume is a bit lower than your estimate, that would account for something, and if the post boil volume is higher, that would account for a bit more. How do you measure your volumes? Using Ale Pales is notoriously inaccurate. If you have a good scale, weight could be more accurate.
Quote:
Originally Posted by SenorWanderer
i always nail my volumes.
Quote:
Originally Posted by ajf
Next, there is the temperature correction on the gravity readings. These are usually failrly accurate with temperatures below 80 - 90 degrees, but can be wildly inaccurate at sparge temperatures.


Quote:
Originally Posted by ajf
I'm guessing that you measured the 1.057 after transferring from the kettle to the fermenter. Was there anything left in the kettle after transferring to the fermenter? I have to leave a bit behind in the kettle, and the wort chiller. These will adversely affect efficiency.
Quote:
Originally Posted by SenorWanderer
i start with 8.75 gallons in my kettle and boil down to 6 gallons. i ferment 5.75 gallons.
Quote:
Originally Posted by ajf
Then, did you take the OG reading after adding a starter? The starter will have a lower gravity than the wort, and will lower the OG when added.
no.

anyone else?
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Old 04-03-2008, 03:33 AM   #5
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"However, the main drawback to refractometry is that natural temperature variations in the sub stances being measured result in grossly inaccurate refractive readings."

In the information I could quickly find, there aren't even correction factors past 40C.

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Old 04-03-2008, 03:41 AM   #6
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that's interesting, didn't know that. my refracto has Automatic Temperature Correction, whatever that means. i always let my sample sit for a few minutes to let it "absorb" the temperature of the refracto, so i doubt that this is a concern.

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Old 04-03-2008, 03:52 AM   #7
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Do I detect a note of sarcasm and disdain? Sorry, next time I'll use my psychic powers to learn all about your equipment and setup before I try to help. Oh, and your keys are under the table.

Anyways, short of losing some wort somewhere, somehow, or boiling it over and since your volumes are spot on - one of your gravity readings is wrong. I was just thinking the temperature could be the culprit. The sugars aren't going to just disappear - and if they are, you've got bigger problems, or something you need to patent!

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Old 04-03-2008, 04:02 AM   #8
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I didn't run the numbers but you're admittedly losing a quart to trub or something else between the kettle and the fermenter but that's not enough to drop your brewhouse by 10%.

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Old 04-03-2008, 05:09 AM   #9
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Sometimes I just don't care what the efficiency is because I get good numbers anyway. If you want accurate results then everything has to be calibrated and measurements must be accurate for volumes and temperatures plus correction.
Be sure to mix well before taking a gravity measurement.

Inaccurate in = bogus numbers.

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Old 04-03-2008, 06:25 AM   #10
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sorry tentacles, no sarcasm to your answer. i am really frustrated because i am very precise when it comes to things like gravities and volumes.

bobby, i am leaving behind a quart, but that's on purpose. when i calculate a recipe in beersmith i set my batch volume to 6 gallons knowing that i'll leave a quart in the kettle.

i guess now is where i go in depth about process. . .

like stated before, eff set to 85%, and my eff. into boiler is always right around 85%, often pushing 90%. i sparge to 8.75g to boil down to 6g over 90min. after vorlaufing into a 1g pitcher graduated to pints i drain all my runnings into a 5 gallon bucket and then measure off the runnings in my 1g pitcher before pouring into the kettle. my volumes are insanely accurate. yes, i've actually boiled off a bunch of water to figure my boil loss. i ferment 5.75g in a 6.5g carboy, purposefully leaving a quart in the kettle to leave behind hops and break. once i've filled my carboy to 5.75g the leftover in the kettle is very thick with hops and break and crap and there is some liquid visible, but not nearly enough to account for the discrepancy. my carboys are marked off from 5g to 6g in 1 quart increments. i take the sample for my pre-boil gravity before the wort comes to a boil, and i take my sample for post boil OG from the full carboy, just after it's filled, and before it's aerated or pitched.

so is what all of you are telling me is that if my pre-boil volumes and gravities are accurate and my post-boil volumes are accurate then my post-boil gravities should result in matching efficiencies?

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