Author Topic: Original Gravity Problems  (Read 1473 times)

Offline bruck

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Original Gravity Problems
« on: January 17, 2010, 06:24:06 PM »
OK...So I can't figure out what's going wrong. I have about 70% efficiency into the boiler consistently. Really no problems there, but today got 56% efficiency after the boil. My efficiency is not always that bad, but never what I would expect. I have been using a straining bag for the hops lately that I am wondering about, but other then that I really can't figure out what the problem could be. Thoughts?

Offline Thirsty_Monk

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Re: Original Gravity Problems
« Reply #1 on: January 17, 2010, 07:59:23 PM »
pH issue would be my bet.

You did not say what you brew (SRM) and what is your RA. Any water adjustments?
WHat do you normally brew?

Another thing. Did you change your base grain let say from 2-row to Munich?
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Offline a10t2

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Re: Original Gravity Problems
« Reply #2 on: January 17, 2010, 09:37:33 PM »
So you're at 70% going into the kettle, but 56% in the fermenter? That would be right on if you were leaving 20% of the wort in the boil kettle, which seems unlikely.
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Offline bruck

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Re: Original Gravity Problems
« Reply #3 on: January 18, 2010, 07:52:15 AM »
Only leaving about a half gallon in the kettle. With regards to PH, I use the 5.2 treatment in the mash so I'm not sure that is the problem. With regards to the grain, it was just a standard mix of 2 row, crystal and wheat malts. Could I still have PH issues even after using the 5.2? Again, the gravity into the boiler was good.

Offline Kaiser

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Re: Original Gravity Problems
« Reply #4 on: January 18, 2010, 08:28:05 AM »
When you calculated the efficiency into the kettle, did you correct the volume for temperature?

Leaving behind .5 gal when collecting 5 gal in the fermeter is a loss of about 10%. I.e. you should get about 90% of your “efficiency in the kettle” into the fermenter.

Kai

Offline nyakavt

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Re: Original Gravity Problems
« Reply #5 on: January 18, 2010, 08:29:18 AM »
The only difference in efficiency between the beginning and end of boil is the amount of wort you leave behind in the kettle.  You have a measurement error either on the volume or the specific gravity, or both.  How are you measuring each?  You also must account for water being less dense at higher temperature, so if you take your pre-boil volume measurement at boiling it's actually 4% smaller than that.  Not enough to make up the discrepancy, but it's still important.

Offline bruck

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Re: Original Gravity Problems
« Reply #6 on: January 18, 2010, 08:41:51 AM »
I did correct for temperature. In fact, I checked the gravity not only with a hydrometer, but also with a refractometer. I was really surprised to see such a low efficiency...

Offline nyakavt

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Re: Original Gravity Problems
« Reply #7 on: January 18, 2010, 08:51:44 AM »
How did you chill the pre-boil gravity sample prior to measuring?  There can be a lot of evaporation when cooling a small sample, so you need to do it in a sealed container to get an accurate measurement. 

If you are sure about the gravity reading, what about the volume? How was it measured?  You need to have a very accurate way of measuring volume if you intend to compare efficiencies batch to batch.  If you don't, then you could easily see a 5% swing just from measurement error.

Kai is right, if you leave behind 1/2 gallon in a 5 gallon batch you'll only get 90% of the efficiency you got 'into the kettle', or 63% if you had 70% in.

Offline bruck

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Re: Original Gravity Problems
« Reply #8 on: January 18, 2010, 09:17:44 AM »
I have volume increments labeled on all of my carboys. I think that the volume is accurate. Could the wheat malt have had anything to do with it? I have only used wheat malt in the past when I have made wheat beers.

Offline Thirsty_Monk

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Re: Original Gravity Problems
« Reply #9 on: January 18, 2010, 09:20:58 AM »
No I do not think so. 
Wheat malt has normally higher extract potential than barley malt.
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Offline a10t2

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Re: Original Gravity Problems
« Reply #10 on: January 18, 2010, 09:26:28 AM »
I have volume increments labeled on all of my carboys. I think that the volume is accurate.

I think this is (most of) the issue. If the volume markings on your carboys are from the manufacturer, don't assume they're accurate. IME, they aren't.

Separate issue, but the 5.2 buffer will only work if your pH is already close to 5.2. But if your pH is "close enough", you don't need to use it.
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Offline bruck

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Re: Original Gravity Problems
« Reply #11 on: January 18, 2010, 09:49:41 AM »
I actually made the markings myself so I am sure they are accurate. With regards to PH, wouldn't my preboil gravity not be good either if that was a problem?

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Re: Original Gravity Problems
« Reply #12 on: January 18, 2010, 10:07:54 AM »
Could I still have PH issues even after using the 5.2?

You sure could....never assume that stuff is working for you, always measure the pH.  But sine you were OK into the kettle, I really doubt it's a pH issue.  It's more likely a wort loss issue somewhere.
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Offline bruck

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Re: Original Gravity Problems
« Reply #13 on: January 18, 2010, 11:05:55 AM »
Do you think that maybe the hop bag that I was using could be the culprit? I let it drain out before I took it out of the kettle, but I wonder if that is contributing to some gravity loss.

Offline a10t2

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Re: Original Gravity Problems
« Reply #14 on: January 18, 2010, 11:46:22 AM »
Not unless you're losing half a gallon to hop absorption.

Sorry, but I think one or more of your volume/gravity measurements has to be wrong.
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