Author Topic: final gravity measurements?  (Read 6877 times)

Offline Johnnyv42

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final gravity measurements?
« on: November 20, 2011, 12:22:03 PM »
I just checked the gravity of my Wee Heavy and it's much lower than my target. My recipe targeted 10% ABV and I'm only at about 7.5% :( I've not had this problem with previous batches of beer. I usually nail the ABV target right on the head. I'm wondering if my measurement is being fouled by the suspended particulate (yeast). When I taste it, it sure taste like a higher ABV than 7.5%, but that's so subjective (malt/hop/ethanol balance...). I've measured the gravity 2 different ways, using both my refractometer and my hydrometer, and get the same results. Is it possible that the suspended particulate/yeast are causing both tools to measure the gravity high?
Primary: Wit, Red

Secondary:

Bottled: Brown, Coffee Stout, Stout, Wee heavy, 60 Shilling, Brown Ale, Smoked Black IPA, American Pale Ale, Vanilla Porter, Wit

Offline MaltLicker

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Re: final gravity measurements?
« Reply #1 on: November 20, 2011, 04:49:53 PM »
Looking at what you've recently bottled, how often do you do 10% ABV brews?  Lautering efficiency drops with larger grain bills; if you did a 10% beer as all-grain, perhaps that was the issue? 

And with a wee heavy, one technique to boost the gravity is by a very long boil, so one does not have to collect all the OG from the grains. 

For ex, you may collect 1.085 and boil it down to 1.105 or so.  That also creates the caramelization flavors of the style. 

Offline tom_hampton

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Re: final gravity measurements?
« Reply #2 on: November 21, 2011, 03:05:37 PM »
I think he's talking FG (not OG). 

10% is a strong beer.  Fermentations will stick or slow down as you go up in ABV%, and OG. 

How much yeast did you pitch?  You would have needed a LARGE starter for that beer: 4-ish liters without a stirplate, 2-ish with one.  Careful yeast selection is important, too.

Has your FG stopped moving?  If so, you can try to rouse the yeast: GENTLY stir it back into suspension. 

What temp are you fermenting at?  You can also try to warm it up some.  Warm slowly (a degree per hour is about right) to over 70F, you can probably go as high as 75F at this stage....depending on your yeast strain.
R.I.P.:Belgian Blonde
On Tap: Apfelwein, Kolsch(v2), Pumpkin Ale, Belgian Specialty 
Aging/Storing: Coffee Porter, Chocolate Porter, Flanders Red, English Barlywine
Fermenting: Maggie's Altbier
Next Up: PtE(1.1), Belgian Dubbel?

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Offline Johnnyv42

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Re: final gravity measurements?
« Reply #3 on: November 21, 2011, 05:21:26 PM »
Thank you for your responses. Unfortunately, you're responding to a question I didn't ask. If the ABV is only 7.5% I have several ideas why that might be. My question refers to the measurement process itself, not the results of the measurement. I wouldn't be surprised if this beer didn't ferment as much as I would have liked. But I want to make sure that the cloudy beer isn't distorting the measurement some way. So, let me ask the question:

Does suspended particulate/yeast affect the refractometer measurement, does it affect the hydrometer measurement?

Primary: Wit, Red

Secondary:

Bottled: Brown, Coffee Stout, Stout, Wee heavy, 60 Shilling, Brown Ale, Smoked Black IPA, American Pale Ale, Vanilla Porter, Wit

Offline tom_hampton

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Re: final gravity measurements?
« Reply #4 on: November 21, 2011, 05:42:56 PM »
Quote
Does suspended particulate/yeast affect the refractometer measurement, does it affect the hydrometer measurement?

No.  Or rather, at the risk of providing to much detail, not enough to matter.
R.I.P.:Belgian Blonde
On Tap: Apfelwein, Kolsch(v2), Pumpkin Ale, Belgian Specialty 
Aging/Storing: Coffee Porter, Chocolate Porter, Flanders Red, English Barlywine
Fermenting: Maggie's Altbier
Next Up: PtE(1.1), Belgian Dubbel?

Working thru all BCS recipes

Offline Johnnyv42

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Re: final gravity measurements?
« Reply #5 on: November 22, 2011, 04:17:58 PM »
Detail? I like detail.  :) One of the things I like most about brewing is learning all the details. Would you like to share those unmentioned details? ...or at least a link to them.

Thanks!
Primary: Wit, Red

Secondary:

Bottled: Brown, Coffee Stout, Stout, Wee heavy, 60 Shilling, Brown Ale, Smoked Black IPA, American Pale Ale, Vanilla Porter, Wit

Offline Myk

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Re: final gravity measurements?
« Reply #6 on: November 22, 2011, 04:38:04 PM »
One detail is a dirty sample on a refractometer settles on the prism and blurs the line making it hard to read accurately.

That "feature" is one way to test corn for ripeness. Turn it upside down and the starch settles on the lid. But I found in brewing it's not a good test of conversion by comparing to iodine.

Offline tom_hampton

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Re: final gravity measurements?
« Reply #7 on: November 22, 2011, 09:25:53 PM »
Detail? I like detail.  :) One of the things I like most about brewing is learning all the details. Would you like to share those unmentioned details? ...or at least a link to them.

Thanks!

Dry weight of 20 billion yeast cells = 1gram.  A finished 5 gallon batch develops about 900 billion yeast cells = 45 grams = 1.6 oz.  If ALL of that were suspended (as opposed to being at the bottom of the carboy in the yeast cake), then that would increase the SG by 13 points.  Since 90% of the yeast is at the bottom of the carboy (not suspended), the SG impact is ~1/10th or 1.5 points.  That's one tick mark on your hydrometer, or about the deviation due to the meniscus.
R.I.P.:Belgian Blonde
On Tap: Apfelwein, Kolsch(v2), Pumpkin Ale, Belgian Specialty 
Aging/Storing: Coffee Porter, Chocolate Porter, Flanders Red, English Barlywine
Fermenting: Maggie's Altbier
Next Up: PtE(1.1), Belgian Dubbel?

Working thru all BCS recipes