Specific Gravity - Home Brew Forums

 Home Brew Forums > Specific Gravity

03-15-2006, 05:00 AM   #1
dougb
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Mar 2006
Posts: 7

I've just finished bottling my first home brew and things seem to have gone well. My pale ale has been in the bottles for about 10 days now, I tasted it tonight and was pleased.

The specific gravity was 1.050 just before I pitched the yeast and 1.013 when I bottled it. I have a lager that had a specific gravity of 1.048 prior to pitching the yeast and an IPA at 1.078 both activley fermenting as we speak. I didn't ask what I could expect the specific gravity to be before pitching or what it should be before bottling when I bought the supplies from a local brewery. How do I know what to expect as far as a beginning specific gravity and an ending specific gravity before bottling? Is there a general rule of thumb or formula that I can use to know how much lower the ending gravity should be from the beginning gravity before bottling? Thanks

03-15-2006, 08:09 AM   #2
flingdingo
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Mar 2006
LAX
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Your final gravity is dependent on how attenuative the yeast is. What type did you use? You can find out the attenuation at your store, or get pamphlets from the yeast manufacturers (farmers? herders? what do those guys call themselves?)

Then just do the math. If your brew started at 1.050, and your yeast has an attenuation of 70%, then

1. 100% - 70% = 30%

2. 50 x .30 = 15 or 1.015

You only need to worry about the numbers past the decimal because your beer will never ferment below 1.000.
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03-15-2006, 11:42 AM   #3
Brewsmith

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Some sugars are unfermentable. Grain mashed at higher temps will have more unfermentables than a wort from the same grain at lower temps. Being your first brew, I'm assuming you are using extracts, so this is not much of an issue. The attenuation math will get you close, but don't be suprised if it is a couple points either way.
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03-15-2006, 05:34 PM   #4
Blender

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Here is page for beer math. If you look at the bottom portion of the page there is a description on calculation OG in extract and speciality grains.
http://polymer.bu.edu/paul/homebrew/calculations.html
It may be useful.
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03-16-2006, 06:41 AM   #5
Lost
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If you're buying kits then they will often tell you what the expected Original Gravity will be. There is also not much room for variance since extract is extract.. there are no efficiency concerns or worries over incomplete starch conversion as there would be with all grain batches. The extract is just sugar.. as such the only way you can end up with a lower than expected OG would be if you didn't use all the extract, spilled it, had a boil over, or added too much top up water.

Generally speaking the final gravity of your beer will typically be somewhere in the 1.014 range though, as others have said, the sugar profile and yeast strain can have an affect on this. For example, large amounts of fermentable sugar (i.e. corn sugar) would result in a drier, more alcoholic, watery beer & a thus a lower FG.

03-16-2006, 02:53 PM   #6
Walker
I use secondaries. :p

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also.. you can plug the extract/sugar/grain part of your recipe into The Recipator's spreadsheet (http://hbd.org/recipator) to get an idea of what the starting gravity will be like. It's just a guide, and only a hydrometer can REALLY tell you what you have in the fermenter.

-wlker
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