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JoshR

Hydrometers and Specific Gravity 101

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Question: After I take the initial specific gravity of the wort, can I use the same sample for future measurements, or must I draw a new sample each time?

 

No.  You drank it, how can you use it again?   ;)

 

Often debated, here's some reasons why you should NOT:

 

- not same temp as beer due to location plus doesn't get the heat off the LBK full of fermenting liquid

- may become contaminated resulting in a different gravity reading

- may have more, or less, yeast cells than the wort so you get a higher or lower reading

- may evaporate differently than the LBK, so it becomes more concentrated, leading to a higher reading

- may get tipped over and break your hydrometer, because they do commit suicide

- you drank it (yes, repeated)

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I tried that I think it was in part that my testing area I had the tube on wasn't level so I had to very carefully adjust the tube till the hydrometer was floating straight in the tube. Just wondering if the sticking was a common problem and share my experience.

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My hydrometer, God rest its soul, committed suicide on 2/26/15 after giving me an OG of 1.058 on my second batch of CAL with additional malts and hops.  Jumped right off the damn kitchen counter, it did.  Replacement procured; considering obtaining a back-up since they appear to be squirrely. 

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My hydrometer, God rest its soul, committed suicide on 2/26/15 after giving me an OG of 1.058 on my second batch of CAL with additional malts and hops.  Jumped right off the damn kitchen counter, it did.  Replacement procured; considering obtaining a back-up since they appear to be squirrely. 

buy 'em in pairs, they seem to get depressed when alone

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Most hydrometers are calibrated to give correct readings at 59-60 degrees Fahrenheit. Higher temperatures thin the liquid slightly and result in lower readings than you'd get at the correct temperature. At 70 degrees F., the reading will be 0.001 low. To correct it, add 0.001 to the reading. At 77 degrees F., add 0.002. At 84 degrees F., add 0.003. At 95 degrees F., add 0.005. At temperatures above 95 degrees F., you risk killing your yeast and losing your beer. If you can't remember all that just print out the chart below.

hydrometer_correction_chart.jpg

Another thing you need to know is that most hydrometers come with three scales. Specific Gravity, Balling, and Brix are the ones that are usually on your hydrometer. Specific Gravity and Brix are the ones that are most used. Sugar can be measured as ounces per gallon, or as degrees Balling, or Brix. Ounces per gallon are measured on a numeric scale in which an S.G. of 1.046 equals 16 oz. (one pound) of sugar per U.S. gallon. Brix is measured as a percentage of sugar by which pure water has a Brix of 0 (or 0% sugar), an S.G. of 1.046 equals a Brix of 11.5 (11.5% sugar), and an S.G. of 1.095 equals a Brix of 22.5 (22.5% sugar). If you have a choice and want to simplify your life, buy a hydrometer that measures sugar by ounces per gallon.

That should cover everything you need to know about your hydrometer and how to use it. Here are a few tools that may help:

Handy Tools:

Brix/SG Conversion Calculator

Hydrometer Temperature Adjustment Calculator

Cheers!

 

 

 

 

When you speak of the temperature the hydrometer is calibrated, that would be the temperature of the wort and not room temperature?

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Yes, wort. Normally the adjustment is .001 or less, so a reading of 1.06 becomes 1.061. Usually makes little diff. And if you pitch at 64 and are done at 64, adjustments negate each other.  In other words, you are adjusting OG and FG for temps different than the hydrometer is calibrated at.  Then you take OG, subtract FG, and multiple the result by 131.25.  Therefore, if both OG and FG were taken at the same temperatures, regardless of how you adjust them the difference is the same as if you hadn't adjusted them.

 

In reality, it really doesn't matter a hoot for most of us.

 

Example:

 

OG of 1.060, temp of 70.  FG of 1.008, temp of 64.

 

ABV UNADJUSTED is 1.060 - 1.008 x 131.25 = 6.825%.

 

ABV ADJUSTED = (1.060 + .001) - (1.008 - 0) x 131.25 = 6.956%.

 

Does it really matter if you're 6.8% ABV or 7%?  And did you then adjust for the sugar when you carbonate?  

 

When it matters is if you start with wort or end with wort that is very different in temperature.  

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