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Specific Gravity Hydrometers


adamOVD

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I'm shopping for Proofing hydrometers, and I understand the need for accuracy in proofing hydrometers, especially before bottling. However, I fail to see the need for a super accurate set of 5, at 180$ each, of specific gravity hydrometers. Are they purely used for taking Starting and finishing gravities of the wash? Is there a greater purpose for them I am completely ignorant of? I've searched the proofing manual and videos, and can't find anything.

I'm coming from the beer industry, and as far as I know, there was no regulation put on hydrometers, and I'm baffled. Please someone set me straight.

Edited by adamOVD
Tried to clarify the question
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You need a full set to test the strength of your spirits off the still, at barreling strength, and bottling strength. If you produce liqueurs or lower strength spirits you probably need 0-20, 20-40, 40-60 etc. Accurately measuring and recording the proof is important to the government, as the tolerances for error are 10x smaller in spirits than beer, and the tax rate per unit of alcohol is probably 15x higher for spirits. 

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There are very specific requirements for accuracy. You must be +0 and -0.3 degrees of proof, and to do that, you need an accuracy of the hydrometer order of 0.1 or better, TTB often recommends another order of magnitude. Unless you get a very expensive digital hydrometer or densitometer, the cheapest way to measure proof to the required degree of accuracy are the calibrated narrow range glass hydrometers. You can self calibrate to an intermediate standard, and save money. You can get glass hydrometers of sufficient accuracy but without calibration for $30-$50. But calibration runs around $100, more or less. Don't forget, you also need a very accurate thermometer to be able to control or compensate for temperature, at least 0.1 deg C.

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@bluestar thanks for the reply. I may be misunderstanding you, but it seems to me you are still talking about proof hydrometers. This is the part of the TTB CFRs i"m trying to grasp.

§30.24   Specific gravity hydrometers.

(a) The specific gravity hydrometers furnished by proprietors to appropriate TTB officers shall conform to the standard specifications of the American Society for Testing and Materials (ASTM) for such instruments. Such specific gravity hydrometers shall be of a precision grade, standardization temperature 60 °/60 °F., and provided in the following ranges and subdivisions:

Range Subdivision
1.0000 to 1.0500 0.0005
1.0500 to 1.1000 0.0005
1.1000 to 1.1500 0.0005
1.1500 to 1.2000 0.0005
1.2000 to 1.2500 0.0005

No instrument shall be in error by more than 0.0005 specific gravity.

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12 hours ago, adamOVD said:

@bluestar thanks for the reply. I may be misunderstanding you, but it seems to me you are still talking about proof hydrometers. This is the part of the TTB CFRs i"m trying to grasp.

§30.24   Specific gravity hydrometers.

(a) The specific gravity hydrometers furnished by proprietors to appropriate TTB officers shall conform to the standard specifications of the American Society for Testing and Materials (ASTM) for such instruments. Such specific gravity hydrometers shall be of a precision grade, standardization temperature 60 °/60 °F., and provided in the following ranges and subdivisions:

Range Subdivision
1.0000 to 1.0500 0.0005
1.0500 to 1.1000 0.0005
1.1000 to 1.1500 0.0005
1.1500 to 1.2000 0.0005
1.2000 to 1.2500 0.0005

No instrument shall be in error by more than 0.0005 specific gravity.

I don't understand either.

The rage in the above table is not for pure alcohol + water solutions. They all have SG of less than 1

So what could TTB require you to read with such accuracy?

Original and final gravities come into this range but it is pointless measuring them to this accuracy because the theoretical alcohol yield is not nearly the same order of accuracy<_<

Liqueurs could be in this range but the SG is not going to tell much about the alcohol content

 

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Thanks for the replys. Seems these-

https://www.coleparmer.com/i/mn/0829780#eb-item-specification

say they conform to ASTM standard without the calibration service, so I'm going to order the 1.00-1.05 and 1.05-1.10 ranges and hope they're OK. Could some one describe how to calibrate an uncalibrated proofing hydrometer? Do I need one calibrated hydrometer from each range, or can I buy one one certified hydrometer in my lowest range, and one in the highest range, and then use that as a reference point to adjust my sample for the other ranges? Sorry for my ignorance.

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Calibration is typically either single-point or two-point.

For single  point, you use a calibrated hydrometer to read the proof and then compare that reading to the one given by the hydrometer to be calibrated. If the hydrometer you're calibrating is over or under, you record that and add/subtract that in the future to get a true reading. This is done at controlled temperatures - usually 60F - and typically aimed at the middle of the hydrometer's range.

For two-point, you make readings at either end of the range instead of the middle.

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Thanks @RobertS . So I do need a hydrometer in that range to certify another hydrometer. From what I've been reading on the forums and the CFRs, it seems like the TTB does not require you to have certified proofing hydrometers, but it is nearly impossible to be 100% certain you are within their tolerances (.3 proof) unless you have certified them. Does that sound about right?

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You are absolutely required to use a calibrated hydrometer for bottling, and I believe barrel transfers or any time product is leaving your bond.

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I believe I found the answer to my original question. You would need a well calibrated  specific gravity hydrometers to gauge spirits by weight, if over 600mg of solids.

"However, in the case of spirits which contain solids in excess of 600 milligrams per 100 milliliters, the quantity in proof gallons shall be determined by first ascertaining the wine gallons per pound of the spirits and multiplying the wine gallons per pound by the weight, in pounds, of the spirits being gauged and by the true proof (determined as prescribed in §30.31) and dividing the result by 100. The wine gallons per pound of spirits containing solids in excess of 600 milligrams per 100 milliliters shall be ascertained by:

(a) Use of a precision hydrometer and thermometer, in accordance with the provisions of §30.23, to determine the apparent proof of the spirits (if specific gravity at the temperature of the spirits is not more than 1.0) and reference to Table 4 for the wine gallons per pound, or

(b) Use of a specific gravity hydrometer, in accordance with the provisions of §30.25, to determine the specific gravity of the spirits (if the specific gravity at the temperature of the spirits is more than 1.0) and dividing that specific gravity (corrected to 60 degrees Fahrenheit) into the factor 0.120074 (the wine gallons per pound for water at 60 degrees Fahrenheit). When withdrawing a portion of the contents of a weighing tank, the difference between the quantity (ascertained by proofing and weighing) in the tank immediately before the removal of the spirits and the quantity (ascertained by proofing and weighing) in the tank immediately after the removal of the spirits shall be the quantity considered to be withdrawn"

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Sorry, your question was very confusing. You were asking MUST you have or WHY would you have these hydrometers. Yes, you would only have these if you CHOOSE to use a process that requires "specific gravity" hydrometers to make the measurement. But, you are NOT required to use those to make proof measurements. All required proof measurements for a distillery COULD be made using hydrometers calibrated in PROOF and making necessary corrections. Yes, the method you outline using weight gauging is one example of where you would use specific gravity hydrometers, but you don't have to use that method. The reason for the accuracy and calibration, however, is the same as I gave for the proof hydrometers, in as much as the required accuracy when pushed through the required calculations to determine proof from a method using a specific gravity hydrometer are to assure the same accuracy required for proof obtained using a proof hydrometer.

Was your question academic, or where you trying to determine if you need to purchase those specific gravity hydrometers?

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@bluestar sorry the question was confusing, should've simplified it. I tried to edit it a bit to clarify. What I really want to know, is

1) do I need to purchase precision specific gravity hydrometers. Cfrs say

"(a) The specific gravity hydrometers furnished by proprietors to appropriate TTB officers shall conform to the standard specifications of the American Society for Testing and Materials (ASTM) for such instruments. Such specific gravity hydrometers shall be of a precision grade, standardization temperature 60 °/60 °F., and provided in the following ranges and subdivisions" 

2) If yes, do they need to be calibrated? Again CFRS

"(b) A certificate of accuracy prepared by the instrument manufacturer for the instrument shall be furnished to the appropriate TTB officer."

3) Is there a purpose for such precise deliniation I am missing. (Found the one in my previous comment, but there may be more.)

Thanks.

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