Hi there, we have been having issues with testing the ABV of our gin, we have a few gins that use flavourings, some of these flavourings do have sugar in them. We have 2 different testing machines and they are both coming up with different numbers, we need the percentage to be pretty exact. Does the sugar in the alcohol affect the ABV readings?
Reply:49 minutes ago, Dylan.Daigle said:
For spirits containing alcohol and water only, you can determine the alcohol content by measuring either the density or the refractive index of the spirit. Adding sugar will impact on these readings and you cannot use the standard tables. The sugar changes the density in the opposite direction to the alcohol, but it moves the refractive index in the same direction as the alcohol. These 2 opposing effects can be combined mathematically to determine the abv and the sugar content at the same time. There are machines from Anton Paar and Rudolph Research that do this, but they are not accepted by the TTB. Only the lab distillation described by JailBreak is accepted.
What 2 machines are you using currently?
We currently use Anton paar machines, one is the Alex 500 model and the other is the handheld Snap 41, they both have different ranges and sensitivties, they also both have their limitations, the handheld doesnt do well with testing darker spirits like whiskey, and the alex 500 cant test anything over 50% abv
The Snap 41 measures SG only and will be confused by the sugar. Ignore the results you get from this unit.
The Alex 500 is designed to measure solids as well as alcohol but the web page does not say how it does it. The fact that it does not work well for high (> 50 abv) alcohol levels suggests that it is using Refractive Index as its second measurement because I know that the mathematics for combining SG and RI does not work well for high abv. You should give Anton Paar a call and ask them if the Alex 500 is suitable for your application - I believe that it is.
Below are some extracts from TTB requirements.
I make a coffee liqueur which has very much in excess of 600 mg of solids per 100 mL
I distill off 250 mL in a glass lab still, if I boil off any more than about 70% of the original volume I find that my condensate goes cloudy and the apparent ABV readings start dropping. I assume that solids are being evaporated as the boiling point increases, and are condensed into my collection flask so re-obscuring the true ABV.
My understanding is 30.32 (c) says the sample must be distilled until there is only 1 or 2 mL left in the flask, but it does not mention the size of the sample. If the original sample was 250 mL<which is quite common, that 1 mL would be charcoal.
§ 30.32 Determination of proof obscuration.
(a) General. Proof obscuration of spirits containing more than 400 but not more than 600 milligrams of solids per 100 milliliters shall be determined by one of the following methods.
(b) Evaporation method. ........................
(c) Distillation method. Determine the apparent proof and temperature of the sample of spirits and then distill a carefully measured sample in a small laboratory still, and collect a quantity of the distillate, 1 or 2 milliliters less than the original sample. The distillate is adjusted to the original temperature and restored to the original volume by addition of distilled water. The proof of the restored distillate is then determined by use of a precision hydrometer and thermometer in accordance with the provisions of §13.23 to the nearest 0.1 degree of proof. ................
§ 30.31 Determination of proof.
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(a) General. The proof of spirits shall be determined to the nearest tenth degree which shall be the proof used in determining the proof gallons.
(b) Solids content not more than 600 milligrams. Except as otherwise authorized by the appropriate TTB officer, the proof of spirits containing not more than 600 milligrams of solids per 100 milliliters of spirits shall be determined by the use of a hydrometer and thermometer in accordance with the provisions of §30.23 except that if such spirits contain solids in excess of 400 milligrams but not in excess of 600 milligrams per 100 milliliters at gauge proof, there shall be added to the proof so determined the obscuration determined as prescribed in §30.32.
(c) Solids content over 600 milligrams. If such spirits contain solids in excess of 600 milligrams per 100 milliliters at gauge proof, the proof shall be determined on the basis of true proof determined as follows:
(1) By the use of a hydrometer and a thermometer after the spirits have been distilled in a small laboratory still and restored to the original volume and temperature by the addition of pure water to the distillate; or
(2) By a recognized laboratory method which is equal or superior in accuracy to the distillation method.
Thanks for the help everyone, really appreciate it. Our solution we came to was to use the Alex 500 for our gin but we run a sample through some paper filters that came with the machine, i think it said 4 micron and it gave us readings .4 below our previous readings, seems to be an efficient way so far
Very biased opinion here; I've been really impressed with the Alex 500 for spirits. It was originally designed for beer and wine but recently upgraded to also measure spirits. There will be obscuration for heavily flavored spirits, but measurements are typically very repeatable. Some samples may need filtration beforehand for any undissolved solids. You can go here for a quote: https://www.anton-paar.com/us-en/products/details/alcohol-and-extract-meter-alex-500/ Your local rep will follow up and they can arrange for you to see it.
Reply:On 2/20/2021 at 6:45 PM, PeteB said:
I do add extra water the flask after the 250 mL but maybe not as much as you have suggested. I will try with more water and see what happens.
My condenser does not usually become contaminated as long as I switch off heat soon after that cloudy distillate stage.
One time I measured the ABV of a cloudy sample of distillate, then re-distilled it and the distillate was clear and the apparent ABV increased.
@PeteB Here is a similar discussion we had a few years ago and how a customer of mine solved the same issue. Even the commercial lab could not get consistent, accurate results
9 hours ago, PeteB said:
I have an Anton-Parr Snap 41. I tested the ABV of a diluted 3 year barrel aged whisky and it reads right on 44% as expected. Extracts dissolved from the barrel could possibly cause obscuration but I would not have expected much in 3 years. I would also expect any dissolved substances to increase the density of the whisky which would cause the Anton to give a lower reading than the true reading. I sent a sample off to be tested by distillation method at a certified Lab and their result was 43.1%. As mentioned I would have expected the lab reading to be higher. I did a re-calibration of the Anton and still got same answer and also measured several commercial whiskies and got the expected readings. Any ideas about the unexpected readings?
I have found the answer to the unexpected results, the lab stuffed up. I sent another sample of the same batch without telling them it was the same and the result came back at 44.7%, I think that is also wrong.
the first test report was 43.1% that's a 1.6% variation.
We have labelled and packed up a pallet for an international order with the wrong ABV.
We will have to re-label the bottles when we find the correct ABV. A lot of time and expense to fix and I won't be paying for it.
Hello Pete. A good cross check on these numbers is to measure the solids content by evaporation. This is an easy test that can be done using fairly basic equipment. The 44 % ABV that you measured with the Snap 41 is the apparent ABV. As you said, the true ABV would be expected to be higher than this because the dissolved solids would increase the density of the spirits.
It looks like the initial lab result of 43.1 % ABV was definitely wrong because it should not have been less than the 44 you measured. Whatever the solids are that have been dissolved out of wood, their density should not be too far from that of sucrose. Wood is made up of cellulose and hemi-cellulose which are just polymerised sugars. It would take very little dissolved sugar to change the measured ABV by the small difference you are seeing between the lab result and the apparent ABV.
To cause a spirit with a true ABV of 44.7 % to give an apparent ABV of 44 % would require only 3.4 gram/litre (or 0.36 Brix) of dissolved sugar. Measuring the actual dissolved solids will give a good indication of the expected obscuration.