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Jun 08, 2022 View:

Proofing and then resting

Have you all noticed that when you proof your spirits there is a time needed to reach a final equilibrium? In my limited experience I found that the proof takes some time to reach its ultimate specific gravity. Using a hydrometer it seemed to me that my proof read differently right after blending compared to a reading made the next day. The proof would go down as compared to my initial read.

I only have experience blending batches of a few gallons and not 100 or more like a lot of you.

I am pretty sure I have read about this before, and it isn't a fabrication of my imagination.

With that in mind, do you all have a minimum time you rest your proofed spirits before bottling?

I'm not sure it matters assuming you know you will nail the proof you want, but I would imagine the volume changes a bit too and you need to get that right in the bottle also.

Thank you,

Mars


Reply:

If you don't have it yet, check out a great little ap called the Distiller's Toolbox (I think it was free). They have a proof calculator that has been very accurate for me. Dial it in, dilute and then mix well.


Reply:

If you don't have it yet, check out a great little ap called the Distiller's Toolbox (I think it was free). They have a proof calculator that has been very accurate for me. Dial it in, dilute and then mix well.


Reply:

Mars, how much mixing are you doing when you blend? I've noticed variances from the expected proof, but after we started doing more extensive mixing we're a lot more accurate. We circulate the spirits for 5-10 minutes using a diaphragm pump.


Reply:

There are two factors which cause freshly blended spirits to appear to be at a higher proof than expected. The first is the heat of mixing. As the spirit mixes and warms up the density decreases and this looks like an increase in proof. You can correct for this by accurately measuring the temperature of the blend - if you have mixed sufficiently for the whole batch to be at a uniform temperature - and then correcting your hydrometer reading to the standard temperature.

The second effect can only be overcome by allowing the blend to "rest". Depending on how you blend, you will entrain an amount of air into the blend. The large bubbles, which you can easily see with the naked eye, rise to the surface in a few seconds. However there are also micro-bubbles formed which are so small that the small bouyancy force is counteracted by the viscosity and surface tension of the blend, and these bubbles rise very slowly. You cannot see these bubbles with the naked eye. But their presence lowers the density of the spirit slightly, giving the impression of the proof being high. As you have observed, leaving the blend to rest overnight allows the bubbles to escape and the correct proof to be read the next day.


Reply:

When diluting ('proofing' in the US) a spirit above 80%, with water, you get an exothermic reaction which causes the mixture to heat up, you often (depending on dilution water quality and pre-treatment) see the mixture cloud over as dissolved oxygen in the water is liberated. The temp increase will through your hydro temp calibration off, so temp correct, the gas bubble will reduce the density of the liquid as well.

We always mix well, and stand for 2-3 hours before taking final readings.


Reply:

Thanks for all the responses. I will definitely make mixing and some resting as part of my procedure.

As far as the hard to determine micro scale physio-chemistry goes, I want to also share another observation. I recently roughly proofed a few bottles from barrel strength to 40%. I blended the spirit and water in each bottle and did end up hitting my target pretty well. What I noticed though, is that the day after proofing, if I upended a bottle I could see mixing of the liquid inside indicating different refractive index for different liquid sitting in different parts of the bottle. That wouldn't be likely to happen if I had mixed well ahead of time, but I think it is evidence that there may be effects beyond the temperature and bubbles.

I am not sure that this is of any practical importance for now, and it may be pedantic, but I like getting into these things because it will help someone someday.

Thanks for answering my real question of how to blend properly.