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Jun 08, 2022 View:

Calculating Obscuration

Can someone just give me a run down on how to account for obscuration?

I get that you take an exact amount, Distill this collect the distillate adjust the temp so that its the same as when you started and add water to reach the exact amount you started with. Then take the true proof reading.

So for example you start with 1000 ml of 100 proof (before you distill it and ad water)

After you distill it and ad water I'm assuming your proof will go down. Is this correct?

Also assuming the obscuration number is the difference between your starting proof and your end proof?

Once you have this number can you just adjust your proof readings by this or do you have to re distill a small amount every time you step down getting closer to proof?


I have only done obscuration testing with a lab still for beer and ciders. Your method is the same as I use, assuming the water you added is also at the same temperature.

The "gunk" that is left behind in the boiler will generally have a higher density than the condensate which means the condensate will have a lower density than the original sample.

Lower density gives a higher proof reading so you will need to add more water (as well as the makeup water) if you want to get it back to 100 proof.

You should be able to calculate the amount of water to add and then one more lab distillation would be needed to satisfy TTB (and yourself) that you have got it right.