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Jun 08, 2022 View:

Laboratory still for proof obscuration

Howdy folks,

We are working on a product that will likely have quite a bit more than 600mg of solids per 100mL volume. I'm aware that this will make proofing pretty difficult by distillation. I'm wondering what others are using to determine proof in liquids with lots of dissolved solids?

I'm aware that there are some approved procedures mentioned in the CFR, however does anyone have thoughts on the definition of a "laboratory still"?

We have a small rotary evaporator that could increase surface area and make distilling alcohol out of this sludge a bit easier. However, since it's not a closed-system (because it has a vacuum pump pulling ), I'm unsure if a unit like this fits the requirements of the CFR.

Anyone using a rota-vap out there? Thoughts for us?


When this is the case, generally people will dilute the product to make it easier to distill. The important part is to keep track of your beginning mass and added water mass. If you normally use, say, 500 ml in your bench still, use a volumetric flask to instead use 250 ml product and 250 ml pure water. If your volume collected at 212 is less than 250 ml, simply add water to get 250 and you're good. If your collected distillate is over 250, then you'll have to add water to make up 500 ml and get down and dirty with your mathiness.

I don't see any problem using a roto-vap. There's nothing that prohibits using a vacuum to get your sample for determining your obscuration. Just ensure that the vacuum is being properly pulled at the receiver, and that the cooling is sufficient that you aren't dealing with losses from vapor at the vacuum attachment.

sounds like fun :-)

Reply: has nice (and cheap) obscuration stills.