Internal reflux?

[Watershed]

Doing my birch vodka I hit a curious snag - I was running the still as slow as I could get it to go, the input was a 60% ( one distilation ) wash. Output under 1l per hour. 5l in the pot. It started coming out at 87% and at 82% I'd collected just over a litre.
At that point the output stopped. Checked the heat - still there and I could hear the wash simmering so fearing the worst I shut down on the assumption that it had clogged.

No trace of a blockage.

All I can think is that running it that slow, once the ABV in the still hit a certain point natural heat loss to the air was enough to cause condensation on the lid of the still with none making it to the coils - 100% reflux.

Any other possibilities and if not - how can I best exploit this?

[furball]

With out being there, it is hard to say. But on the assumption you have that there is enough external cooling to knock down your vapor, try insulating the body and the column, especially the column.

Furball

[possum]

I've had similar trouble when stillin on a water bath. Insulation could do the trick. I've used old ratty towles to wrap around my boiler, especially at the cap/top of boiler. I bet that most of the ethanol was gone at that point. 5lbs of sugar wont make much more than a liter of 80%abv. Did the stuff in the boiler taste like alcohol ? There could have been a leak that let the good alcohol vapor escape.

That is all I could come up with.

very interesting vodka watershead.

[Watershed]

My mistake - kilos not pounds! - wash of approx 14%.

No leak - I'd have smelt it. The simple answer is don't run it that slow again, I can't lag as I use a gas flame to heat ( well I could but it's not practical ). The question was more down to curiosity than anything else.

Even with all the alcohol off though I'd have expected water to come through.

[knuklehead]

During a run the output will always slow near the end. If you start off to slow it will slow down to nothing. I think your on the right track Watershed. Running it that slow you will have been getting uncontrolled internal reflux and near the end you where just at 100% reflux. My collections when running my pot still usually drop about 10 ml/minute form start to finish of a run so if I started collecting at 10 ml/min I would end up in the same situation.

[aldehyde]

I have definitely seen this happen in the lab. If you have a good enough separation you will see distillation slow, stop and then the temperature quickly increase to the next boiling point. Now, since this is an alcohol water mixture it obviously isn't as clear as that, I would guess that the % of alcohol in the vapor had decreased to a point where the vapor could recondense when it had moved far enough away from the heat source. Do you have a bend right before your condensor?

[Watershed]

I've got a right angle one inch above the top of the still then a 40cm lyne angled about 10degrees down off horizontal which smoothly joins the coil ( they're the same piece of copper )