Originally By Tony Ackland
Running the StillFor neutral spirits. there are many different ways of running a still to achieving the same results.
To get high purity, you require your column to be doing many redistillations. To get enough redistillations happening, your packing must offer sufficient "theoretical plates". The HETP that you get from packing depends on many factors, but includes the surface area, the thickness of the liquid spread out over it, and the ratio of liquid to gas. As the alcohol in the pot depletes, in order to keep the same purity, you need more redistillations happening. The usual way to do this is to improve the HETP by increasing the ratio of liquid to vapour (eg the reflux ratio)
As its a ratio, you can do it either by increasing the amount of liquid being returned (eg increase the amount of cooling water to through tubes/top condensors, or closing the offtake in a Nixon-Stone ), or by reducing the amount of vapour (by reducing the power input to the boiler). Both will have the same result.
Just how much action is required depends on what the column is like to begin with. If its a tall column, packed with something with heaps of surface area (scrubbers), etc, it may already have enough redistillations happening in it to satisfactorily cope with very low alcohol input. Thus there would be no need to adjust it much during the course of the run. You'd basically turn it on, set it and leave it (though you still need to catch it right at the end).
If however the column isn't quite so great, you might need to do some serious readjusting of the reflux ratio right through the run in order to keep it doing what you desire.
Likewise, with the tall column, maybe you elect to run it heaps faster at the start (and not suffer any ill consequences), but then progressively turn it back down as things progress. Eg - do you run it the whole run at say 10 mL/min offtake, and never touch it, or say start at 50 mL/min and then slowly wind it back to 10 mL/min over the following hours.
None of these are wrong or right, just different. So when you hear of guys doing 17hr runs, thats fine if it suits them. I prefer the latter of fiddling to get the shortest time. Each to their own. With rushing, I have more "oops" happening - finding that I haven't been checking it quite routinely enough, and that its just spent the last 10-15min at too high a temp. But I'm still happy with the final taste, so thats fine for me. Others may shun my juice.
Choose for youself - try a run at a really slow offtake & little control needed, and compare against a "hands on, push it fast" approach. Maybe choose the middle ground.
Likewise as to go to electronic control or not - its just a personal choice, based on if the smoother control is worth the cost, if whether it will work for your style of operation & still design, if you dabble in that sort of thing, or if you prefer the hands on and driving.