A KEY DIFFERENCE BETWEEN BATCH DISTILLATION AND CONTINUOUS DISTILLATION?

A KEY DIFFERENCE BETWEEN BATCH DISTILLATION AND CONTINUOUS DISTILLATION?

From comments and responses on forums, I get the impression that even experienced home distillers don't really understand the difference between batch distillation and continuous distillation... They think that continuous distillation is just a kind of "automated batch distillation" where you feed "micro batches" to the boiler... But this isn't the case at all.

In a batch (pot or reflux) still the boiler keeps all compounds at the full boiling point of the wash all the time. The longer you heat the compounds in a wash, the more they will transform. Some undetected compounds will become nice flavors, while some will become horrible. Some will have an affinity for water, some will have an affinity for ethanol.

If you make non-neutral spirits, you want the desirable compounds, careful recipe selection and good fermentation are the most important factors in controlling what compounds form during the boil, as making cuts can only go so far in selecting the desirable compounds.

If you make neutral you don't want any compounds. In a batch still, there's only one way to eliminate flavors, and that is to have a higher purity going in and out. With the best yeast make a good, clean and well cleared wash. The fewer compounds present going in, the fewer can transform during the boil. Distill to high purity, make good cuts, double or even triple distill. So you end up with 95% ethanol with impurities, 1% water with impurities from the first distillation, and 4% clean water from the second and third distillations. Once formed, there is nothing you can do to eliminate the impurities that have an affinity for ethanol.

In continuous distillation, the compounds in the boiler do not rise above the lowest theoretical plate and the ethanol never falls below the lowest theoretical plate. i.e There is no ethanol in the boiler. There is no ethanol rising out of the boiler.

The temperature gradient created by the boiler at the bottom and the coolant at the top causes the ethanol to rise. As the preheated wash is injected in at the center of the still and begins to flow down the gradient, it reaches the point in the gradient where random micro boils vaporize the fractions and the vapor rises. When the vapor condenses slightly higher up, it mixes with the incoming wash again and dilutes the compounds that were evaporated at higher temperatures further down, causing the fresh wash to effectively flush compounds that have been boiling for a while, keeping them out of your distillate.

In micro continuous distillation, any fraction of the wash spends only a tiny amount of time at a given temperature before it moves down and out of harm's way. Think of it this way: In MyVodkaMaker the wash is pumped through at 7 ml per minute, and it has about 5 ml of wash exposed to the vapor/liquid refluxing process where compounds can form. So the wash residency is under a minute. Whether you do a 10-liter or a 200-liter run, the exposure time is the same...under a minute.

So why does wash residency or exposure matter? Consider a living yeast cell: It has a specific cell structure and cell integrity. Even when boiled at 90°C or higher, it takes some time for the cell to disintegrate and release its contents, which are then converted into yeast flavor... The yeast flavor will not be passed on to the distillate if the ethanol is removed and the cell is flushed down the drain before it breaks apart. The same can be said for any other compound.

When you make neutral with a micro continuous still (like MyVodkaMaker), you have control over purity, you have the flushing process, and reduced exposure. Purity is important... but in my opinion, the compounds that form during boiling have a greater impact on the taste. This opinion comes from the fact that I've personally distilled many, many bread yeast washes while they were still fermenting with active yeast in suspension at a gravity of 1020 and even at a modest 90% ABV I get a clean neutral with no yeast flavor. I just stick the feed tube in the barrel and run the still for a few hours and get enough for my need...the active ferment carries on undisturbed.



Conclusion If yeast cells can pass through your still before being broken up, you are preventing the formation of many other horrible compounds.... and you cannot carry over compounds that do not exist...this results in a very clean neutral.

Note: For brevity, I have described this in discrete and absolute language, but everything is a continuous gradient and smear, a little bit of everything goes everywhere, and compounds will transform even at room temperature.