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Novice Guide for Cuts (pot still) by kiwistiller » Wed Sep 16, 2009 4:17 pm
This guide is aimed at educating a pot still novice about the different fractions in a distillation, and to help them learn how to make cuts between them.
Cuts are the points in a distillation run where the stiller separates the distillate into separate fractions (divisions between sections of the run). In order to make good cuts, it is important to understand what the different fractions of a run are, and how to recognise them.
Once you know your equipment and your mash, fractions are fairly predictable. The ABV% will drop (and temp will rise) over the course of the run, and this is one indicator of cut points that can be used as a crutch to judge with. However, temperature and %ABV are not recommended as a guide for cuts. Vapour temp is directly related to %ABV, just basic physics. If you know the temp you can reliably predict the %abv, and vice versa. They tell you the same information. For example, 20% abv output = 98C. There is a chart for converting temps to %ABV and a more detailed discussion of this here
There is an issue of reading the temp correctly, ie in the right place, at the very top of the vapour path, just where it turns down into the lyne arm / product condenser. But that is a very minor design detail compared to the unreliability of thermometers.
Temp is no worse than %abv for deciding where to make the cuts, but both are rough guides at best. Cuts are (should be) ultimately made by taste and smell, not %abv or vapour temp.
I will provide some ROUGH figures as to where the fractions can be expected. These will be in %ABV as I think the average alcoholmeter / alcometer is probably more accurate than the average thermometer, and many folks don't have thermometers in their pot stills. Fractions normally follow this rough outline:
This fraction is the first part of the distillate collected. A major component of this fraction is acetone, or nail polish remover. But there are other compounds in there as well. In my experience, often the very first drops of foreshots, that can start slowly coming over from around 40-45C, have a wonderful, rich, sweet smell, but you really don't want to be drinking this stuff (headache city ).
On a pot still, the absolute minimum that should be allocated to foreshots is 150ml per 25l of wash. So, for a second distillation of, say, 3 stripped 25l washes (with no cuts made in the first distillation), you would want to discard 450ml of foreshots. This fraction should never be recycled, or used in any way for beverages, but it does have some uses. It's a great solvent, can be saved for cleaning runs of new stilling equipment, and is great for starting charcoal BBQs. Use it around the house / shed in place of methylated spirits (denatured alcohol).
In my still charged with 40% low wines, this fraction reads about 82% on the alcoholmeter / alcometer)
Heads are a mix of methanol, acetone, ethyl-acetate and ethanol as the main components.
Because a pot still does not separate the different fractions very cleanly, there will be diminishing 'nasty stuff' and increasing hearts (ethanol) throughout this fraction. While not completely awful like the foreshots, heads is generally blamed for hangovers, and a sharp biting taste. Like foreshots, they can smell sometimes smell a little sweet and buttery, but will have a biting, solvent like, alcohol sting to them as well. Many seasoned shiners will start to notice heads in store bought alcohol, especially vodkas. Most people find it desirable to remove the heads from finished product as well as the foreshots. There is however a lot of usable ethanol in the heads fraction, so the standard practice is to save the heads in a separate 'feints' (see later) container for further processing. If you can't be bothered, throw them in with the foreshots.
In my still charged with 40% low wines, this fraction is from about 82 to 80% on the alcoholmeter /alcometer. In our hypothetical still charge of three stripped 25l sugar washes, I would expect to collect roughly 2-3 liters of heads, maybe more (I really don't like them). Some people are more sensitive to the tastes of different fractions than others, so you will have to find your own tolerances. Also, some washes will produce a lot more heads / foreshots than others. Apple brandy, for example, is notorious for having a large proportion of heads, while for a full bodied, sweet rum, you might actually want a touch of heads in your final (at the cost of the headache that follows the next day, probably).
The hearts, or 'body' fraction as it is sometimes called is the purest section of the run in ethanol terms. Hearts is very clean tasting and smelling, without the chemical bite of heads, but still with good flavour. When you are blending your fractions, the hearts should be considered the foundation that you build your product on.
Hearts will generally start around 80% abv in a run of 40% low wines, but again, this will vary. A very conservative lower cut for, say, a mild whisky, might be 70%. for a full bodied spirit like rum, you may go quite deep into the tails, even as low as 50%. Some may go even lower. The hearts will probably be the biggest fraction you collect in your run, but this will again depend upon what you are making.
The tails of a run are signalled by the distinctive and pretty unpleasant smell of wet dog, wet cardboard, damp socks, etc. As well as the change in smell and tastes, and the dropping ABV, the collection rate for a given power input slows as well at the onset of tails, (and continues to fall through the tails).
Tails are rich in fusel oils, which cause unwanted tastes in your product. Some times you can see an oily film on top of the collected tails. Some parts of the tails, if left for a day or so, will start to develop floating crystalline... things. This is all highly undesirable in your product.
As the tails progress, the underlying taste of the product will probably become stronger, and more bitter, cardboardy notes will keep coming through. Late tails generally just tastes of dirty water to me. This will vary substantially depending upon the mash.
The tails still have quite a high proportion of ethanol, however, and some of the deepest flavours of all can be hidden in the tails fraction (see Pugirum for a discussion of this). It is generally desirable to recycle these tails with the heads into the feints container, and add them back to the next run. Alternatively, if storage is not an issue for you, you can save them up and do a all feints run, which will produce a very special, deeply flavourful product. This is highly recommended, for a rum at least. Other flavoured spirits may vary. There is no point doing this for a neutral/ vodka of course.
ASIDE: if you are running an all feints spirit charge, it might be better to do these runs a bit slower than usual for a spirit run.
Tails are normally collected until the distiller decides the abv returned is not worth the time and heat being applied to the still. Personally, I take down to 10%, but many people seem to use 20%.
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