Bringing balance to the foreshots

A joint essay & publication by Matthew Fergusson-Stewart of Whisky Molecules, and Whisky & Wisdom.

A long time ago, in a galaxy far, far away, your two correspondents were co-hosting a tasting event together and explaining the distillation process to the audience, going into detail about the fractioning – better known as the foreshots, middle cut, and feints.  We explained that the foreshots was heavy in methanols and other undesirable elements, which everyone was happy to accept.  We also explained how the foreshots and feints are never wasted, but are mixed back in with the next batch of low wines, and the process continues repeatedly. Everyone was happy to accept that, too.  Well, almost everyone.  One chap sitting near the front objected: “If the foreshots keep being recycled and mixed back in, won’t you get a continually increasing build-up of methanol in the spirit?”   Ummmm……

It’s a vexing question that’s since been posed to us both many times.  What do they do with the methanol and where does it go?

Let’s back up a step:  Most whisky enthusiasts know that distilleries cut (remove) the foreshots as the spirit flows from the spirit still, along with the feints.  The methanol which is formed during fermentation becomes concentrated to toxic levels during distillation and needs to be removed.  Methanol has a lower boiling point than ethanol, and so it is amongst the first compounds to make it up over the lyne arm in the form of steam as the liquid in the still starts to boil.

Some whisky enthusiasts also know that the foreshots and feints that we cut during distillation are not simply tipped down the drain; they are transferred to and stored in the feints receiver, where they are later combined with the low wines of the subsequent batch for the next round of distillation through the spirit still.  Pot stills are actually very inefficient at separating different liquids, so it’s worth recycling through to get more of the good stuff that gets left behind in both the foreshots and the feints with each run.

The dilemma for us was clear:  Small volumes of methanol are created with every new batch, and that methanol is also cut from every single batch in the foreshots and retained in the system, so we must be gradually building up methanol over time.  What were the possible outcomes, we pondered?  The methanol either:

• Builds up in volume. (But then what?)
• Is periodically removed from the system.
• Leaks out through evaporation.
• Is chemically consumed.

Let’s explore each of these four possibilities…

Could it be building up in volume?  There are distilleries producing millions of litres of spirit per year, and there are distilleries that have been operating for, literally, hundreds of years. If it simply built up in volume indefinitely, enormous feints receivers would be as common on the Speyside landscape as re-purposed pagoda rooftops.  So let’s quash that possibility.  Moving on…

A former distillery manager we’re both well acquainted with, when asked this question, was very clear: It was not periodically removed from the system at the distilleries he has managed. It may well be disposed of in an environmentally-appropriate manner at some smaller distilleries, particularly those that regularly switch spirit styles (such as between peated and non-peated campaigns) and thus where they do not want the flavour of one style contaminating the other.  Larger distilleries, however, often have a separate feints receiver to help manage these changing flavour profiles.  Strike two.

Leakage? Methanol is highly volatile, that’s why it comes through early during distillation and can be removed in the foreshots. It also means that, inevitably, some of it may leak out of the system through evaporation, particularly as it flows through spirit safes and sits in feints receivers that may not be particularly well sealed. However, despite our romantic notions of clearic flowing through beautiful brass and glass boxes, and of studious workmen turning the handle at just the right moment, most large distilleries – particularly workhorse distilleries – actually have their spirit flowing through sealed pipes with ‘the cut’ made by hidden sensors and solenoids. If methanol was leaking out as quickly as it was created, it would also become hazardous to health, as it is deadly by inhalation as well as ingestion, and therefore absolutely unacceptable in the modern era of workplace health and safety regulations.  It is also classified as ‘F – Highly Flammable’ under the European DSD classification.  Strike three.

This leaves us with the methanol not being removed, but being changed into something else through chemical processes.  Putting our heads together, we identified two possible pathways by which this may occur:

1. Atmospheric methanol breaks down to CO2 and H2O (carbon dioxide and water) in just a few days, but we had no idea whether conditions for this were right in the feints receiver/spirit distillation cycle?

2. The feints receiver could be a source of esterification, as esters are made by combining alcohols and acids. Methanol is, of course, the shortest chain alcohol, and the feints receiver is a highly acidic environment. But again, we had no idea if this was what actually goes on in the feints receiver?

So we decided to ask some experts: Brian Kinsman, Malt Master at Glenfiddich; David Baker, distiller at Australian distillery Bakery Hill; and Dr Bill Lumsden, former manager at Glenmorangie and these days Director of Distilling and Whisky Creation across the Glenmorangie/Ardbeg brands.

The answer?  It transpired that none of our ideas were correct!  There is no build up of methanol; it is not removed from the system through either leakage or deliberate action; and it is not (significantly) chemically consumed by reactions in the feints receiver or the still.  So what does happen to it?

Reality and science offered a far simpler explanation:  The answer is nothing.  Nothing happens to it, because it does not build up in the system.  Methanol, in the system, is in a perpetual state of balance.

What???  Let’s go back to the beginning…

Methanol is physically produced during fermentation and it is approximately 2-3 parts per million (ppm) in the wash (or beer, if you prefer). This is a safe level, and should be fairly consistent with any strong beer, which is exactly what wash is.  (If you’re curious, methanol results primarily from the degradation of ‘pectins’, or arabino-xylan compounds (pentosans) which are found in cell walls.  Generally speaking, the resulting starch substrate from a cereal mash does not degrade as readily to produce the precursors for methanol production – at least not nearly as much as occurs with the fermentation of, say, a mash made from stone fruits.  The tiny amount of cell wall degradation which can occur in cereals results in pentose sugars (5-carbon rather than 6-carbon ring structures), which are not able to be fermented by standard brewing/distilling yeast).

In any event, the methanol concentration of 2-3ppm in the wash is then further concentrated during the first distillation and increases to approximately 6ppm in the low wines. The concentration has increased because we have removed a lot of pot ale, which does not contain any methanol. The level in the low wines is still perfectly safe for consumption.  In order to cause permanent blindness, the average human must consume 10mL of methanol. At 6ppm, this would mean you need to consume 1.66 million mL (1,660 litres) of low wines in order to cause blindness. You’d die from a ruptured stomach long before the methanol got to you!

After the methanol has been concentrated to 6ppm in the first distillation, we move on to the second distillation. Methanol is quite volatile, with a boiling point of approximately 65 degrees Celsius (ethanol is 72 degrees, water is 100 degrees) and thus it tends to be highly concentrated towards the foreshots end of the spirit run, where it is typically now around 20-40ppm.   At this concentration (remember, this is in the foreshots now), we are now looking at levels that may not push towards that which would cause death or blindness were they to be included in the final spirit, but we are looking at levels that could give you a nasty headache and exceed the safe “reference dose”.  Regardless, the foreshots contains more undesirables than merely the methanol, and since the spirit simply doesn’t “taste right”, it is despatched to the feints receiver.

Now here’s the crux of it – the foreshots cut does not remove all of the methanol. It is more concentrated in the foreshots at 20-40ppm, but it is still present at a lower (and completely safe) level of around 6ppm in the middle cut. (Both Kinsman & Lumsden confirmed that the concentration of methanol in the new make spirit for Glenfiddich and Glenmorangie respectively was around 6ppm).  That 6ppm should sound familiar, because that was the level in the low wines!

In other words, the new methanol that we are creating and introducing to the system with each fermentation is essentially the same amount of methanol that is leaving the system with each cut of new make spirit.  The following graphic illustrates the situation:

 

The foreshots’ methanol concentration is much higher (and unsafe), but once it’s transferred to the receiver, it is diluted by the feints, which have negligible methanol content.  Both the new make spirit and the liquid that remains in the system are running at a constant 6ppm methanol, never significantly increasing or decreasing.  Pot still distillation eventually brings about an equilibrium level in the receiver that – once reached – will not change unless you change other aspects of your production such as wash percentage, low wines percentage or cut points.

You should also keep in mind that at most distilleries, the new make spirit is then diluted to 63.5% ABV before it goes into casks, which along with the ethanol, reduces the concentration of the methanol by about 10%. Once in the cask, the Angels’ Share comes into play, and the forces that act upon ethanol in this phenomenon will act even more assertively upon methanol, so the concentration of methanol in the cask will continue to decline with age.

If you’re still confused, just think of the methanol produced during fermentation as being a Dark Lord of the Sith, and the feints receiver as being the Jedi.  It restores balance to the force.

Jedi Master Level addendum

Now some of you are already getting ready to hit the Comments button with a rant about how different distilleries cut at different times and strengths, so the new make spirit can’t always be the same as the low wines going into the system.  We find your lack of faith disturbing.  Let’s imagine a distillery that does a late cut.  They will be taking less methanol out of the system in the middle cut and also taking out a little bit more of the feints that would otherwise help dilute the foreshots. With more foreshots and less feints in the feints receiver, that should mean that methanol will start to build up in the system. Well, it does, but only for a little while.  As there is now a slightly higher concentration of methanol in the system, our inefficient friend, the pot still, will not be able to remove it all during the run of foreshots and it will start to push through into the middle cut until the system reaches a new equilibrium. The opposite applies at a distillery that takes an early cut.

Cheers,

Matthew – https://www.facebook.com/WhiskyMolecules

Andrew – www.whiskyandwisdom.com