Wednesday 22 March 2017

Let's Talk Purifiers: 'Water Cooled' & 'Non-Water Cooled'

Hi everyone,

No review today, but another ‘Let’s Talk’ article because I enjoy leaning about the tiny details that can makes the differences between a Strathmill and a Strathisla. Also, because I’m a huge nerd.
Purifier at Glenugie. 

So, Purifiers…
Turns out, I didn't know enough about them and what I didn't know was super interesting, that is, if you're a super interested self-styled whisky nerd like myself.

I had thought that Ardbeg and Glen Grant were the only ones to use them for one. False.
I also thought there was only one basic design. False again.

As it stands, there are 2 different types of Purifier (Water Cooled and Non-Water Cooled) and a total of 9 distilleries using them.

Distilleries using Purifiers-

Water Cooled
Glen Grant (Wash+Spirit)
Edradour (Spirit only)
Glen Spey (Spirit only)
Strathmill (Spirit only)

Non-Water Cooled
Ardbeg (Spirit only)
Glenlossie (Wash only)
Tormore (Wash+Spirit)
Scapa (Wash only)
Talisker (Wash only)

Glenugie (Spirit only) (1983)

Well then, what is a purifier?

A Purifier is a pipe linking the lyne arm back to the pot. The idea is to increase reflux by causing any heavy compounds or condensed liquid in the lyne arm to fall down the Purifier pipe and back into to the pot to redistill. Allowing only the lightest and most volatile compounds and alcohols to reach the condenser and spirit safe.
This, in theory, should result in a lighter whisky with less 'heavy' or 'oily' flavours.

The design varies from distillery to distillery, but most will have some sort of condensation area or jacket, then a pipe (Sometimes snaking or S-shaped like Glen Grant or straight like Strathmill) leading downwards to near the bottom of the pot still.
Purifier at Strathmill

The vapours that are coming into the lyne arm are a complex mixture of flavour compounds and alcohols, some of the less volatile compounds will condense in the lyne arm (depending on the angle, upwards or downwards sloping). The Purifier itself will then also condense any other less volatile compounds either through coming into contact with into relatively cooler and, in some cases, larger area of the Purifier chamber or by Water-Cooling. This liquid can then fall down the Purifier pipe and back to the liquid in the bottom of the pot to redistill.

Back in the lyne arm, only the lightest and most volatile alcohols and flavour compounds will be able to bypass the Purifier and continue to the condenser to be collected.

The amount of condensate refluxed will very much depend on the type of Purifier. A Non-Water Cooled Purifier will not condense as much vapour as a Water Cooled Purifier and therefore the product of the later will have a higher proportion of reflux. The Purifier pipe can be very thin (maybe 1cm in diameter), so I would assume that some condensate can also bypass the Purifier and continue to the condenser.

Because of the reflux occurring, the spirit coming off the still will be slightly higher strength than in usual pot stills but as distillation continues the strength of the spirit will fall anyway. The complex mixture of alcohols and flavour chemicals will have a higher proportion of lighter, more volatile compounds. This would include more esters that can be very fruity in flavour, and Acetaldehyde which some would say is 'sharp' and others 'ethereal.' You should also get less Feints and Fusel Oil being able to come through as those are much heavier and should descend back down the Purifier to be redistilled.

Of course, all of this is very dependent on a tonne of other factors, like size of the still, height of the still, volume of charge to the still, shape of the still, rate of distillation, type of heating, shape of lyne arm, angle of lyne arm, length of the lyne arm and the timings of the foreshots/spirit/feints cuts.
Purifier at Ardbeg

Some big questions remain though to me.

  1. How is Ardbeg still so peaty and oily, despite these flavour chemicals (Phenols, higher alcohols and fatty acid esters) being heavier? (I will concede that Ardbeg seems cleaner than Laphroaig or Lagavulin)
  2. Similarly, how is Talisker so peaty, oily but also spicy, despite using purifiers?
  3. Why does the consensus seem to be that Glen Grant matures very well? It normally seems that some heavier and harsher whiskies while young are the ones that are known to mature well (e.g. Macallan or Springbank).

I think a good deal of 1. and 2. can be explained by the fact that they are both using Non-Water Cooled Purifiers and only on 1 still. Of course, spirit cuts are going to make a huge difference as well. I think with Talisker, the sharp bends of the lyne arm and Worm Tub condensers will go a long way to capturing the oily and spicy flavours they look for. Ardbeg doesn’t have much of a chamber on the lyne arm for the purifier, just a pipe. This could mean that much of the condensed liquid could travel over the small pipe and down into the condenser, especially as they are downward sloping. They both also bottle at a higher strength, helping to preserve that oily feeling mouth feel.

Glen Grant I have no idea, I would have thought their lighter spirit from using Water-Cooled Purifiers on both stills wouldn't be able to stand up to long term maturation (25-50 years plus) in Sherry casks, which is what it is famous for. Anyone have any ideas?

Anyway, hope this has been another informative read. What do you think? Are my thoughts completely out? Do you particularly like whiskies from distilleries that use purifiers? Do you not really care who’s using them? Do you think it makes any difference at all?

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