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A Peek Into Diageo’s Cask Management — Dramming
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A Peek Into Diageo’s Cask Management

by Oliver Klimek on June 26, 2012

I already mentionend this in the report about the Malt Manaics 15th anniversary trip, the visit to several Diageo facilities proved to be very insightful with regard to how casks are managed by the company. Here are some interesting facts and observations, although not everything may be unique to Diageo:

First Fill Bourbon Casks

Bourbon barrels come disassembled on pallets which is easy to understand because there is much less volume to ship. There is a mildly interesting consequence, though. The barrels typically have 53 US gallons which is pretty much the same as 200 litres. But the Scottish coopers do not always just re-assemble the barrels (which are stacked one barrel per layer on the pallet), they also make bigger casks – the hogsheads – simply by using more staves. Of course this means many casks are made of staves from two or even three barrels. So the commonly used description “a cask that previously held bourbon” is not always entirely correct. Depending on how the barrels are prepared for shipping in the United States, a Scotch ‘bourbon cask’ may even have staves from different US distilleries.

Diageo prefers to use first fill bourbon casks for their grain whisky, so the bulk of all Diageo malt whisky is matured in refill casks. This is not very suprising because grain whisky makes up the biggest part in the cheaper blends (and those account for the biggest part of Diageo’s revenue). Young grain whisky is rather rough and edgy, so they want to make sure it gets the maximum of wood and bourbon interaction to help maturation.

Refill Casks – Mixing Things Up

Diageo has a very centralized system for handling casks, from filling to bottling. Newmake spirit usually is filled into tankers and then brought to the huge warehouse complexes like Blackgrange where it is filled into casks and stored. The warehouses on the distillery sites are part of that system, so they may contain whisky from any Diageo distillery.

When refill casks are used for malt, they may come from virtually any other distillery, the only thing that is taken care of is that caks which held peated whisky are not used for unpeated malt.

In a way this is a bit of a conflict between efficiency and consistency, the two principles regarded so highly by Diageo. Using only refill casks from the same distillery would certainly help the consistency of the products because there would be less differences between individual casks. But installing such a regime would certainly increase cost. And the increased variation among casks may not actually be a bad thing, especially for blended whisky. It adds a tiny bit of depth while not really disturbing the overall character.

But of course for single malts this means that essentially any bottling is likely to be ‘tainted’ by malts from other distilleries to a certain extent. And this may well be one of the reasons why single cask botlings of a distillery can vary very widely in character.

Cask Rejuvenation

Whisky casks can be refilled several times, up to five times I have heard for Diageo. This may sound horrendous, but you must not forget that casks can also be rejuvenated, and there is an entire production line at Cambus Cooperage devoted to this process. The decision if a cask is going to be rejuvenated is made by judging the colour of the whisky when disgorging. When it is deemed to light, the cask is sent to the cooperage where the inisde is shaved and re-charred.

In the past, rejuvenation simply meant removing the old char layer and applying a new char. But today a few milimeters of cask wood are shaved off befroe re-charring. This has the effect of activating more wood for maturation while taking away some of the whisky trapped in the cask wood. So a third refill could actually have more wood influence than a second refill but less influence from the previously held whisky.

Quantifying The Angels’ Share

I already reported about the cling film experiment Diageo did a few years ago. Regardless if the objective behind it was to reduce the angels’ share or not, it is not surprising at all that they think about this issue. One percent spirit loss per year may look neglectable, but when you own seven million casks this is a loss of 70000 casks per year. Assuming 200 litre barrels this means 14 million litres of spirit are lost every year, which is far more than the production capacity of Roseisle. Of course grain whisky makes up the bulk of this, but I think this makes it clear that reducing evaporation is a key objective for a distillery giant like Diageo.

Cask Selection? Not Really

Diageo are very serious about the quality of their spirit, the quality control by lab analysis and nosing is impressive indeed. Consistency, this magic little word, is the red thread connecting anything in the company. The spirit has to be as consistent as possible, the casks have to be as consistent as possible to guarantee that the whisky is as consistent as possible. Because it is impossible to select all casks to be bottled by proper nosing and tasting.

Diageo is all about blends, and this means Johnnie Walker first and foremost. A typical batch size for a Johnnie Walker bottling is 500 casks. This means a batch has the size of about 200000 bottles or 17000 virtual 9-litre cases as they are used in the production statistics (a real-life case of 12 0.7 l bottles has 8.4 liters, the 9 litres are based on 0.75 l bottles).

Now the entire annual production of Johnnie Walker (and this is mainly Red and Black label) is a whopping 18 million cases. This means 1000 batches per year. Three batches of 500 casks per day. How on earth could anyone select this amount by walking through warehoues equipped with a valinch and a nosing glass?

No, casks are ordered from the warehouse when they are old enough to be bottled. If the spirit has passed the initial analysis, it is assumed that after maturation the whisky is good for bottling.

How about batch variation in Johhnie Walker then? Well, even with Diageo’s thorough approach to spirit quality, no two casks are the same. But with batch sizes of 500 casks the differences will certainly level out.

But still this does not mean that one batch is exactly the same as another one. The smallest component going into such a batch can be as litte as a single cask! Let’s imagine it is a 12 yo second refill European oak sherry hogshead Auchroisk going into Black Label. Now from what we have just learned this could be a refill from Benrinnes for one batch and one from Glenkinchie for the next batch. Certainly there would be a difference. But can it be tasted in the bottling?


Of course this was just a little insight in how things work in such a huge company. It is understandable that on the scale that Diageo is operating on, compromises have to be made, and some inherent inconsistencies are not tackled by workflow organization but supposed to level out by the power of statistics.

Some other interesting questions remain unanswered so far, especially regarding sherry casks, cask manangement for single malts and treatment of casks that have not passed the newmake consistency test. But I have to say I have learned a lot during this visit anyway.

{ 9 comments… read them below or add one }

Michael June 26, 2012 at 8:34 pm

It’s interesting that a Caol Ila can be matured in a former (peated) Bunnahabhain cask and still be bottled as a single malt, but if someone dripped one tablespoon of Lagavulin into that Caol Ila it’s lost the single malt designation. (I think you may have written about this irony in a previous post or e-Pistle, but I’m still shaking my head.) I wonder how the SWA reconciles this paradox. Great article!


Oliver Klimek June 26, 2012 at 8:45 pm

Yes I mentioned this oddity in my first E-pistle to point out the stupidity of the legal requirements for single malts. Bunnahabhain is not very likely though, since it is not Diageo, but make that Lagavulin or Talisker and you have the reality.


Michael June 26, 2012 at 9:12 pm

Ah ha! Found the e-Pistle. Oops, I used your Lagavulin-Caol Ila example. Must have been subconscious! Thanks!


Ryan June 26, 2012 at 10:10 pm

So, do they do anything to distinguish between malts that are destined for blends and malts that are destined for single-malt bottling? Or, are they both pulled from the same pool of casks?


Oliver Klimek June 26, 2012 at 10:17 pm

This is one of the things that I failed to ask, but judging from what I heard there does not seem to be a special treatment for ‘single malt casks’, at least for the standard bottlings. But I am sure they pre-select casks for something like the Talisker 25 at some point during maturation. If anyone from Diageo knowledgeable about this subject happens to read this, a comment on this would be greatly appreciated.


Ryan June 27, 2012 at 3:55 pm

Now that I think about it, I guess if I had a “blended scotch company,” I wouldn’t want to admit that I was doing something “better” for the single malts and putting an “inferior” product into my blends. Thus, I would treat them equally.

As a fan of malts, I wish they had some nicer cask management for some malts, though!


Bigwxxl June 26, 2012 at 10:34 pm

In a Dutch whisky magazine there was an article about sherry casks how that works.
Get the feeling that cask selection is a big fairy tale, at least a big part of it.


Patrick Leclezio June 28, 2012 at 6:20 pm

“Diageo prefers to use first fill bourbon casks for their grain whisky, so the bulk of all Diageo malt whisky is matured in refill casks”. That’s a bit disturbing – especially if they don’t distinguish between malt for blends and for single malt bottling. Does the same apply to their sherry casks, and did they give you a more specific indication of what “the bulk” might mean? I understand that these casks are carefully managed and would be rejuvenated before they become too tired, and that there is no set of fixed rules to good blending, but there’s a certain comfort in a first-fill component to a single malt. Maybe it’s just my perception…


Oliver Klimek June 28, 2012 at 6:34 pm

As I wrote, the issue of sherry casks was not touched in the disussions, but I am sure they are used mainly for the malts. Sherry casks are just too expensive to use them for grains on a large scale. But we were specifically told that first fill bourbon is a priority for the grain whisky, and this corresponds with what I was told for example at my visit of Caol Ila.


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