You purchase a cask of whisky and are excited about the prospect of bottling it in the future. Years of expectation. You bottle it. What happened? Why are there only 100 bottles? The person who sold it to me promised me I should get 240 bottles!
Owning a cask of whisky should be exciting. It should be fun. In the first (poor quality) website I ever built on Microsoft Publisher in 2010, it was mentioned as the key aspect of any purchase. If you can do it with friends, even better. Spread the cost, spread the risk.
The problem that is arising these days is that while £1,000 spread over 10 years can be a bit of fun, £10,000 is a bit more serious. A few litres lost doesn’t make much difference when it cost you £10 per litre all those years ago, but a few litres lost at £300 per litre is a very big deal.
Whether we’ve sold the cask or not, as a bottler, we often find ourselves bearing the brunt of the anger of a cask owner who is annoyed about the outturn of their cask. So here is an attempt to explain a lot of the reasons why you might lose liquid.
- Leakage. It happens. We wish they didn’t leak, but the casks are made from wooden staves which have gaps between them, so inevitably you’ll get some which don’t swell up properly and allow the liquid to leak out. The casks will also swell and contract according to the seasons as the wood warms and cools. We find that in February we can open a cask and the liquid will be down around 5-7 degrees Celsius. In the Summertime is can be up at 15 degrees C. The liquid absorbs heat much more slowly than the surrounding air, so even if we have a few weeks at 25 degrees C, the whisky doesn’t immediately heat up. So walking into the warehouse in summer is like walking into a fridge. In the winter time, the whisky stays warmer than the air it can be a balmy 7 degrees in the warehouse when outside is 0 degrees. As usual, I’m digressing. The point is, some casks leak in winter, some casks leak in summer, some drip occasionally, some split and empty their entire contents. It won’t make you feel better as an owner, but mathematically, a 3ml drip once per minute will empty your 200 litre cask in 46 days. A 3ml drip might not even make it to the ground for us to notice. If it does, it might evaporate before we see it, or pool underneath the cask so that it isn’t visible. We don’t like seeing leaking casks and will do what we can to fix them when we see them (usually we rotate them in the racks until we get a chance to remove them). A good way of telling if a cask has leaked or evaporated is usually to look at the strength. If it is low in content but still high in strength, it has probably leaked. There are variations on this depending on the time that has passed, but it’s usually possible to make an educated guess.
- Evaporation. It is commonly accepted that casks will lose 2% of the alcohol. I’m happy to go along with that, but if you’re in the business of buying and selling casks you need to know that you’re oversimplifying if you state this to people who are purchasing from you as if it is a certainty. If you’re filling a new cask or a dry one, you’ll lose much more in the initial few months as the cask soaks up the liquid. We have wine barriques regularly weighing 4kg more when we empty them than we we filled them, despite waiting for every last drop to come out. There are other issues which I’m not smart enough to prove, but it seems clear to me that if you have a full cask, less will evaporate than if it is half empty, much like the strength reduction that takes place in a half full bottle as the whisky evaporates. In addition to this, if your cask is half empty, this means that the top half is dry, and consequently not swollen by liquid. This means that the wood must be more porous or have larger gaps between the staves, so evaporation will be higher.
3. Bottling losses. We’ve done everything we can to make sure that these are as small as possible, but they still happen. First, the contents of your cask will include varying amounts of solids. This is usually insignicant to the point of not being worth mentioning, but for some heavily charred first fill bourbon barrels, a kilogram of wet charred wood can come out of the cask. We’ve taken a gross weight and an empty weight of the cask, so this charred wood will have been included in the weight of the liquid, but must be filtered out. Therefore it is included as part of the losses.
We currently try to filter the whisky as little as possible, but it is causing us significant problems with more fatty whiskies (sherry and wine finishes the main culprits). We have a bag filter to catch all of the solids (think pillowcase but finer), followed by a couple of other filters to take progressively finer solids out. The more filtration you do, the more flavour you lose, but also the more liquid is lost within the filters. As most of our bottlings are single casks, we try to collect the liquid from the filters at the end and put them into one or two bottles that are kept separate from the rest. They are likely to be dirtier and require filtering by hand later. In the initial tank and filters I think we probably lose about a litre in total.
There will be further “losses” if you ask for the whisky to be reduced in strength before bottling. These are not real losses, but mathematical ones. For example if you have 200 litres at 60% vol. and you ask us to reduce the whisky to 46% vol., we will be required to add 60.86 litres of water. The reality is that we’ll do this in stages- 30 litres, mix, check the mathematics, 25 litres, mix, check the mathematics and so on, with smaller increments as we go. Eventually we’ll reach a point where we maybe have to add 200ml of water to reduce the whisky from 46.189% to 46.054% or something like that. We don’t risk it. We leave the whisky at 46.189% and forget about the 200ml of water. Your whisky will still say 46.0% on the label, so the difference is recorded as a loss. For this reason, it’s always easier to just bottle at cask strength. We write down what the strength is recorded at and assume that we’ll stay within any tolerances allowed by Trading Standards.
The majority of bottling losses come in overfilling of bottles. If we put 4ml extra into a bottle, then over a 250 bottle cask you’ll lose another litre. There will likely be about 100ml lost within our bottling line, as we empty all the pipe backwards at the end of each run, to be added to the couple of bottles that are collected out of the filters.