Production

Give me strength

Ian Wisniewski looks at the effects of different filling and bottling strengths
By Ian Wisniewski
Choice is a wonderful thing, and that includes malts bottled at a comprehensive range of alcoholic strengths. This can be an important part of a
malt’s credentials, as well as influencing the flavour profile.The strength at which malts are consumed is a subsequent consideration. But long before that, the strength at which new make spirit is barrelled is another important factor.Filling barrels with new make spirit at 63.5% abv is a long-standing industry standard (adding water to the new make spirit, which comes off the stills at around 70% abv, adjusts the strength).Established by experience, this strength is widely considered to be an optimum balance between the rate of maturation, and the amount of casks, as well as storage space, required.Needless to say, there have always been exceptions, and in the 1980s, for example, there were instances of filling strengths above and below this level, with some casks filled at distillation strength during the 1970s. A practical reason for this was the continued growth in post-war production levels, until sales peaked in 1978, combined with a general shortage of barrels and limited warehouse space.Although lower filling strengths entail more casks (due to the increased amount of water added) and more storage space, some distillers believe this approach accelerates the maturation process.Meanwhile, fewer casks are required with higher filling strengths, though one theory states that this also means a longer route to maturity.However, it’s not simply a case of considering time and storage, as each option can also prompt a different range of reactions within the cask.As higher filling strengths comprise a higher proportion of alcohol to water, this can result in more alcohol-soluble flavour compounds, and fewer water-soluble compounds being derived from the oak.Correspondingly, a lower filling strength and so relatively higher proportion of water within the new make spirit, may see more water-soluble compounds being extracted.Exactly how this influences a malt in terms of flavour profile is hardly a straightforward chat, particularly as various filling strengths can produce
supreme results.Lower filling strengths can accelerate the removal of undesirable sulphur compounds, and increase tannin extraction (particularly from Spanish oak), which in turn promotes oxidation.Meanwhile, higher filling strengths may see an increased concentration of ethyl esters and acetal, promoting fruit notes, and “more of the wood components, including more vanillin more quickly, as well as caramel and woody flavours,” says Glenmorangie’s Dr Bill Lumsden.“My view as a chemist is that alcohol is quite a good solvent so at a higher strength there’s a greater solvent effect, and the alcohol solublises more of the wood components which leach out into the spirit.“However, this is often at the expense of other maturation reactions as the strength goes up, eg. cask oxidation.”Consequently it can also be a case of establishing a different equilibrium within the cask.“A lot of it is not to do with specific compounds, but the mix and interaction of these compounds,” adds Alan Rutherford, visiting professor of distillation at Heriot-Watt University.Assessing how influential a different equilibrium may be is the next stage. Jim McEwan of Bruichladdich adds: “I don’t think there are significant differences between spirits filled into the cask at 63.5% abv against spirit filled at full strength 71.0- 72.5% abv. The 63.5% abv was really an
agreed filling strength used by the major distillers when reciprocal filling contracts were being agreed.“If it was a quality issue it’s beyond belief that all distillers just happened to arrive at the same conclusion that 63.5% was best,what about 64.1% or 62.9% abv, never seen that in 40 years.”The filling strength at Bruichladdich has been 71-71.5% abv (distillation strength) ever since the current owners reopened the distillery a few years ago.“Nor do I believe that maturity is any quicker by diluting more. I’m sure full strength whisky will mature just as quickly,” adds Jim.Bruichladdich is in a minority filling what will be single malt bottlings at a higher strength. Some other distilleries also barrel malts at higher strengths, such as 68.5% abv, which can be used for blends.Another aspect to consider is whether different filling strengths influence the evaporation rate during maturation, which typically accounts for 2-2.5 per cent of the contents of a barrel per annum. Even though the influence of evaporation rates on ageing is still not fully understood, it’s
always worth posing the question.“Component reactions will change due to filling strengths, you’ll get a higher evaporation rate at a higher strength, but this also depends on the storage conditions,” says Ewen Mackintosh of Gordon & MacPhail.And Jim McEwan adds: “If there is higher evaporation at a higher filling strength it’s marginal. The warehouse environment is more important. By filling at 63.5% abv, and losing on average one per cent alcohol per annum as a rough guide, you will not make great ages.“Filling at 71% abv you’re adding seven years of longevity from the start. I want Bruichladdich to make 40 years comfortably, and with a good quality cask stored in a dunnage warehouse by the ocean it should be fine.”Once casks are pronounced mature by the master distiller, a subsequent decision is the bottling strength. The minimum strength of 40% abv was established as a result of research, which showed that character and quality can be compromised at strengths below 40% abv. Consequently, 40% abv is a practical choice, enabling the maximum amount of stock to be bottled.While the traditional strength for export markets was 43% abv, various malts are available at this strength on the British market. And with malts at 40% abv also exported to numerous countries, this distinction hardly applies anymore.Whether another key strength, 46% abv, represents an optimum in terms of flavour delivery is one consideration.“If you don’t want full cask strength whisky, bottling it at 46% abv gives you a nice comparison to a 40% abv spirit, with increased presence on the palate,” says Ewen Mackintosh.But 46% abv is also the lowest strength at which malt can be bottled without having to chill-filter (whether, and to what extent, chill-filtering can affect texture and flavour is an ongoing debate). Needless to say, malts featuring the term ‘non chill-filtered’ exert a considerable allure on connoisseurs.Cask strength bottlings vary from a high of around 65% abv, to just above the legal minimum of 40% abv. There’s also the case of ‘roving’ cask strengths, in the case of a permanent-line such as A’bunadh.Bottled in batches, A’bunadh’s strength ranges from 59%-61% abv which means the flavour can vary slightly, enabling fans (including me) to savour every edition.Consequently, as distilleries continue to extend their portfolios, and demand for a broader range of bottling strengths keeps growing, various criteria can influence the question of ‘what strength?’“At the connoisseur end of the market 40% abv is almost considered a negative factor, with demand for high strength whiskies driven by the perception of a more natural product,” says Ewen Mackintosh.How things have changed. During the 1980s when Gordon & MacPhail offered the same malts at three different strengths, 40%, 46% and 57% abv.“The real seller was 40% abv, and throughout the 1980s the higher strengths were discontinued. Cask strength malts were introduced in the late 1980s, as demand was growing for natural from the cask bottlings,” adds Ewen Mackintosh.Conducting a ‘compare and contrast’ tasting is still possible, as Gordon & MacPhail offers three versions of a Glenlivet 15 year old at 40%, 46% and 57% abv. As independent bottlers need to offer a point of difference from proprietary brands, ‘alternative’ bottling strengths are a means of achieving this.And that raises a final consideration, a malt’s ‘glass strength.’ The usual line in praise of dilution, that it makes a malt ‘more accessible,’ doesn’t tell the whole story.As adding water lowers the alcoholic strength, this also changes the flavour profile, rather than the ‘original’ flavours simply becoming more accessible. I’m not a diluter, but then I’m not a dictator either, and whether a malt blossoms when diluted is a matter for each individual palate.One reason for my abstinence from water is that I consider texture to be a vital part of the whole dram tasting experience, whereas the only adjective I can apply to diluted malts is ‘watery.’Inevitably, I’m more flexible with cask strength drams, but some of these can offer amazing delicacy on the palate, which would be unknown if diluted.Jim McEwan’s dilution philosophy is to add progressively less water to older malts, up to a 30 year old. After that he adds no water, but allows the whisky to breathe.“You should also allow one minute for each year of aging, by which I don’t mean looking at a 30 year old for 30 minutes, but then allow 30 minutes in which to enjoy it,” he says.“Keep nosing and tasting, and see how it keeps changing.”