Reaching maturity is a major event in the life of a whisky, leaving a cask that has been home for years and preparing for marriage. Various approaches are used to promote marital bliss, depending on the master distiller or blender presiding over the ceremony. Some are more pragmatic than others, but, as with each stage of the production process, the real issue is not whether one approach is more complex than another, but how this helps to achieve a particular expression.Although marrying tends to be associated with blended whisky, the same principle applies to single malts, which comprise a ‘recipe’ of different casks and maturation influences. The focus of marrying tends to be the period once whiskies have been transferred from marrying vats into marrying casks (more like a honeymoon), to integrate and harmonise at leisure. However, ‘marrying’ can also refer to the overall process of combining mature whiskies.Malts are introduced to each other within marrying vats (large vessels, also known as marrying tuns or holding vats), on a scale that varies from a couple of casks to over 100. This experience can last a matter of hours, or extend to several days.Whether the vat is stainless steel or oak doesn’t generate much of a debate. Apart from the minimal time scale involved, the oak is inactive, while the advantage of stainless steel is essentially ease of cleaning.Malts are typically (though not always) combined at cask strength, with rigourous cask selection identifying any significant variations in strength, which can obviously affect consistency.“Due to age and the natural way casks mature, strength variations can occur – for example, our 12-year-old can vary from the low 50% abv to low 60% abv,” says David Robertson, The Macallan’s master distiller.“At The Macallan, the vat strength is always reduced to 46.5% abv, achieved by adding demineralised process water from our wells to the whisky in the vat. The marrying strength is important to help promote flavour consistency. Sensory trials have indicated that at this low strength we get a more even and successful marriage.”Another established method of promoting consistency is to retain a certain amount of an existing marriage within a vat. For example, a 100,000-litre capacity vat may retain a minimum 50,000 litres of an existing marriage, into which additional casks are emptied. Batches of whisky can subsequently be drawn from the base of the marrying vat (while maintaining the minimum level).To ensure thorough integration of component malts, vats can be fitted with a rouser (resembling a propellor). Alternatively, whiskies can be drawn off from the base of the vat, and then ‘re-circulated’ by pumping them back in at the top of the vat.The flavour profile of a malt undergoes a certain evolution within the marrying vat, which stems from the interaction between component malts. This sees some characteristics being promoted and others relegated, in the course of reaching a new equilibrium (reflecting the fact that even the same type of casks filled with the same batch of new make spirit and aged next to each other in the same warehouse will show differences, sometimes minor, sometimes major.)Consequently, a spell in the marrying vat may be considered all that is required prior to bottling. But agreeing on that point doesn’t mean there aren’t different approaches to vatting.At Gordon & MacPhail, the traditional approach is reducing strength in the marrying vat to within one to two per cent of the bottling strength by adding demineralised water. Remaining in the vat for 10 days, accompanied by periodic rousing, it is referred to as leaving malt ‘under water.’“This gives the whisky time to marry with the water, which helps to mellow it out and give a certain smoothness. The longer it’s under water, the better for the bottled product. There are subtle differences between malts, according to the period of time they are under water,” says Ewen
Mackintosh of Gordon & MacPhail.Returning malts to marrying casks after vatting also raises the question of the duration of the marrying period. As this varies not only among distilleries, but also among different expressions of the same single malt, there is no uniform timetable.One theory is that more mature malts, and more complex recipes, require longer marrying, whereas some distillers believe that more mature malts marry more readily, and need less time. Meanwhile, another opinion is that younger malts (eight years or less) require a longer marrying period, to achieve a general ‘smoothing’ effect.At Gordon & MacPhail, certain malts such as Benromach are filled into marrying casks. Malts are initially reduced to within 3 to 4% abv of the bottling strength in the marrying vat, prior to a marrying period that typically lasts at least three months.“These are refill butts, but they’re not completely inactive. There is a small degree of maturation coming through,” adds Ewen Mackintosh.Marrying casks are vatted, with one third of each marriage cycle retained and vatted into a subsequent batch for consistency. Meanwhile, inactive oak is a standard choice for marrying casks, but that still praises the question of what actually happens during that time.Malts assembled for The Glenfiddich 12-year-old, for example, are transferred from a stainless steel marrying vat, still at cask strength, into inactive oak marrying tuns with a 2,000-litre capacity. A four month marrying period takes place in the marrying warehouse, which provides a
similar environment to a traditional dunnage warehouse.“There is a slight difference between the whiskies when they are in the stainless steel vat, compared to four months later when drawn from the marrying tuns. As the whisky settles, it smoothes and rounds off, though no new flavours develop during marrying. The real benefit for us is the ability to mix different vattings from these tuns, to go forward for bottling to achieve consistency,” says David Stewart, chief blender, William Grant & Sons.The Macallan’s choice of marrying casks are effectively third-fill sherry butts, filled for a minimum of three months, though in some instances the marriage may extend for six to 12 months. This yields some subtle, but significant developments.“There’s very little wood extractive influence, but we get a little oxidation taking place. The malt doesn’t gain any flavours it didn’t have at the start, but it does gain softness, harmony and a level of complexity. And the longer we give them to marry, the smoother and rounder the whisky,” says David Robertson.The various maturation influences behind Glenfiddich’s Solera Reserve make this an ideal case study. But first let’s recap on the recipe. This expression combines a high proportion of malts aged for 15 years in bourbon and refill oak, together with malt aged for the same period exclusively in sherry casks, as well as malt aged for 15 years in bourbon and refill casks subsequently finished for three to four months in new oak.Casks of each component malt are vatted separately and transferred for a spell in marrying tuns, before being vatted together in the solera vat, which remains at least half full with an existing marriage. Malt drawn from the solera vat spends up to four months in marrying tuns. To promote consistency, the contents of several marrying tuns are revatted, and then it’s ready for reducing and bottling.While it takes two to make a marriage – a distiller and the whisky – there are far more ways to make it work. And whatever produces the desired result has to be the right choice for each couple.