A marriage should benefit both partners, or multiple partners in the case of a blended Scotch. The ceremony, administered by a master blender, culminates in the blend being filled into 'marrying casks' for what is effectively a whisky honeymoon.
Marrying regimes vary significantly, even among blends within the same company, but the objective is the same. “Marrying unifies the flavour rather than changing it by creating harmony, balance, roundness and, most importantly, consistency,” says Brian Kinsman, master blender at William Grant & Sons.
Malts are initially blended separately from grain whiskies in vats (large vessels) before all are vatted together. When whisky is added to a vat, it settles on the surface rather than integrating with the whisky already present, a process known as layering. To counter this, vats are fitted with accessories that integrate the whiskies.
One option is impellers, which rotate like propellers, located at the base of the vat. Sensors inside a vat monitor the level of whisky being added – when this is sufficient to cover the impellers, these are switched on by the sensors. In a vat with a capacity of 150,000 litres, for example, sensors are activated at 3,000-4,000 litres.
Alternative options include paddles on the sides of the vat, which move back and forth, and air rousing, blowing air from the base so it rises to the top. Larger vats tend to use air rousing, while some vats combine this technique with impellers.
At Chivas Brothers, where the vats range from 2,000 to 200,000 litres in capacity, minimum rousing times vary. Director of blending and inventory, Sandy Hyslop, explains that the process depends on a number of factors: "Some [vats] have a horizontal orientation, and some are vertical; some fill from the top, others from the bottom."
Integrating component whiskies is a practicality, but also a creative process, as The GlenAllachie's master blender Billy Walker explains: “Whiskies remain in the blending vat for a couple of weeks, and this period of integration in itself contributes to the final flavour and character."
The usual criterion for a marrying cask is being ‘inactive’ following extensive usage, while the whisky within remains active.
“I’m not looking for the whiskies to draw anything from the cask, but still to have interaction with the surrounding atmosphere which promotes an overall integration of flavours,” says Dewar’s master blender Stephanie Macleod.
Some marriages last longer than others, and finding the optimum for each blend is vital. For the Dewar’s Double Double series, for example, malts and grains are married separately for one month, then together for the same period.
Stephanie says, “It really makes a difference, bringing everything together. Dewar’s Signature is a complex blend married for three months, making it rounder, smoother and more integrated. We also experimented with four-, five- and six-month marrying, but there were no further benefits."
The reason for varying schedules is the scale of flavours, rather than the age of the whiskies. A more complex blend with bigger, bolder flavours, such as one spanning phenolics and sherry notes, takes longer. But the schedule can also be influenced by external factors; seasonality, for example, can make a difference during the marrying period.
“When it’s cooler over winter in the ageing warehouses, everything will happen more slowly than in the summer, when the temperature is higher,” says Diageo master blender Emma Walker.
The key question is not just whether vatting and marrying can create an equilibrium of existing flavours, while also revealing previously masked ones, but also whether any new flavours can be created. These changes are not measurable analytically, but that’s more about the sensitivity of the instrumentation available, though changes can be assessed by a nose.
Brian Kinsman at work
Brian Kinsman says, “For sure, there’s interaction with small transformations creating new flavour compounds. Even if not discernible, these flavour compounds can still be contributing behind the scenes."
That’s the challenge: to quantify change. If a recipe comprised one malt and one grain whisky, it would be easier to track changes to the flavour profile during marrying.
Another influence that is difficult to quantify in a longer marrying process is oxidation. A test case is Johnnie Walker Master’s Edition, a 50-year-old blend that underwent longer-term marrying over a number of months. Emma Walker says, “Oxidation can continue during marrying, which in principle can result in more complex whiskies with additional characteristics."
Similarly, evaporation plays a role. The Last Drop 50 Years Old includes whisky which has already experienced a long-term marriage. The recipe includes casks of blended Scotch of different styles, which may have been marrying for at least 30 years.
Colin Scott, master blender at The Last Drop, says, “During this time there would have been some cask influence, as well as evaporation, increasing the intensity of the flavours.”
Cask influence can of course be intensified to achieve the desired result, as with Grant’s 12 Years Old, which is married and finished for two to four months in active second-fill bourbon barrels. Of this process, Brian Kinsman says, "It adds subtle vanilla and some sweetness which further enhances the already-unctuous mouthfeel."
The GlenAllachie's White Heather 21 Years Old also includes whiskies vatted then filled into active casks including new American oak, red wine and Pedro Ximénez. As marrying lasts at least two years, this process incorporates additional maturation.
“We’re essentially blending cask types rather than malts and grains," Billy Walker says. "Each batch of White Heather won’t be exactly the same, but will have a similar profile: very smooth but with an excitingly rich and bold flavour including sherry notes, dark chocolate, mocha, heather honey and vanilla."
A universal practice is sampling at every stage, from the arrival of the casks to the bottling line, and equally universal is retaining samples, just in case. At William Grant & Sons, new-make spirit samples are kept for a year, blends and vattings for three years, and final bottling samples for five years. All are stored in a dedicated warehouse, and Brian Kinsman has some 50,000 samples just in his part of the building.
By regularly comparing each new batch with those that came before, blenders ensure their whiskies have long and happy marriages which deliver consistency of flavour.