Whisky distillation has been an art for a very long time, and it has always relied primarily on the raw power of fire. In the centuries prior, direct-fire heating was used in all whisky stills around the world. A technique that was superseded by more manageable alternatives such as steam pans, coils, and, more recently, external heating systems. In 1887, Glenmorangie made history by installing steam heating in its stills for the first time in any Scotch malt distillery.

Relying on Time-Tested Strategies

Some distilleries, including the illustrious Glenfarclas, Glenfiddich, and Springbank, still use the antiquated direct-fire heating process. Until early 2019, when it switched to direct electricity, Dornoch also employed this method. In our modern, technological age, this practice may seem antiquated, but these distilleries insist it’s what gives their whisky its distinctive flavor.

Traditional Methods of Whiskey Production and Distillation

The process of whisky production is an intricate and layered affair, deeply rooted in time-honored traditions. Some distilleries hold steadfast to these methods, believing them to be an integral part of the whisky’s character and flavor. Let’s take a stroll through this conventional process, from barley to barrel.

Malting the Barley

In the traditional process, distilleries start by soaking the barley in water for several days to trigger germination. This step, known as malting, creates the enzymes that convert the barley’s starch into fermentable sugars. Once germinated, the barley is then dried in a kiln. Peat, a decayed vegetation matter, is often burned during this drying process, contributing a distinct smoky flavor that’s characteristic of many Scotch whiskies.

Mashing and Fermentation

The dried malted barley, now called malt, is then ground into a coarse flour known as grist. The grist is mixed with hot water in a large vessel, often made of wood or stainless steel, called a mash tun. This process, known as mashing, dissolves the sugars in the malt. The liquid part, known as wort, is then separated and moved into a fermenting vessel called a washback.

Yeast is added to the wort to kickstart fermentation. Over several days, the yeast consumes the sugars in the wort, converting them into alcohol and creating a liquid known as “wash,” similar to beer in strength and flavor.

Distillation in Pot Stills

Traditionally, distilleries use pot stills for distillation, a process that happens in two stages. The wash is first distilled in the larger wash still, producing a liquid called “low wines.” These low wines are then distilled a second time in the spirit still. The distiller cuts, separating the “head,” “heart,” and “tail” of the spirit based on the alcohol content and flavor. The heart is the portion that continues onto the next stage.

Maturation in Oak Barrels

The heart of the spirit is transferred into oak barrels for maturation. Traditionally, distilleries use barrels that have been used previously to age sherry or bourbon, which imparts additional flavors and aromas to the whisky. Over time, the whisky also draws flavor from the wood itself, while the porous nature of the barrels allows the spirit to breathe, slowly evolving the character and complexity of the whisky.

From malting the barley to maturing the spirit, these traditional methods represent the heart and soul of whisky production. And for distilleries like Glenfarclas, Glenfiddich, and Springbank, adhering to these methods is an essential part of creating their distinct and cherished whisky expressions.

 The Unmistakable Taste of Direct Fire

The ‘weight’ of flavor is often cited as the reason that distilleries that use fire-heated stills insist on sticking with an antiquated method. For instance, in 1981, Glenfarclas tried using steam heating but quickly switched back to direct fire after seeing a decline in the whisky’s flavor.

Suntory abandoned steam heating in favor of direct fire heating in the wash stills of its Yamazaki and Hakushu distilleries in search of the ephemeral attribute of “weight.” The firm made this unexpected and countercultural choice because it believes that direct fire distillation results in a richer and more nuanced flavor in new-make whisky.

Direct-Fired Stills Have a Unique Layout

Direct fire stills are easily recognisable by their distinctive convex base that promotes equal heat distribution from the gas fire. Stills need thicker copper walls because of the high temperatures generated by direct burning. The stills also have a rummager, a chain that cleans the copper as it spins around a gear shaft, to reduce the possibility of burnt odors.

The Chemistry of Taste

Super-heating and charred yeast have been cited as possible contributors to the flavor of alcohol produced in fire-heated stills, but the exact mechanisms by which this occurs are unclear. I.   Similar to how a steak begins to brown when placed on a hot griddle pan, this can cause a Maillard-type reaction. Flavor compounds such as furfural, which has a caramel and nutty aroma, can be produced in this reaction, along with sulfur and vegetable overtones.

Risk and Flavour: Striking the Right Note

There is a fine art to balancing the possible flavor gains against the hazards. More common in coal-fired stills, ‘hot spots’ are caused by the intense heat generated by the direct flame. These were used at distilleries like Ardmore to give its brandy or whisky a unique flavor. However, replacing coal fires with steam and gas heating makes regulating the boiling rate simpler, which reduces the likelihood of hot patches and eliminates overpowering burnt odors.

Its Promising Future

A natural concern that emerges as whisky production techniques develop is whether or not direct-fire heating will be adopted by more distilleries than the few that currently utilize it. Suntory’s chief blender Shinji Fukuyo responds to questions about reintroducing direct fire to their Scottish estates by saying that while the company is always looking for ways to improve the quality of their whisky, the introduction of direct fire must be weighed against other factors like cost, environmental impact, and health and safety.

While not the most scientific or controlled approach, distilling whisky with direct fire heating has an inherent allure for those distilleries that still use it and the whisky lovers who appreciate the flavors it provides. Like any craft, whisky creation entails trade-offs, and for distilleries like Glenfarclas, Glenfiddich, and Springbank, the appeal of direct fire’s rich, complex flavors far surpasses the difficulties of the process. According to Shinji Fukuyo, the use of direct fire in the production of whisky is uncertain. Time will tell if this age-old method finds new relevance in today’s whisky industry.