Producing spirits requires phase change: We must add heat to the fermented media to create vapor from the most volatile compounds, and we must then remove energy from the vapor to create condensate.
This is an energy-intensive process, and for the heating phase, distillers have multiple options depending on their size, desired output, and local zoning and other restrictions.
Steam
The most common method to heat a still is by using a low-pressure steam boiler, running steam either to the still’s jackets or to a steam coil inside the still. Natural gas or propane heats the water in the steam boiler; the steam-to-distillate heat transfer produces the condensate, which is then pumped back to the boiler, reclaiming the heat and reusing the water.
Steam is an efficient heating medium, and we can apply it in a controlled, calibrated manner, gently raising the temperature of the distillate and reducing the likelihood of scorching. We can also adjust during the run to distill more aggressively or more gently, so that we can fine-tune the flow rate.
However, boilers can be expensive to purchase and install, and they require regular maintenance to stay in peak form. Because boilers have the potential to fail and explode, they’re more highly regulated than other options and may require a dedicated room or other safety considerations, depending on your distillery’s jurisdiction. However, a well-maintained boiler can be consistent and reliable—they’re the workhorses of many distilleries around the world.
Electric
At the smaller end of the spectrum, internal electric elements are also an option.
While much more affordable than installing (and maintaining) a boiler to provide steam, electrical elements are limited in the volume they can heat, and they can tend toward scorching if not managed carefully. (All heating options have the potential to scorch and cause caking when aggressively heated, and/or when distilling a mash with a high proportion of solids or highly viscous compounds—but some approaches have a greater tendency than others.)
While designs vary, heating elements can be run on 110- or 220-volt power, whereas an industrial steam boiler often requires a 480-volt or 240-volt, three-phase power source. There’s a limit to how much heat individual electric elements can provide—i.e., how much mass they can heat up—but they’re scalable to a certain extent with the addition of more heating elements.
However, at a certain point—often around 100 gallons, but highly dependent on many other choices that the distiller and still designer make—an electric setup draws an excessive amount of power through the number of elements needed while still taking hours to bring the distillate up to a boil. That’s why electric is a better fit for smaller stills.
For new distillers, one upside of electric stills is that some manufacturers have been able to create programmable, modular equipment that—for better or worse—reduces the level of knowledge required to run the stills. These programmable stills allow the operator to choose from a menu of preset programs, automating much of the distilling process.
Direct Fire
Some distillers continue to use direct-fire heating to run their stills—which is, of course, the most traditional approach to distillation. The romantic image of the master craftsman carefully stoking and managing the fire to maintain the right temperature in the still is an alluring one.
In reality, modern direct-fire stills generally consist of a gas burner surrounded by a circular wall of fire bricks, which retain as much heat as possible below the still. Besides the specialized heating apparatus, the still itself needs to be specially designed to withstand direct fire, which is harder on the surface than other heat sources. Thus direct-fired stills generally rely on copper bottoms rather than the otherwise more durable stainless steel.
Adherents of direct fire describe a flavor profile that they couldn’t achieve with other methods, a complexity resulting from the creation of high-temperature Maillard reactions and caramelization in the still—reactions that steam and electric heating can’t provide. Those reactions are the result of the higher temperatures driven by the direct flame.
However, if not carefully designed and managed, direct fire can also lead to uneven heating, hot spots, and scorching in the pot—not to mention the safety risks of having an open flame directly beneath a system filled with flammable vapor. Many jurisdictions won’t even consider permitting a direct-fire still because of the potential danger.
Thermal Oil
A more modern but uncommon approach is the use of thermal oil.
In this case, we would heat the thermal oil separately then circulate it through the still’s jackets, or through an external calandria—a heat exchanger in which oil heats up the wash as they both pass through it.
While thermal oil can’t reach the same temperatures as direct fire, it can still get hotter than steam or electric elements—hot enough to cause some caramelization and Maillard reactions.
Although thermal-oil systems haven’t become widespread in beverage-alcohol distilling, a handful of distillers have tapped into their potential. They’ve also gained a foothold in the petroleum industry because of their lower operating pressures and ability to achieve higher temperatures, among other factors.
Warming Up to the Best Heating Method for Your Distillery
For many distillers, budgetary, regulatory, or infrastructure constraints will narrow the choices available.
For example, a rural distiller may not have access to natural gas or propane, while one in a busy downtown area might find their code-enforcement agency applying prohibitive safety requirements for a steam boiler or for equipment above a certain size.
In all cases, you’ll need to calibrate the capacity of the heating system to the needs of your distillation equipment. An undersized heating system might save you money initially, but it will cost you in the long run if the still takes hours to heat up, or if it’s only barely able to maintain enough energy to complete a distillation.
An engineer can calculate how much heat the system needs to provide, as well as some buffer capacity and any additional load, and estimate the needed sizing and specifications. A few things to consider:
- Will the same system be heating both the still and a hot liquor tank at the same time?
- Do you expect to add a second still in the future?
- Will there be other major demands on the electrical panel that feeds the heating elements, such as milling and grain conveyance?
As previously mentioned, regulations can be a significant limiting factor and are highly variable. You may be working with a municipality on one side of the road or a county on the other—and both jurisdictions could have vastly different statutes on the books, as well as different interpretations of the National Fire Protection Association code.
As a result, the available options are often a confluence of what meets your technical needs and what satisfies the local regulatory requirements. Keeping an open line of communication with an engineer and the local authorities is invaluable, and it can save tremendous time and money for the new or growing distiller.