Still Anatomy 101: Exploring the Anatomical Depths of Batch Distillation

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Stills are special vessels – they have this ability (superpower, really) to turn this slightly acidic, alcoholic, carbonated liquid into a more refined, adult version of itself. For some it is just a shiny pot with a funny arm, used to produce alcohol with a higher water content; although this is not wrong, stills can be very diverse. Available in a range of heights, widths, shapes and materials – from round to square, squat to large, and copper to clay – each still can have its own character. Some might even have unique damage or bumps that the distiller thinks is the “secret sauce”.

Many of these characteristics can impact the process or flavor profile of alcohol. Either way, the still is the heart and soul of the distillery and their uniqueness should be celebrated. However, certain components are essential for operation, which can be categorized into: safety, practicality and heating, reflux and flavor development, and condensation and collection. Granted, there can be variation within each category, and this is what makes distillation such an exciting business.

However, there is one area where minimal variation should exist – security.

Westland Distillery Inspired by Scottish tradition, the Westland Distillery in Seattle uses pot stills. (Image copyright The Whiskey Wash)

Security

Distillation is an inherently dangerous process. Heating a solution to remove and concentrate the alcohol by vaporization creates the risk of fire and explosion. Therefore, the equipment should be designed and operated by qualified professionals to prevent such events from occurring. In addition, the distillery must have standard operating procedures (SOPs) to ensure proper and safe operation of the equipment.

Apart from fire extinguishing systems, SOPs and facility layout, still design should incorporate a few key elements to minimize the risk of explosion or collapse. Pressure Relief Valves (PRVs) are spring loaded safety valves designed to release excess pressure to the atmosphere when its set point is exceeded. However, one must also consider the flammable vapors inside the still and what could happen when they are released. Anti-collapse valves (ACV) are installed to prevent collapse due to the formation of a vacuum.

Although activating the ACV poses less of a risk to the operation or safety of stills, it signals the occurrence of an event that could damage the still. These valves are essential to minimize the risk of explosion, damage to equipment and property, and injury to personnel. However, safety does not end there and must be integrated into all aspects of the design and operation of the still.

A drawing of the structure of a still image (image via Liz Rhoades)

Practical features and heating

In addition to the loading and unloading lines, the manholes are another essential element; it is a medium sized opening with a sealed door that allows for cleaning, inspection and maintenance activities. Although it looks like an entrance, stills are not designed to have people inside and only trained professionals under strict supervision should enter. When done improperly, entering the still can pose serious safety risks and violate safety regulations.

The sight glasses provide a window into the soul of the still, giving the still valuable insight into what is going on inside. For example, during this initial distillation, foaming can occur inside the still due to the charge of the still containing many particles (yeast and / or cereals) and dissolved carbon dioxide; the sight glass gives the still visibility to prevent flare-ups.

Excessive foaming can lead to entrainment (ie “throwing up”) of solids or liquids in the passing vapor and alcohol, which has a negative impact on quality. When observed, the still can mitigate entrainment by reducing heat input.

Heating methods have evolved as the industry has developed and two main types are used: direct and indirect. Direct fire is a more traditional practice, where more archaic fuels include the use of wood or charcoal. Although direct fired stills are still in use, most have been improved to become more efficient gas burners or electrical elements.

Indirect fire uses steam as a means of heating, usually supplied by coils and / or pans inside the pot. Steam is generally preferred due to increased safety, improved consistency, and increased operational efficiency.

Although direct fire has some advantages, such as creating unique flavor profiles; this is due to the localization of heat and its intimate interaction with the components of the wort or beer. In fact, some distilleries tried to go steaming, but quickly returned due to a change in flavor profile.

Although important, the heating method used plays only a lesser role in flavor development, especially when compared to those elements impacting the level of reflux and rectification.

Virginia Distillery Company

Handcrafted copper stills by Virginia Distillery Company (image via VDC)

Reflux and flavor development

During distillation, reflux is essentially a purification step (aka rectification) where the liquid is vaporized and condenses within itself. The rectification is closely related to the volatility of the components of the matrix. Compounds with lower volatility (water) will easily participate in reflux, thus enriching compounds with higher volatility (ethanol) in the alcohol stream. In general, this creates a lighter flavor profile with a higher alcohol content.

In batch distillation, there are several design elements that can impact the reflux level, such as: shoulders, neck, lyne’s arm, and the pot itself.

The design of the pots is inherently essential for practical reasons; but, from the point of view of the rectification, the level of filling of the pot and the materials of construction stand out in importance. The level of filling has an impact on the quantity of surface which can participate in the heat exchange with the environment; higher fill levels decrease the heat transfer surface. Heat transfer is also impacted by building materials; copper is common due to its excellent heat transfer properties. This exchange facilitates the reflux on the walls of the pot, the neck and the shoulders of the still.

So shape, curvature, width, and height can all have an impact. Above the pot and the shoulders is a tapered section called the neck. Common designs include plain, ball, lantern, and tray inserts (in order of grinding). Pot stills with trays in their necks are called hybrid stills or batch straighteners because the trays are key design elements of continuous distillation.

Lyne’s arm connects the neck to the condenser. Although the main function of the lyne arm is to direct the vapors to the condenser, it also provides an opportunity for condensation or reflux. Depending on the angle of the lyne (aka gooseneck) arm connection, there may be an impact on the flavor profile with obtuse angles providing more backflow and acute angles providing the least.

Other rectification design elements exist, such as dephlegmators and purifiers. Although they are not always essential, they provide another opportunity to create a unique spirit. Typically, these devices use cooling water to condense the passing vapors. Dephlegmators are located in the neck of a hybrid still and the condensed liquid naturally flows back down. Installed in a downward sloping lyne arm, the purifiers require additional piping to route the condensed liquid to the pot.

Although these partial condensers may be optional, complete condensation of the vapor is required to make the final alcohol.

Reflux considerations (image via Liz Rhoades)

Condensation and collection

Condensation of vapor to liquid (distillate) is usually done by one of two types of condensers: shell and tube or worm and tube. Before the advent of the modern shell and tube condenser, augers and vessels were state of the art. All the steam is passed through a coiled pipe (normally copper) into a cooling water tank and the condensed steam is collected.

While not as effective as their modern counterparts, they do have some advantages in providing potentially richer and stronger (i.e. meaty) flavor profiles. Shell and tube condensers consist of tubes inside a metal cylinder (shell) filled with water; the vapor enters the tubes and condenses on the water-cooled surface. Once condensed, the still embarks on the most critical stages of batch distillation: cuts and collection.

Collection is usually done through an intermediate glass box on the way to the collection container (s), called Spirit Safe. This is the distiller’s first opportunity to evaluate and analyze the newly condensed distillate, usually by measuring the alcohol with a hydrometer in the spirits. With this information, the distiller can determine when to proceed to collecting buds, hearts or tails or when to complete the distillation completely.

Samples can also be taken for external evaluations, such as evaluation of aromatic properties. Sensory level and alcohol level are often used to determine cut-off points, although they can also be time-based. As with most still design elements, there are variations; Either way, a certain version of a spirit is an integral part of the cutting process, as the cutting process plays a vital role in the final quality of the distillate..

Conclusion

Pot still to pot still, a “Sherry Butt load” of variations can exist. While not entirely responsible for the diversity within the whisk (e) y space or other categories of distilled spirits, these differences can play an important role. Personally, it’s exciting as a distiller and a consumer to reflect on and appreciate this.

Even though there are some anatomical elements that are essential, such as safety features, heat, and the potty itself, the design can still be quite dynamic. From frustoconical configurations to the dephlegmator, the distiller has many options to consider as the still will inevitably become the heart and soul of the distillery (bumps optional).

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