What Makes It Through the Still: The Hidden Chemistry of Distillation

Distillers are often seen as artists—but underneath the surface, they’re also chemists.

While the goal of distillation is typically to extract ethanol, the real magic lies in shaping what else survives the journey through the still. Flavor-active compounds, volatile esters, heavier alcohols, and even sulfur compounds all play a role in defining a spirit’s character.

Thanks to the work of whisky flavour explorer John Angus, we now have a powerful framework to understand how four core elements—still shape, boiling point, reflux, and copper—act as filters to sculpt flavor during distillation.

Let’s explore how this hidden layer of chemistry determines what ends up in the glass.

1. Still Design: The First Flavor Filter

A still’s design isn’t just aesthetic—it’s functional. Everything from neck height to lyne arm angle plays a role in how vapors behave.

Key Concepts:

• Tall necks + upward lyne arms encourage reflux, which sends heavier vapors back down, refining the spirit.

• Short necks + downward angles allow more heavy compounds through, resulting in a weightier, oilier distillate.

• Wider necks or open-top stills increase contact with copper (more on that later), affecting sulfur and ester retention.

Your still shape is your first flavor decision.

2. Boiling Points: Timing is Everything

Different compounds boil and vaporize at different temperatures. As the wash is heated, the lightest molecules rise first.

Distillation Cuts:

• Heads (Foreshots) – Highly volatile compounds like acetaldehyde and methanol (20–80°C). These are usually discarded.

• Hearts – Where the most desirable compounds live: ethanol, fruity esters like isoamyl and hexyl acetate (80–150°C).

• Tails (Feints) – Higher boiling point alcohols like 1-hexanol and fatty acids like hexanoic acid (150–200°C+). These can add depth but often bring funk, sulfur, or bitterness.

The timing of your cuts defines the character of your final spirit—cut too early and you lose nuance; too late and the profile becomes heavy, even off-putting.

3. Reflux: Nature’s Filter Inside the Still

Reflux is the process where rising vapor condenses and falls back down, giving heavier elements another chance to be stripped out.

What Influences Reflux:

• Still shape (as mentioned)

• Cooling system efficiency

• Collection rate (slow = more reflux)

• Packing or trays (in column stills)

Outcome:

• More reflux = cleaner, lighter spirit

• Less reflux = oilier, richer spirit

Reflux is where balance begins. It gives distillers control over clarity versus complexity.

4. The Power of Copper: The Final Polish

Copper isn’t just a historical material—it’s a functional filter.

Key Functions of Copper:

• Removes sulfur compounds like mercaptans, which cause off-notes (rubber, cabbage).

• Enhances esters by allowing fruity, floral volatiles to shine.

• Buffers acidity and pH by reacting with undesirable compounds.

• Feeds esterification reactions, aiding the bonding of acids and alcohols into flavorful esters like ethyl acetate or isoamyl acetate.

The more surface area contact with copper, the brighter and smoother the spirit.

Want heavier flavor? Use stainless steel or reduce copper exposure. Want elegance and polish? Let copper do its job.

The Interplay: Change One, Change Everything

Each of these four filters is a lever. But they don’t work in isolation.

A taller still with lots of reflux might require later cut points. A short-necked pot still with minimal copper may need a slower run or tighter tails cut.

That’s the art of distilling—each decision influences the next.

As John Angus summarizes:

“It’s not just about collecting ethanol. It’s about shaping what survives the journey into the glass. Change just one variable, and the whole thing shifts.”

About the Illustrator

This visual breakdown and chemical insight are the work of John Angus, a leading voice in whisky education and flavor chemistry. His illustrations and commentary are used in training programs, distillery workshops, and academic settings worldwide.

Brindiamo is proud to feature John’s work with permission. If you’d like to explore licensing, visit his LinkedIn page here.