High Fidelity Gin Distilling / Perceptual puzzles / Musings

Recently I’ve helped a few people start the journey of developing a gin. All I’ve really done is give people stuff to read so they were up on all the published literature. Sadly, gin has the most incomplete of all the distilling literature and it takes a lot of seeing for yourself to really get anywhere with it. One of the incomplete parts of the gin literature is how you make cuts, why you make them, and then what do you do with the cut fractions. Can they be recycled like in other spirits?

Gin is primarily made from neutral spirit on stills that we assume are free of fusel oils from the previous distillations of other types of spirits (remember the demisting test?). For atmospheric distillation (because gins are often distilled at vacuum or just partial vacuum), the heads cut is to separate unwanted terpenes which can have solubility issues when cut to bottling strength among other issues.

Terpenes are a very broad category of flavor compounds with differing volatilities and differing ethanol/water solubilities. I haven’t really figured them out to be honest. Think of them as what makes an expressed lemon peel so fresh, zesty, and angular. I think we could compare terpenes encountered in gin distillation to the esters and say some are more noble than others. Like the esters, many terpenes are formed (or transformed) in the still and more form at higher temperatures than lower which is why in both cases vacuum distillation produces less of each.

Terpenes are also more soluble in ethanol than they are in water which is why a Lemoncello has to be above a certain alcohol content to not cloud, the same with an Absinthe which louches when water is added, and the same with the first fractions of a gin when cut with water. But then at a sensory level, why do we want them in a lemoncello but not in a gin?

Strange sensory stuff happens with terpenes, perhaps just the generic ones, where they raise the threshold of perception of an essential oil therefore somewhat masking it. Sadly, I can’t find the why of this explained anywhere. All you really just see in perfume or flavoring literature is the rule of thumb that essential oils should undergo terpene separation to reduced the usage rate. But consider the Lemoncello, non removal of terpenes is not always a flaw, immediately we find a context where it is a significant feature.

Terpeneless and concentrated citrus oils from which only a part of the terpenes have been removed are widely used as flavoring materials as they have improved stability and a longer shelf life, a lower usage rate, and improved solubility making them of particular value in the flavoring of soft drinks and liqueurs. -Flavor Chemistry And Technology, Second Edition by Gary Reineccius.

This usage rate claim is wildly interesting and a surprise that it isn’t investigated further anywhere that I can find. Does some strange perceptual phenomenon happen when terpenes are removed, and is mastering this critical to creating high fidelity gins?

Cointreau was revealed to use a centrifuge in their production process but was very cryptic about why exactly they used it and Joseph Merory shared a wildly intricate recipe for a triple-sec that had multiple stages of terpene removal but no detailed explanation why.

What I’m wondering is if any of the heads fractions of gin distillations can be process by centrifuge for ignoble terpene removal then reintroduced into the hearts fraction to maximize fidelity because undesirable terpenes and desirable volatile oils are likely to overlap. Cointreau does staggering volumes and uses a continuous centrifuge, but batch style blood bank centrifuges are ubiquitous in culinary these days and the heads fraction of a gin distillation might practically be processed in one. But are any sophisticated producers doing this? It seems like the big guys are successfully private enough about their ways that they could be doing tons of things we don’t yet know about.

Hopefully I’ll be in a position to investigate this first hand soon. I do have a gorgeous three liter centrifuge ready to play with the fractions.

The other idea I’ve been curious about lately is how to teach the making of cuts by providing references from industry leaders and how this might be applied to working on the ultra small scale. When cuts are made to a distillation run of fermented spirit we are primarily concerned with tracking basic congeners like ethyl acetate, acetaldehyde and then fusel oil. We want these congeners as close to the recognition threshold as possible without going over. If they are over they will stick out and become a flaw (aka a regret or missed opportunity), but if they are just below they will support and bridge other aromas.

But this threshold line is for the overall spirit diluted with water and finished for the consumer. When we make the cut we are experiencing these congeners bunched up and over the recognition threshold so it can be tricky for new distillers to navigate. They don’t yet have the opportunity to see how things turn out down the road. Or what if they are making one offs and there isn’t much down the road? We need ways to trace references from a completed product back to when congeners are coming across the still.

Can we create references from the proliferation of white dogs on the market? The unaged white whiskeys could be taken and broken up in a vacuum still into segments. The critical segments would be at the beginning and the end where major generic congeners would be bunched up back over the recognition threshold. This would give new distillers targets to shoot for based on the decisions of major commercial producers.

What else am I missing?

Apparently I’m not the first person to use fidelity in this context and a helpful patent from Pepsi does the same. The patent is titled: Increasing the Terpene Compounds in Liquids and gives a nice background on the challenges. Here I’ll extract some choice passages:

Consumers also demand fidelity of flavor in soft drinks and other liquids.
[…]
The water-insoluble compounds in flavors typically make a significant contribution to the perception of flavor as a complete, true, faithful representation of the flavor. As the skilled practitioner recognizes, the water-insoluble compounds often introduce haze, cloud, precipitation, or a phase separation in aqueous liquids, or may form a ring on the beverage container. These phenomena may cause consumers not to accept the liquid because these phenomena often are taken as an indication that the liquid is unfit for consumption, or that the beverage has spoiled.
[…]
Removal of water-insoluble components from flavoring compositions, referred to as “extraction” or “washing” in the trade, typically provides an incomplete flavor. Thus, even though the liquid may not be hazed or cloudy, the product is rejected because the flavor does not mimic fruit flavor found in nature. For example, lemonade that does not contain an appropriate concentration of water-insoluble compounds tastes objectionably ‘watered down,’ or candy-like as compared to fresh squeezed fruit.
[…]
The inventors have discovered that terpene compounds are solubilized by addition of flavor compounds more polar than the terpene compound. The inventors have discovered that solubiiizing the terpene compounds enables a higher concentration of terpene compounds in aqueous solution. Therefore, transparent liquids can be made with a flavor that reproduces the intended flavor more faithfully than known flavor compositions that have lower concentrations of terpene compounds.
[…]
The skilled practitioner recognizes that it is possible to increase the concentration of terpene compounds in a composition by increasing surfactant concentration. However, the skilled practitioner also recognizes high surfactant concentration may lead to beverage formulation difficulties, including adverse flavor effects, high cost, excessive foaming, and the possibility that regulatory limits would be exceeded at a surfactant concentration required to achieve the desired concentration of terpene compounds.
[end quote]

So the strange thing is that the information here works against the earlier ideas of fidelity. Many people have the idea that ethanol is a powerful enough solvent, but various surfactants are included in the likes of Angostura bitters, Fee brothers bitters, and even certain gin line extensions like Tanqueray Rangpur. Apparently they do it for fidelity. And even in the products that Pepsi makes, this idea of fidelity might trump lowering of the usage rate mentioned above when terpenes are removed which could be economically very significant.

So where are we now? Terpene removal simultaneously increases and decreases fidelity?

In the world of alcohol and even perfume do we want fidelity and the faithful reproduction of an orange peel or do we just want raw, extraordinary, attention sensations like I’ve mused about before? Maybe its a matter of metaphor? The terpene removed gin doesn’t exactly have fidelity which would make it ordinary but rather it has some sort of contrast enhancement trick with an extraordinary clarity and sharpness not found in the natural world. Perhaps its like applying a hipstamatic filter of sorts.

Some times we get nostalgic and we want high fidelity Sorrento lemoncello because that is rare and extraordinary relative to other lemon experiences while other times we want that sharpness and subtle contrast enhancement of terpene reduced gins because that is extraordinary relative to ubiquitous high fidelity botanical experiences in your unabstracted every day lives. Gin, because of its manipulation is like watching David Lynch give the noir treatment to wholesome rural American in The Straight Story. The use of light and contrast enhancement lifts it all up to be subtly, subversively, more attentional; realer than real.