Friday, January 18, 2019

The Physics of Batch Column Stills and Bubble Plates

Until recently the graceful pot stills of Scotland were the most familiar images people had when you talk about distilling. Now batch column stills, also known as hybrid, reflux, or Lomond stills, common in the eau de vie and craft distilling industries, are far more recognizable than they used to be. These occupy an important middle ground between simple pot and more complex continuous stills, representing an evolution of the double retort pot still. In the simplest way of thinking about them, batch column stills are a way to create more refined spirits while using a smaller footprint by increasing the number of times that vapor is condensed back into liquid between the pot and the condenser.

New Deal Distillery's hybrid still
I've previous written about the physics of pot stills, which gives important background explaining concepts such as separation/resolution and reflux. Pot stills come in a bewildering array of shapes that are designed to influence reflux, but columns put all of that complexity inside far more plain-looking tubes. All of them operate by putting some kind of material in the path that the vapor travels from the pot to the condenser to create more opportunities for the vapor to condense and flow back towards the pot. The simplest method involves packing the column with small, high surface area items made of copper or a non-reactive material. In the same way that vapor condenses on the walls and flows back into the pot in a pot still, packing a column with material creates even more surface area for that process. Because the surface area is so high in a packed column, the vapor stream will also exchange material with the wetted surfaces in the column, further enriching the vapor stream with lower boiling constituents and depositing higher boiling constituents in the liquid. One of the significant challenges in setting up a packed column is ensuring that there is still enough void space for vapor and liquid to pass through the material without creating an unsafe amount of pressure. Another downside is that packed columns often have to be disassembled and emptied to clean the packing material thoroughly, which can be a significant challenge with larger columns. While these materials give a very high amount of reflux, care must be taken with the amount and type of packing material. A highly packed column may only be suitable for the production of neutral spirits because the product coming off the still will be almost flavorless. Using copper mesh also creates more opportunities for the metal to catalyze chemical reactions, which may be good for reducing sulfur compounds in the vapor, but can also lead to higher levels of acetaldehyde in general or the carcinogen urethane from fruit mashes with high amounts of cyanide in them.

The art of constructing hybrid stills is figuring out how to create a greater amount of reflux than a simple pot still while still producing flavorful spirits. This generally requires some kind of plate design, which has the advantages of letting distillers more precisely control their reflux ratio.

The simplest setup in this category is the sieve plate, which is just what it sounds like - a perforated plate, usually made from copper. The size of the plate and the ratio of holes to surface determine the amount of reflux each plate generates. Basic sieve plates have two significant advantages - first, they are simple to manufacture and thus cheap and second, they can be installed in the column on pivots that allow them to be turned 90º so that they create a minimal amount of reflux. This allows a distiller to tune the amount of reflux in the column for the type of spirit that they want to create, which is analogous to being able to change the shape and height of a pot still. This flexibility is especially important for craft distillers who want to produce multiple types of spirit on the same equipment. A larger multi-plate column can be fully engaged for making vodka, while most of the plates can be disengaged for more flavorful spirits like whiskey or brandy. Alternatively, creative plumbing can allow multiple columns to be used in series and selectively bypassed, so both a short and a taller column can be used for lighter spirits while the shorter column alone can be used for more flavorful spirits.

Sieve plates with sufficiently small holes operate with a layer of condensed liquid on top of them that is kept from falling back through the holes by vapor pressure. If the vapor pressure is not maintained at an adequate level liquid can 'weep' through the holes, reducing the efficiency of the plate. Some plate column stills have sufficiently high reflux ratios that liquid will collect on the plates passively, others require the plates to be preloaded with wash or water before the run, and many will use a dephlegmator, which is a partial condenser at the top of the column, to build up liquid on the plates. The plates will also need something called a downcomer (see diagram at right), which is a tube that allows liquid to drain from one plate to the plate below it. This pipe is built with a fixed or variable amount of height above the plate to ensure that the liquid level doesn't drop to zero. Similarly the lower end of each downcomer pipe is surrounded by a weir, which prevents vapor from traveling up the downcomer and bypassing the plates. The arrangement of the downcomers forces the liquid to flow across the plate from one side to the other, ensuring good contact between the vapor and the liquid as it proceeds back down to the pot. This setup means that vapor passing through each plate will exchange its heat with the liquid, depositing lower boiling compounds in the liquid phase and vaporizing higher boiling compounds to proceed upwards in the enriched vapor. In essence each plate becomes a small pot still, with the vaporization and condensation processes happening multiple times in miniature. This can be seen as an evolution of single- or double-retort pot stills (primarily found in rum distilleries) and thumpers (primarily used in bourbon distilleries) where the output of one pot still is passed through liquid in a subsequent pot still, then some of the liquid content of the pot is passed back to the previous still.


Bubble cap and valve plates are the next step up, meant to more effectively maintain the liquid level on the plate. While there is significant variation in design, all consist of small pipes with caps or valves on top of them. The liquid on the plate is prevented from passing through the pipe by the pressure on the cap or valve, while vapor can flow up and around to pass through into the liquid. This design allows the still to operate at a lower vapor flow rate than a simple sieve plate because the design reduces or eliminates the chance of weeping.

With all of this careful engineering, what's the point? There are any number of factors that can be pointed at, ranging from smaller footprints (no need for a huge pot still to produce light spirits when you can do the same thing with a more compact column), to efficiency (high reflux columns can be run harder than a pot still without loss of separation), to control and flexibility (pot stills only have two axes of control - heat input and condenser cooling water input). A classic example comes from the world of unaged fruit brandies or eau de vie, which were some of the first major users of batch column stills. This is because they found that the products from single pass distillation in batch columns were significantly different than double distillation in simple pots for certain types of fruit. For instance, one study found that while total ester levels were higher in pot distilled cider brandies, the levels of higher alcohols were elevated in the reflux column distillates.

The utility of batch column stills is even more clear for the craft distilling industry. They are faced by an array of challenges stemming from the huge amounts of capital that are needed to start a commercially viable distillery. Batch column stills present solutions to many of those problems. While they are more expensive than simple pot stills, they are far less expensive than continuous stills or multiple pot stills. They can be configured to produce an array of different spirits from the same system, allowing a new distillery to make lighter unaged spirits that can be sold immediately as well as heavier spirits that are designed for aging in casks. The increased efficiency and smaller footprint both help to save money and maximize the utilization of valuable space, especially for distilleries located in urban areas with higher real estate prices. Last, but not least, they allow the dynamics of distillation runs to be radically altered in comparison to pot stills.

Diagram of New Deal Distillery's hybrid still
The combination of a dephlegmator and a plate column allows for almost unprecedented control over how a distillation run proceeds. With a simple pot still, the only choices available are how to input heat into the pot, the rate that cooling water flows into the condenser, and where the cuts are made. While these tools are obviously sufficient to create some of the best spirits on earth, they require a lot of trial and error to perfect. With a batch column still equipped with a multi-plate column and a dephlegmator, a skilled operator can do something completely impossible with a simple pot still - establish, albeit temporarily, equilibrium. With 100% reflux the pot and column effectively become a closed system. The components of the heads will be compressed into the vapor phase near the top of the column, while the tails are all firmly in the pot. By reducing the flow of the dephlegmator a bit, the heads will leave the column in a comparatively small volume with very little alcohol. With further reduction in dephlemator flow the hearts will then come in behind at a constant ABV, unlike the steadily declining ABV of the hearts fraction from a pot still. Further tweaks will also compress the tails fraction so that very little of the fusel oils contaminate the hearts. This allows the creation of a very clean hearts fraction that can be bottled directly or that needs very little aging to round off its remaining rough edges.

An example of this flexibility is Westland Distillery in Seattle. Though they run a standard double distillation process for the majority of their spirit, their wash still is a batch column still. It is primarily used as a pot still with the dephlegmator turned off and open drains (see below) that empty the plates back into the pot, giving a greater amount of copper contact but with essentially pot still characteristics. Its full capacity is used to redistill the combined heads and tails from previous runs on the spirit still, with the dephlegmator fully engaged and the drains closed to keep the plates flooded to compresses the heads, then slowly reducing the cold water feed into the dephlegmator to extract a cleaner set of hearts, albeit with different character from their standard double distilled spirit.

Westland's wash still - see plate drains on the left side of column
There has been a long-running debate within the spirits community about whether batch column stills count as pot stills. On the one hand, they both operate in batch mode, which influences how the spirit is shaped through cuts. On the other hand, a fully equipped hybrid still with a column and dephlegmator can manipulate the process of distillation in ways that are simply impossible with pot stills, producing very different sorts of spirits. Being able to produce clean, high-proof spirit in a single pass is fundamentally different than simple pot stills, which is demonstrated by their use in the fruit brandy industry. At the same time, the line between the two is blurred by double retort pot stills, which are widely acknowledged to be pot stills, but share characteristics with batch column stills utilizing only a few cross-flow plates. While there is a hard break between batch columns and continuous stills, what the debate really comes down to is mystique - are people willing to pay more for pot still spirits because they expect a certain level of quality and character? I would argue that batch columns can produce spirits of equal quality, as long as the distiller is skilled enough to use their equipment to its maximum potential. If the reputation of batch columns has become tarnished, that is because of the people using them, not because of the technology itself.

Wednesday, January 16, 2019

Whisky Review: Balvenie 12 Year Doublewood 40% vs. 43%

Balvenie is the crown jewel of William Grant & Sons, outshining the more pedestrian Glenfiddich and nearly unknown Kininvie and Aisla Bay. Balvenie is the 'classier' single malt, with a more boutique market position and a price point to match. Justifying some of the extra expense, it maintains its own floor maltings, which provide somewhere around 10-15% of their requirements.

The 12 Year Doublewood is currently Balvenie's entry-level single malt, which is initially aged in ex-bourbon casks, then transferred to sherry casks for a few months before the casks are blended together and proofed down for bottling. There are two versions, one at 40% and one at 43%, which made me wonder if they are significantly different.

Doublewood 40%

Nose: a solid dose of American oak, caramel, graham crackers, light sherry and malt, grassy, cinnamon. After adding a few drops of water the malt notes become strong while the sherry and oak are softer and something a bit soapy comes out.

Taste: bittersweet sherry and oak up front, honey, vanilla, mint, and malt in the background throughout, sliding into a mellow and slightly muted finish. After dilution the sherry is slightly amplified over the oak, but it's initially somewhat thin overall - only gains strength with time in the glass.

Finish: sherry and oak residue, honey, malt, vanilla, mint

While this is a perfectly acceptable whisky, it's only a half step up from its sibling Glenfiddich 12 Year and roughly comparable with Glenfiddich 15 Year Solera. In no small part I think that's the result of the low bottling strength, which lets down what is already a fairly delicate malt. It could be more robust and interesting at 46% without chill filtration, but we're unlikely to see that as long as sales remain high.





Doublewood 43%

Nose: balanced malt, sherry, vanilla, and oak, honey, grassy/herbal/floral. After adding a few drops of water the oak becomes less prominent and the malt is softer, with more honey and grassy notes.

Taste: balanced malt and sherry throughout with moderately tannic oak in the background, some green/grassy notes around the middle, more robust and dank bittersweet sherry going into the finish. After dilution it becomes sweeter and less tannic, with brighter sherry notes and more malt throughout.

Finish: oak tannins, sherry residue, clean malt

While the structure is similar between this and the 40% version, the extra 3% alcohol (despite the fact that some of the mini evaporated) makes a significant difference. The aromas and flavors are far more robust and make it far more drinkable. It's possible that this is also due to the fact that I bought the mini in late 2011, when Balvenie had deeper stocks and was able to use longer sherry finishes. While I still prefer the balance of Founder's Reserve with its better-integrated sherry and reduced oak, time has made this version of Doublewood seem more competent in comparison to other entry-level malts available at the moment.

Monday, January 14, 2019

Balvenie Blowout

Balvenie occupies a very particular place in the whisky world, simultaneously appealing to geek sensibilities with their regular experimental releases and craft approach to production, while rarely creating anything so challenging that it doesn't have relatively broad appeal so that the legions of Glenfiddich drinkers have somewhere to step up when they want something a bit fancier. They get a lot of cred for being one of the few major distilleries to still use their own floor maltings for part of their requirements, which also adds a picturesque flourish to their extremely popular distillery tours as well as (presumably) something to the final product.

From Balvenie Distillery
Their ambiguous position is amplified by the fact that their prices tend to sit roughly a slot higher than most of their competition, e.g. their 15 year olds tend to go for 17-18 year old prices and their 17 year olds tend to go for 20-21 year old prices. This begs the eternal question of whether they're delivering value, especially when you consider that most of their releases are bottled at 40-43% with chill filtration and possibly coloring.

Over the years I've amassed a fairly large number of Balvenie samples, from a miniature set that was sold in the early-2010s to samples of new and old releases ranging from 12 to 21 years old. While there are a few oddballs, I've mostly been able to present them in pairs that look at particular styles within their lineup. Overall my goal is to try to get a better sense of what the distillery has to offer and whether my opinions have changed at all over the last six years.

Friday, January 11, 2019

Whisky Review: Longrow Peated

Much like Hazelburn, Longrow has had an unstable lineup in recent years. There was a period when it had a full range consisting of the NAS CV, plus aged dated 10, 14, and 18 Year expressions. More recently that has collapsed down to the NAS Peated expression, the annual wine cask Red releases, and the older 18 Year, with nothing holding down the middle of the range. Hopefully this is a temporary state of affairs as the distillery rebuilds stocks, but only time will tell.

This whisky was aged entirely in ex-bourbon casks, then bottled at 46% without coloring or chill filtration.

I purchased this sample from Whiskysite.nl

From Springbank Distillery
Longrow Peated

Nose: minty toothpaste, fresh malt, mellow peat and hay, leathery oak, buttery. After adding a few drops of water it becomes softer and the peat becomes ashier, but the overall profile stays the same.

Taste: lots of bourbon cask sweetness up front, turning bittersweet with mild oak, peat, and some vaguely fruity top notes from the middle back. After dilution the peat gets stronger and moves forward but remains fairly mellow overall, while the sweetness gains a floral edge.

Finish: light balanced peat, oak, and malt sweetness

I first tried this whisky at a tasting event a few years ago, not long after it was first released. That was also not too long after I had tried the CV expression and found it to be one of my favorite Longrows. So I was extremely disappointed to find that the newer Peated version just seemed tepid in comparison. But I chalked that up to it being the first version and hoped that it would improve in subsequent releases.

So I'm very sad to say that it still doesn't do anything for me. This has nothing of the waves of vegetal peat and TCP I found in the CV, leaving a relatively mild whisky with little to distinguish it. There doesn't even seem to be that much peat, belying both its name and the fact that the components are presumably not particularly old.

This is rather unfortunate as the eye-watering price tag of Longrow 18 Year means that this is likely to be the first and possibly only introduction people get to Springbank's heavily peated malt. As is, I'm glad to have a few other Longrows tucked away to keep me company, because this one will not be joining them.

Wednesday, January 9, 2019

Whisky Review: Springbank 10 Year (Orange Label)

I have had a rather mixed relationship with Springbank's 10 Year. Sometimes it was too dirty (see, the previous iteration), other times it was too sweet (see, the iteration before that). They have a delicate balancing act to perform, since the distillery character can become overbearing without the right application of time and casks. But I keep returning to it because I know how good their whisky can be when it hits the mark.

This whisky is aged in a mix of bourbon (60%) and sherry (40%) casks, then bottled at 46% without coloring or chill filtration.

I purchased this sample from WhiskySite.nl

From Springbank Distillery
Springbank 10 Year (Orange Label)

Nose: classic Springbank dirty peat, pine, fresh malt, leather, light sherry, creamy vanilla, and a coastal undercurrent. After adding a few drops of water the dirty Springbank character gets more prominent, the other components retreat, and it gets drier and saltier overall.

Taste: sweet malt and sherry up front, cleaner malt with some peat-y dirtiness and creamy vanilla in the middle, more sherry and very mild oak at the back. After dilution the sherry gets more assertive throughout, the dirtiness resolves more clearly into peat, more vanilla comes out around the middle, the oak gets stronger at the back, and it comes off hotter going into the finish than it does undiluted.

Finish: moderate oak, sherry residue, and dirty peat

This appears to be closing in on the goldilocks point - the sherry is present without being overwhelming, the peat is a component without making it too dirty. While its price point is absolutely absurd locally ($81.95 as of this post), it's a much better deal if you're shopping elsewhere in the States or ordering from the EU. At $50 or less, I would be hard pressed to find many better single malts on the market these days if you want that grungy but not overly peaty character that Campbeltown provides.

Monday, January 7, 2019

Whisky Review: Hazelburn 10 Year

Hazelburn has been one of Springbank's expressions without a super stable lineup. For some time there were an NAS CV expression, an 8 Year from a mix of bourbon and sherry cask, and 12 Year entirely from sherry casks. There has been a major revision since then with the CV disappearing along with the rest of that lineup, the 8 Year being replaced by this 10 Year, and the 12 Year being phased out in favor of an annual Sherry Wood release at cask strength.

This whisky was aged exclusively in ex-bourbon casks, then bottled at 46% without coloring or chill filtration.

I purchased this sample from Whiskysite.nl

Via Springbank Distillery
Hazelburn 10 Year

Nose: lots of fresh malt and corn, something sour/beer-y, vanilla, light fruit/berry esters, orange peel, very light oak. After adding a few drops of water it loses some of the sourness and becomes more integrated, the oak becomes musty, and some coastal character emerges.

Taste: sweet up front, but quickly joined by an overlay of sour malt through the middle, a smoother fade out at the back with caramel, something savory, and light oak. After dilution the sourness is reduced, more oak comes out to give it better balance and an almost sherried quality, there is some vague fruitiness in the background throughout, and a little coastal character comes out around the middle.

Finish: moderately sweet malt, sherried oak, a little sour, dunnage, savory fade out

I'm surprised to say it, but this was one whisky where I wish they had used more active casks. My favorite Hazelburns have been the ones with a significant amount of cask influence in tension with the spirit itself. Dilution helped to push it more in the direction I wanted, but it lost some of the intensity at the same time. Dilution helped to push it more in the direction I wanted, but it lost some of the intensity at the same time. While this has potential, it ultimately feels underdone and raw at full strength to me. Not nearly as bad as the 8 Year Cask Strength, but closer to that or the CV than the Bourbon Single Cask I was hoping for. While this is a good effort, but it's making me thankful that I didn't buy a bottle blind.

Friday, January 4, 2019

Armagnac Review: Château de Pellehaut 28 Year 1989/2017 100% Ugni-Blanc

Not a whole lot to say about Pellehaut that I haven't already said. This is from an earlier era when they were primarily distilling ugni-blanc grapes as opposed to folle-blanche. This is another purchase from Astor Wines in NYC that is currently unavailable, though it seems like they've gotten multiple parcels of 1989 vintage casks with progressively more recent bottling dates, so something similar may show up sooner or later.

This brandy was distilled from 100% ugni-blanc grapes in 1989, filled in a new oak cask, then bottled at 49.9% without coloring, chill filtration, or additives.

Château de Pellehaut 28 Year 1989/2017 100% Ugni-Blanc

Nose: lots of spicy oak, cedar, caramel/maple syrup, dried fruits, floral vanilla, dark chocolate, a little savory. After adding a few drops of water it gets softer and sweeter with more balanced oak, the maple syrup turns into honey, and the savory notes integrates with the wood.

Taste: balanced grape and cask sweetness up front, moderately tannic and spicy oak with dried fruit in the background beginning in the middle, turning bittersweet at the back with a little heat. After dilution it becomes sweeter throughout, the oak takes a more balanced back seat, and the grape notes pop more at the back.

Finish: long but fairly simple - spicy oak tannins, background grape sweetness, and a savory fade out

There are a lot of similarities between this and the slightly younger folle-blanche cask I reviewed earlier. I think the balance it tipping towards the oak here, so it reads as a little less expressive to me. It really makes me wonder what the even older 1979 vintage bottle I have will be like, but we'll have to find out later.

Wednesday, January 2, 2019

Armagnac Review: Château de Pellehaut 23 Year 1994/2017 100% Folle-Blanche

There are not many big players in the American armagnac market, but Astor Wines in New York has put themselves at the center of it, alongside K&L Wines on the other coast. They regularly have a significant selection of brandies and bring in their own cask picks with some regularity. Unfortunately this particular cask has sold out, but there are always new picks available and their quality has reportedly been pretty consistent.

This brandy was distilled from 100% folle-blanche grapes in 1994, filled into a new oak cask, then bottled in 2017 at 48.2% without coloring, chill filtration, or additives.

Château de Pellehaut 23 Year 1994/2017 100% Folle-Blanche

Nose: strong oak and maple syrup, sweet grapes, honey, nougat, vanilla, nutmeg, allspice, fresh hay. After adding a few drops of water it becomes softer but more muddled, with less well-defined oak, but more unripe fruit/grape notes come out along with something dry and almost grainy

Taste: strong barrel and grape sweetness up front, backed by a significant amount of oak that becomes syrupy and more tannic with something savory in the background as it moves towards the back, and a bump of fruity esters and orange peel around the middle. After dilution the sweetness remains strong, the oak fades a bit and integrates into the whole, and the savory note at the back turns into a slightly acidic citrus/fruit note alongside gentler tannins.

Finish: rather long - oak tannins, syrupy grape sweetness, spicy/acidic prickles, a savory fade out

This one took me a while to wrap my head around it. It definitely requires some time in the glass to open up and I needed multiple tastings before I could work my way through the oak to get at the other components. With that said, I actually found this more in balance than some of the younger casks I tried, largely because the sweetness has expanded to a point where it is not overwhelmed by the more bitter tannins. My only complaint is that I wish the savory character I found in the finish had been more assertive as I feel like that would have made for a more interesting and complex experience, but it's a fairly small quibble. Water definitely helps to soften the oak, but you have to like the acidic fruit character that pops out. Overall this was a quality cask and a good pick.