During my recent visit to Maison Ferrand (home of Cognac Ferrand and Plantation Rum) I posted a picture on Facebook that seemed innocuous enough. The caption read: “If you’re going to drink a cask-strength, 18 year Long Pond marque, the ITP (280 g/hL AA) is highly recommend. Even Mrs. Wonk loved it.”

A few minutes later, someone extremely knowledgeable about the rum industry posted a comment that caught me completely off-guard. The gist of the comment: Long Pond’s ITP marque is known to be in the 90-120 g/hL AA range. How can it be 277 g/hL AA?

I immediately conferred with Benjamin Galais, Maison Ferrand’s technical director, and Nicolas Malfondet, Maison Ferrand’s director of research and development. Both were graciously spending the afternoon with me, going over their findings from laboratory analysis on many different rums.

Benjamin disappeared for a moment and reappeared with several sheets of paper – detailed analysis of several different Long Pond ITP samples of different ages, all performed by Laboratoire Cognac Oenologie. First and foremost, the page with the 18 year Long Pond ITP did indeed say 227.4 g/hL AA. But it was the data on the remaining pages that lead me down a path of enlightenment about rum chemistry that even most experts don’t fully grasp.

If you’re deep enough into rum to know things such as the difference between tropical and continental aging, what I’ll explain here will knock your socks off. And if you’re confused by the above chemistry mumbo-jumbo, take heart! Let’s start from the beginning– soon it will all make sense.

Rum Marques

Much like bakeries make many styles of breads, distilleries create many types of rum. Some batches may have very light, delicate flavors, while other batches might target an intensely strong and pungent style. From the types of molasses and yeasts used to the temperature and fermentation time, and continuing on to distillation choices (pot vs. column, when “cuts” are made, etc.) a distillery can craft any number of different flavor profiles.

Each particular set of choices a distillery makes constitutes a recipe, just like baking. And this is all prior to any consideration of what happens during barrel aging. But for the purpose of this explanation, let’s focus on the rum’s recipe only up to and including distillation.

In rum terminology, the rum resulting from each particular recipe is known as a marque. You may also see it referred to as a mark, but they’re the same concept. I prefer marque, so will use it here.

In practice, every distillery has a set of marques–recipes they uses over and over, with the expectation that each batch will be similar in flavor profile to prior and subsequent batches of the same marque. Remember, we’re only talking about freshly distilled rum here, not aged rum.

Because of the expected continuity between batches of the same marque, they’re extremely useful to rum blenders. Their task is to create a consistent flavor profile for a blend, year after year. Naturally, they create recipes for each blend: This many liters of marque A, this many liters of marque B, and so forth. Great examples of blended rums made from several marques (from several countries!) include Banks 5 Island, Denizen Merchant’s Reserve, and Plantation O.F.T.D. Overproof.

Rums such as the above have been around for many years, and countless blended batches have been made. An expert blender often tweaks each batch of blended rum in small ways to main overall flavor continuity, but the basic set of component rums in a blend is usually fixed. That is, until a particular component marque becomes unavailable. The blender’s job then is to figure out replacement marques to maintain the blend’s profile.

Jamaica in particular is famous for its rum marques. In the dusty past, there were no distillery driven brands, like Appleton Estate is today. Rather, the Jamaican countryside had dozens of small distilleries pumping out rum for bulk sale to blenders and merchant bottlers. The challenge of many small distilleries all selling in bulk is that every distillery’s output is different from the others. For blenders of these bulk rums, such as E&A Scheer, some basic expectation of flavor intensity and profile was needed.

Eventually, the numerous Jamaican distilleries banded together into a “spirits pool” and agreed on a small set of national marques. The key differentiator between each marque is the measured ester levels–or in less geeky terms, how strongly flavored the rum is. In general, the higher the ester level, the more flavorful the rum. Confused about esters? Let’s take a quick look.

Esters – The Flavor Maker

Esters are a specific category of organic compounds that provide a flavor sensation when you smell or taste them. There are many different types of esters, each providing an aroma, like apple, pineapple, butter, mint, and so forth. Chemically speaking, ester molecules form when an acid joins up with an alcohol. There are both many types of acids (acetic, butyric, formic, etc.) and many types of alcohols (ethanol, methanol, isopropyl, etc.); the most important thing to understand here is that every spirit contains hundreds of different esters.

Each unique pairing of an alcohol with an acid creates a unique ester. The most common ester, ethyl acetate, forms when ethanol (the alcohol we drink) combines with acetic acid, better known as vinegar. (See this post for a much deeper dive on this topic.)

Esters can form at many points during the spirits-making process–anywhere alcohols and acids coexist. The fermentation process, where yeast converts sugars into ethanol and other alcohols, is a particularly fortuitous place for ester creation. However, they can also form during distillation, as well as in the barrel.

Since ethyl acetate is by far the most common ester found in distilled spirits, a measurement of its concentration was once used as a shorthand for how intensely flavored the rum was. A rum with more flavor, i.e. higher ester levels, commanded a higher price. In common usage, the ester level of a Jamaican rum is considered the same thing as its ethyl acetate level.

Be aware though: Intensity and flavor profile are completely unrelated. Two rums can taste completely different but have similar levels of ethyl acetate. It’s the additional esters, acids, and organic compounds that create the differences in flavor.

The commonly used measurement for esters is grams per hectoliter. This is typically written as g/hL AA, or grams per hectoliter of absolute alcohol. For example, an ethyl acetate level of 1 g/hL AA means there’s one gram of ethyl acetate in each hectoliter of spirit. (Any water in the spirit is ignored in this measurement.) A hectoliter is about 26 U.S. gallons, so when you compare one gram (0.03 ounces) of ethyl acetate to 26 gallons of ethanol, it’s clear that esters are an extremely small part of a spirit but impart a huge amount of flavor.

National Marques

Previously I mentioned the national marques once used by all Jamaican distilleries. At some point in the very distant past, the Jamaican spirits producers established the following marque names and ester ranges:

Common Clean (80-150 g/hL AA)

Plummer (150-200 g/hL AA)

Wedderburn (200-300 g/hL AA)

Continental (700-1600 g/hL AA)

If I was a betting man, I’d wager that the vast majority of today’s rum aficionados only know two of these marques: Plummer and Wedderburn, because they’re cited on the Smith & Cross label. Nothing wrong with that! Smith & Cross is a fine study aid when studying up on marques.

The Continental marque’s name warrants explanation. Briefly put, the highest ester Jamaican rums weren’t (and still aren’t) intended for general consumption in their pure form. Rather, they’re usually treated as concentrated flavor, used for blending with lighter rums.

The highest ester Jamaican rums took the high ester concept to an extreme in the early 1900s. Germany had imposed a heavy tax burden on imported spirits. To minimize their taxes, enterprising German merchants imported small quantities of super-high ester rums and blended them with locally made neutral spirit. In essence, the super funky Jamaican rums were used as rum concentrate. Google for rum verschnitt if you’re curious.

While these national marques were easy to remember and created consistent pricing for rum of a certain quality (e.g. Plummer), today’s reality is that they’re an anachronism. Almost no one in the rum trade buys or sells Plummer rum. Rather, each distillery defines its own unique marques. For the Long Pond distillery, here are the marques listed in my Jamaican Rum Marques Roundup Page:

CRV (0-20 g/hL AA)

CQV (20-50 g/hL AA)

LRM (50-90 g/hL AA)

ITP/LSO (90-120 g/hL AA)

HJC/LIB (120-150 g/hL AA)

IRW/VRW (150-250 g/hL AA)

HHHS/OCLP (250-400 g/hL AA)

LPS (400-550 g/hL AA)

STC^E (550-700 g/hL AA)

TECA (1200-1300 g/hL AA)

TECB (1300-1400 g/hL AA)

TECC (1500-1600 g/hL AA)

You’re probably wondering what all those letters mean. So are many Jamaican rum geeks. Deciphering them isn’t easy, but a few guesses can be made. For example, “LP” is likely Long Pond. And VRW is Vale Royale Wedderburn. Figuring out what all those letters stand for is an amusing parlor game for the Jamaican rum obsessed.

Solving the Mystery

So now, let’s return to the mystery of the photo I posted. The sample bottle said ITP, which is an ester range of 90-120 g/hL AA in the above list. However, the laboratory analysis showed the ethyl acetate measurement at 277 g/hL AA, which puts it firmly in the HHHS marque range. So which is it: ITP or HHHS?

The answer illuminates the magic of cask aging. As I’ve said before, the purpose of cask aging isn’t to make your spirit taste like wood or make it “smooth.” The purpose of cask aging is to allow additional organic chemistry processes to play out in slow motion over a long period of time.

When this ITP rum was distilled 18 years ago, its ester level very likely measured between 90 and 120. Freshly distilled, it was unambiguously in the ITP range. However, eighteen years in a cask radically transformed the rum. When it first entered the cask, there was plenty of alcohol and plenty of acid in the rum. Over the fullness of time, some of those acid and alcohol molecules paired up to form esters.

In addition, because of the angel’s share, ethanol evaporates through the cask walls at a higher rate than the esters. This has the effect of increasing ester concentration. Put another way, the relative proportion of esters to the overall spirit increases, i.e. the g/hL AA measurement goes up.

Between ester formation and ethanol evaporation, this in-barrel esterification didn’t form just a few more esters. Rather, it tripled the ester level–from approximately 90 g/hL AA to 277 g/hL AA.

The fact that in-cask esterification can change ester levels so much creates a conundrum of sorts: What marque do you use to label the rum? The ester levels immediately after distillation or the ester levels when it’s sold? As best I’m aware, there are no regulations that address this question. However, we can ponder whether it makes more sense to assign a marque based on ester levels after distilling vs. after aging.

For starters, let’s dismiss the idea that marques and ester levels are exactly the same thing. An ester level is just one dimension of a marque. Let’s do a thought experiment to show why.

Let’s say Long Pond makes a batch of the ITP marque. The rum will have hundreds of organic compounds, making for a particular flavor profile. Now imagine the distillery makes a batch of TECA marque rum (1200 g/hL AA). That rum has ten times the amount of esters. But because of different mash recipes and fermentation times, the relative amounts of each ester are very different than in the ITP rum. If you put all the ester levels on a graph, they’d have a different “curve” when comparing the ITP and TECA rums.

Put another way, if you took the TECA rum and added enough pure ethanol to it to reduce its ethyl acetate level to match the ITP rum, it would still have a different taste. You can’t make a TECA marque rum taste like ITP rum just by adding ethanol to make the ethyl acetate levels match up.

For this reason, I contend that marques should be assigned to a rum based upon the ester levels immediately after distillation. That assigned marque should stay with the rum regardless of ester creation during aging. That’s exactly happened with these Long Pond samples.

The distinction between pre- and post-aging ester levels and marques has tripped up even the experts. A well-known independent bottler recently received TTB label approval for a Hampden Estate rum with an “LFCH” marque and an ester level of 231.3 g/hL AA. Per the Hampden Estate marque list, LFCH is 85-120 g/hL AA, which I verified with a Hampden Estate employee.

It seems clear this rum was distilled to LFCH marque ester levels, then subsequent aging brought the ester level up to 231 g/hL AA. Nothing amiss with that. However, the bottle’s back label says, “LFCH is a rare Hampden mark identifying a rum with 200-250 gr/hlpa esters.” That statement is at odds with what we know of Hampden Estate marques.

Science! Showing Our Work

Finally, let’s get a little geekier on this concept of in-barrel esterification. A single data point does not a theory make. Luckily, the Maison Ferrand people had four different ITP samples of different ages – unaged, nine years, 18 years, and 22 years, with a laboratory analysis for each.

As you can see from the chart below, the ethyl acetate, that is, the “esters”, more than triples after nine years, and, quadrupled after twenty-two years. If you were to use the national marques, this common clean rum eventually blew past the upper limits of the Wedderburn marque.

Marque / Age Ethyl Acetate measurement (g/hL AA) Volatile Substances (g/hL AA) ITP unaged 86.6 625.7 ITP 9 years 273.8 667.5 ITP 18 years 277.4 1028.5 ITP 22 years 386.9 1189.6

Before going any further, it must be stated that each of these ITP batches were distilled at different times, and unfortunately we don’t have the initial, pre-aging ester measurements of the now-aged batches. However, it’s fair to assume each batch was fairly similar immediately after distillation. Likewise, if you plot the ester levels against the age, it’s not a straight line. However, the trend is clearly toward the ester levels increasing over time, and in a substantial way.

Now that you’re an esters expert, let’s introduce one more measurement: Volatile substances, which are listed in the rightmost column. This measurement includes other organic compounds, in addition to esters–things like higher alcohols and aldehydes, which (believe it or not) are too geeky to get into here. Suffice it to say, volatile compounds also contribute to the flavor to a spirit. Volatile substances measurements are always higher than just the ethyl acetate measurement because they’re a superset.

Incidentally, the Martinique AOC specifies a minimum level of volatile substances. If you’re going to quote measurements like this when talking about a spirit, you have to be clear on exactly which measurement you’re speaking of. Make sure you’re comparing apples to apples!

In the interest of full disclosure, I’m not an organic chemist, although I do have a degree in physics. The data and discussion above isn’t anywhere close to a proper scientific study. A real study would have far more samples and controls. However, we have five data points that in combination illustrate a surprising aspect of the effects of cask aging—well worth some deep consideration with a snifter or two of aged Jamaican rum.

The making of spirits is both art and science. While the artistic elements make for fascinating stories and create a human connection to the spirit, the science is always below the surface, silently following the laws of nature. We’re still a long way from completely explaining all aspects of how flavors come to be and how we perceive them in scientific terms. The art of the spirits maker is figuring out how to corral the science we know into something that inspires our taste buds and souls.

I’d like to express my appreciation to the Maison Ferrand staff for sharing this laboratory data and an immense amount of their time with me and, in turn, permitting me to share it to illustrate this fascinating corner of the rum world.