The Congener Conundrum

The Congener Conundrum

One of the biggest misconceptions about congeners in rum is that quantity is a synonym of  diversity. Thus, all “heavy” rums (rums with high congener contents) are or should be  considered the same. The reality is that in the rum industry congeners are usually measured as the sum of heads, tails and acidity. Following this approach, a heads-strong and a tails-strong rum could have the same total congener content, but that does not mean both are equally good.

Heads-strong rums will have more aldehydes and esters, usually providing for sweeter, fruity complexity, while tails-strong rums usually have oilier, fuel-like attributes. I used the word  “usually” twice in the prior sentence as a launching pad to help me with my next point: many alcohol distilleries catering to both fuel-grade and food-grade markets have been changing their fermentation methods to use only one yeast strain for both purposes. The strain is typically one selected for its ability to produce ethanol and very little else (under proper fermentation conditions).

While these distilleries are able to produce “heavy” rums by congener quantity alone, the heads congeners in these rums are mostly limited to acetaldehyde and ethyl acetate. There is nothing wrong with these two components, they are recognized throughout the world as  common congeners found in rum. The only problem –and the raison d’etre of this article– is that once-common yeast strains, some that were not as efficient in producing ethanol alone, are falling in disuse for their fermentation “inefficiencies,” and by abandoning them we are also abandoning a diversity of other alcohol congeners and their derived aldehydes and esters.

Through our Rum University courses, we regularly show craft and large distillers the differences one can obtain using alternate yeasts acting on the same molasses. One of my favorite comparisons is pitting a yeast marketed by its producer as being specially designed to make light rum (with very low congener diversity) against a traditional Eau-de-vie yeast (brandy-like, high congener diversity). In both cases the distiller could adjust the heads and tails cuts to have a distillate with the same congener content, but in terms of congener diversity (particularly in the heads), there is no comparison at all.

I hope that as rum consumers become more educated about congeners they will encourage producers to return to heavier – and more complex– profiles.

Cheers,

Luis Ayala, Editor and Publisher