THE PAST IS INDEED PROLOGUE The history and future use of bacteria in rum fermentations
Written by BRETT STEIGERWALDT
R
um is a globally popular sugarcane-based spirit, produced with an incredible range of organoleptic characteristics. It is delicious as an aged or unaged expression and forms the base of a wide variety of liqueurs. Given this versatility, it's truly exciting to see so many consumers and aficionados of all types gravitating toward this spirit category, with some products even achieving similar cult-like statuses to certain hard-to-find Kentucky bourbons. As a distiller, this spirit category can be intimidating given its raw ingredient diversity ("sugarcane or its derivatives," i.e., fresh sugarcane juice, cane syrup, cane sugar, or cane molasses). However, it's not as scary as it seems, and that vast distillate sensory range can be achieved more easily than ever before. Recent developments by Lallemand, Fermentis, and others, have given us another tool for our flavor arsenal: bacteria! Some distillers may be thinking, “What?! I'm trying to keep bacteria out of my fermentations!" But hear me out. Not long ago it was quite common to purposefully work with these microbes to yield incredibly complex
rums, with Jamaica being an excellent current and historic example. Luckily for us, several examples of these fermentation practices exist. However, before we dive deep into the technical details, a short history lesson is needed to provide more context on this fascinating new (old) world. In Jamaica from 1890 to 1920, our understanding of the rum fermentation environment improved, and a divide began to emerge within the research community, each side having valid points that current and future distillers would be wise to heed. Pairault and several contemporaries advocated for pure fermentations, using known yeast strains, and a low presence of bacteria [1]. Others like Allan and Ashby advocated that bacteria play a beneficial role in the complex organoleptic profiles of heavy rums [2, 3]. If you are new to this industry, the method that Pairault advocates is a great starting point. Once you determine your starting gravity, boil your rum wash, cool it to target temperature and pitch your desired yeast, fermentation will begin. Over time, you’ll learn how that yeast strain performs under sanitary
TABLE 1. Early 20th century Jamaican rum styles and descriptions from Cousins [5, 6]. Ester Content (g/hLAA)
Rum Style
Description
Common clean
Light rum, with principal aroma of ethyl acetate, and trace amounts of higher acid esters and aromatic higher alcohols
90-300
UK Home trade
Produced from slow fermentation. Medium bodied rum, mainly esters of higher molecular weight acids originating from bacteria.
300-500
Tea rum
Pot distilled medium bodied rum, primarily to enrich afternoon tea.
400-700
Flavored/German
Heavy rum from highly acidic long fermentation (15-21 days), utilizing fission yeasts. Primarily for blending.
700-1600
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conditions, various pitch rates, whether you’ll need yeast nutrients, etc., and you’ll determine your preferred distillation cut points. Once you’ve mastered these steps, you’re ready to explore the world that Allan and Ashby advocated — a non-sanitary rum wash with a naturally higher bacteria presence — and how it performs under similar fermentation conditions. Once you’ve determined your pitch rates and cut points, you’ll then be able to compare each distillate to determine your preferences. Remember, this is only for a single yeast, under specific conditions, and doesn’t necessarily translate to different rum washes. I could stop the article here for many rum-curious distillers and they’d be off to the races. However, let’s continue this journey through history. With the above fermentation concepts in mind, a variety of different rum marques/ styles were produced in Jamaica from 1890– 1920, and Cousins summarized them neatly (Table 1). On the technical/production side, Ashby defined many of the contemporary terms (Table 2) and provided three historical examples of Jamaican rum fermentation techniques: two types of common clean rum (CCR1 and CCR2, with ester contents of 100 g/hLAA and 1,000 g/hLAA), and a heavier bodied “flavored” rum (up to 1,600 g/hLAA) [4]. Process diagrams for each style can be seen in Figure 1. Two species of yeasts were commonly found in these fermentations (1) Saccharomyces spp. was most prevalent in the faster fermenting CCR1 and (2) Schizosaccharomyces spp. was most prevalent in the slower fermenting CCR2 and “flavored” rums, particularly as wash acidity and bacteria presence significantly increased [2, 4]. 83