The Story of Sustainable Rum Begins With What's Left Behind

rum tasting photo

Photo credit: Distillery Serrallés, USA

Rum has long been a favorite spirit for bartenders looking to mix a crowd-pleasing cocktail. Indeed, drinks like the Mojito, Cuba Libre, and Piña Colada are staples at hip bars, college parties, and Jimmy Buffet concerts alike.

In spite of this popularity, however, the energy and resource-intensive process of producing rum is rarely considered. Though the practice of creating alcohol from a sugar base is thousands of years old, some distilleries are taking a hard look at the impact of their business—and implementing innovative solutions to make it better for the environment.TreeHugger had the opportunity to take a look at the art and science—as well as the clean and dirty—of making rum first-hand, thanks to a trip sponsored by Distillery Serrallés for members of the press.

And making rum, of course, begins with the production of sugar.

The Dirty Business of Sugar Growing

burning sugar cane field photo
Photo credit: pizzodisevo/Creative Commons

To put it in the simplest terms, rum is made by fermenting and distilling molasses. This hides several layers of complexity, however, most significantly because molasses itself is a byproduct of sugar production.

Though sugar is refined from both sugarcane and beets, cane sugar is preferred—accounting for about 70 percent of the world's sugar supply—and it is the molasses left over from this process that most rum makers use.

Intensive sugarcane production—most of which now takes place in India and Brazil—results in soil degradation and erosion, the overuse and pollution of local water resources, and the spread of pesticides and fertilizers. Furthermore, cane field burning—which is done pre-harvest to dispose of leaves and other unwanted parts of the plant—has been associated with significant increases in local air pollution and the emission of carbon monoxide and ozone.

Perhaps the most significant impact of sugarcane agriculture, however, comes in the form of habitat destruction. According to a report from the World Wildlife Fund entitled "Sugar and the Environment," sugar may be responsible for more biodiversity loss than any other crop. "Fifteen countries around the world," WWF explains in its report, "devote between ten and 50 percent of their land area to cane cultivation and in seven countries sugarcane covers more than 50 percent of the land."

Refining Sugar Creates More Problems

sugar refinery brazil photo
A sugar refinery in Brazil. Photo credit: Wikimedia Commons

The story does not end when the cane is cut from the field. First, it is brought to a mill, where raw sugar is extracted. This raw sugar is then transported to a refinery—typically located closer to the end market in North America, Europe, or Japan—where it is purified, turned into a syrup, and then processed with various chemicals to remove particulate.

The purified syrup is then boiled, allowing pure sucrose to be extracted. What is left behind becomes molasses. This molasses can then be processed and boiled again—and again, and again—resulting in more sugar extracted from each batch of syrup and a progressively more concentrated and sugarless molasses.

The effluent—or liquid and gas emissions—from this process can be toxic. Often, refineries are located in countries with relaxed environmental regulations.

The result, however, is sugar—a commodity that has become increasingly valuable as global affluence and its associated sweet tooth has increased.

The byproduct of this process—molasses—is the part most important to rum makers.

Upcycling Molasses

black strap molasses photo
Photo credit: Wikimedia Commons

In a way, rum making is upcycling: The goal is to take molasses—something that is worth comparable pennies to sugar's dollars—and turn it into a prized and valued drink.

To do this, the molasses is first mixed with water and yeast to create a fermentation base. The choice of yeast is an essential part of the process—most distillers use closely-guarded strains of their own development—and can have a strong influence over the end result: Crisp, clear rum is typically made from fast-acting, heat-loving yeast and darker, aged, more complex rum is made from slower-acting yeast.

For centuries, the fermented "beer" was distilled using a pot still. The idea is a simple one: At sea level water boils at 100 degrees Celsius but alcohol boils at 78 degrees Celsius. Thus, the still is designed to carry alcohol rich vapor away from the near-boiling water. This process is repeated several times, across several pot stills, until the desired concentration is reached.

Today, column stills are more common. In this system, often called a "continuous still" vapor is carried through and stored in two or more columns that essentially act as a series of pot stills. The advantage is that a column still can run continuously and reach much higher alcohol concentrations than a series of pot stills.

rum barrels photo

Photo credit: Distillery Serrallés, USA

Once the rum has been distilled it is placed in a barrel—typically a used oak whiskey barrel—and aged for at least a year. It is during aging that the rum gains its amber color.

The Trouble With Concentration

The distillation process, however, leaves a lot behind. Studies have found that the slop stream, called "mosto" in Spanish, contains as much as 95 percent of the pollutants embodied by the rum making process. Studies by the EPA have found toxic pollutants, in addition to lead,iron, copper, zinc, heavy metals, organic acids, amino acids, proteins, polysacharrides, and inorganic salt complexes.

The issue is one of concentration. When sugar syrup is boiled—to create pure sugar—what is left behind is the molasses and the toxins and impurities of the raw sugar. When the molasses is fermented and distilled, these toxins and elements are further concentrated. The mosto, then, is a sludge of highly concentrated impurities that have been carried down a rather dirty supply chain.

Unfortunately, there is no industry waiting to buy mosto as a base for another product. The burden of disposal falls upon rum makers.

Dealing With What's Left

For most of the history of rum production, this mosto was dumped into the most easily-accessible place: the ocean. Unfortunately, this has led to the formation of dead zones, upturned ecosystems, and critical damage to coral reef systems. In 1975, as part of the Clean Air and Water Act, this practice was outlawed in the United States. Still, most rum makers—even in the US—spread the toxic mosto in fields and in less-regulated parts of the world it still makes its way into rivers and the ocean.

The impact of rum production, when the entire life-cycle of the product is considered, is clearly significant. But does this mean we can no longer enjoy our favorite tropical cocktails with a clear conscious? Fortunately, it does not. As we will see in the next installment of this series, some distilleries are working to make high-quality rum without the sizable environmental footprint.

Read more about green liquor:
How to Go Green: Cocktails
Should You Shop For Organic Spirits?
Four Brands of Organic Booze To Get Your Party Started

The Story of Sustainable Rum Begins With What's Left Behind
Rum has long been a favorite spirit for bartenders looking to mix a crowd-pleasing cocktail. Indeed, drinks like the Mojito, Cuba Libre, and Piña Colada are staples at hip bars, college parties, and Jimmy Buffet

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