While most homebrewers know about esters, due to their role in creating flavors during yeast fermentation of alcohol, many cannabis consumers and businesses aren’t very knowledgeable about these exciting flavor and scent chemicals. Recent research has shown potentially notable medical effects, and one company even has a patent on some esters of THC.
While the term “ester” was coined in 1848 by the German chemist Leopold Gmelin, likely as a contraction for “essigäther,” which means “acetic ether” in German, their discovery goes back almost a century earlier. In 1759 the Count de Lauraguais performed the first synthesis of the ester ethyl acetate, marking one of the first, if not the first, examples of an ester being synthesized. Esters are derivatives of “a carboxylic acid, in which the hydrogen atom of the hydroxyl group has been replaced with an alkyl group,” and their structure is the product of an alcohol combined with the carboxylic acid.
The Role of Esters in Flavor and Scent
Like terpenes, esters are very common in plants, and are the cause of many of the odors and flavors of the plants we smell and food we eat. For example, wintergreen gets its odor and flavor from the ester methyl salicylate and pears smell and taste like they do because of propyl ethanoate. Similarly, some of the flavors and scents of cannabis are a result of esters.
Esters vs. Phenols
Both esters and phenols are responsible for flavors and scents, but different types of flavors and scents. In the context of beer brewing, ester flavors are seen as desirable, good flavors, and phenol flavors are generally seen as undesirable, or bad flavors, but it depends on the beer and the palate of the person drinking it. Broadly speaking, phenol flavors are usually earthier or smokier, but they can also be clove-like.
What Do Esters in Cannabis Do?
Before he passed, the Father of Cannabis Research, Raphael Mechoulam, was very involved in researching esters in cannabis. Specifically, Mechoulam was looking at cannabidiolic acid methyl ester, which is cannabidiolic acid that has gone through a process of esterification. As his research demonstrated, esters are responsible for more than just flavor and may have medical benefits. Mechoulam’s team found that cannabidiolic acid methyl ester “is a potential medicine for treating some nausea and anxiety disorders and possibly other disorders ameliorated by enhancement of 5‐HT1A receptor activation.” A follow up study was done by Mechoulam and his colleagues where they gave cannabidiolic acid methyl ester to rats and found it “might modulate the sleep–wake cycle by engaging the hypothalamus.”
Research by Mahmoud A. ElSohly at NIDA’s cannabis research facility looking at cannabis esters made from acidic cannabinoids, and found that “CB-1 receptor assay indicated that the esters, as well as the parent acids, are not active.” That means they did not have an impact at the CB-1 receptor, and thus, should not produce feelings of intoxication/euphoria. ElSohly’s team also observed that 4-terpenyl cannabinolate “showed moderate antimicrobial activity against Candida albicans ATCC 90028.”
Aurora Cannabis actually has a patent on certain THC esters, but it is not clear if they are actively using their patented esters in any of their cannabis products.
Their Role in Alcohol Brewing
As esters are “formed by the reactions of organic acids and alcohols created during fermentation,” they play a big role in the brewing of alcohol, specifically, how yeasts impart different flavors and scents to alcohol. While other flavors can be added to beer and other alcohol by adding fruit, spices, and other botanicals, the flavor from esters is from yeast fermentation and is influenced by three main factors: the characteristics of the yeast, wort composition (nutrients), and the conditions of fermentation (environment).
Some strains of yeast are known to produce higher levels of esters, such as the yeasts used in Bavarian wheat beers which often have high amounts of isoamyl acetate (a banana-like flavor). Wort composition can be simplified to the nutrients the yeast has access to and higher concentrations of sugar, zinc, and amino acids tend to lead to more esters. Other things, like dissolved oxygen and lipid content, can reduce the production of esters. The fermentation environment also plays a major role and it seems that shallower, more open, fermentation vessels lead to more esters.
Esters aren’t just a major feature in beer, but also in spirits, most notably Jamaican rum. Jamaica has long been known for producing high ester rums, but in 1934 they passed the The Rum (Ether Control) Act, which, for the first time, imposed an ester limit for rum. That limit of 1600 gr/hlAA of esters is still enforced to this day by Jamaica’s Spirits Pool Association. If anyone was concerned that limit has to do with health and safety, it does not, and has a lot more to do with some quirks of the global alcohol market during the era of Prohibition.