If methanol has always been a source of anxiety for distillers, it’s probably because few of us actually know much about it.
True, many distillers can talk about how their process removes methanol and about how minimizing its presence is critical to making safe, potable products. However, much of what distillers share is rooted in myth and rumor.
Making Sense of Methanol
For distillers to understand methanol and how it relates to their spirits, they first need to understand its nature and the dangers it poses.
Sometimes called wood spirit or other names, methanol is considered the simplest of all alcohols. Comprised of a single carbon attached to three hydrogens and an OH group, methanol’s chemical formula is CH3OH. Like ethanol, methanol is colorless and has an alcoholic odor, making it almost indistinguishable from ethanol in its liquid form. The main difference between methanol and ethanol is that ethanol has an extra CH2 group (called a methylene), which means ethanol has a higher molar mass. That’s also why methanol has a boiling point below that of ethanol, at 148.5°F (64.7°C).
It’s important to understand methanol because it’s commonly found in distilled spirits and because it’s often in high enough concentrations to be lethal to humans. When ingested, methanol is rapidly absorbed into the body to be broken down by alcohol dehydrogenase, mostly in the liver. Alcohol dehydrogenase oxidizes methanol into formaldehyde, which is subsequently broken down into formic acid, which cannot be easily removed by the body. Formic acid is incredibly toxic to the body and attacks the central nervous system, particularly those nerves related to the retina.
The lethal dose for methanol varies by person, but the U.S. National Library of Medicine says that it can be as little as one gram per kilo of body weight—or just a few ounces for a 200-pound man. Below that level, however, it can deal serious damage to the ocular nerves, causing blindness—though at what concentration that occurs is up for debate.
What’s not up for debate is that methanol should be a serious concern both for distillers and for government agencies that aim to ensure public safety.
The Makings of Methanol
Almost every alcoholic drink has at least minute amounts of methanol. That’s thanks to its presence in the raw materials used to make these drinks as well as general yeast metabolism.
For methanol to be found in quantity in a spirit, there are generally only two pathways.
The first way takes place during fermentation, through the enzymatic degradation of pectin. Pectin is a structural part of the cell walls of many plants, particularly fruits; technically, it is a complex heteropolysaccharide that contains various sugars and galacturonans. The exact means by which pectin breaks down during fermentation is complex, but during this process, pectin methyl esterase (PME) hydrolyzes the methyl ester bonds of galacturonic acid to produce methanol.
The amount of methanol produced depends on the amount of PME active during the fermentation and on the amount of pectin available to be broken down. The yeast and other microbes can produce PME biologically during fermentation, or it can come from the fermentable material itself—generally from pectin-containing fruits such as apples or grapes. That makes brandy and other fruit distillates of particular concern for methanol presence.
The second and considerably less savory way to get a quantity of methanol in distilled spirits is through adulteration. Like ethanol, methanol is an intoxicant. While’s it’s less inebriating than ethanol, its low cost and wide availability make it a common additive for disreputable liquor dealers trying to increase their margins.
While distillers working with reputable resellers don’t need to worry about this vector for methanol infusion, it’s worth mentioning because almost all reports of consumer deaths and blindness caused by methanol ingestion are linked to this kind of adulteration—not from the degradation of pectin.
Minimizing Methanol
Removing methanol from distilled spirits can be a very tricky task.
Regardless of what many distillers have learned—and will freely tell the public—methanol can’t simply be removed in the heads during standard distillation. That’s because methanol is highly miscible with water and forms strong hydrogen bonds with it. Those bonds distort the standard boiling point of methanol, causing it to distill during the entire run, with only a slight increase in presence in the heads. Ultimately, that means methanol will be present in considerable concentrations in the heads, hearts, and tails.
The only way to combat this is for distillers to use a specialized type of still that incorporates a demethylating column. These columns are complex, must often be used continuously, and can be very expensive to operate, making them out of the reach for all but the largest of distilleries.
Instead of trying to remove methanol from their spirits, many distillers focus on preventing its production during fermentation. There are several different ways that distillers can either prevent or reduce methanol production during fermentation, and many distillers use a combination of techniques to achieve their goals.
The first and perhaps easiest way to control methanol production during fermentation is to select fermentables that contain low levels of pectin and PME activity. Both grain and molasses have low to zero available pectin and PME, therefore methanol isn’t a concern in spirits made from these ingredients. For fermentations containing fruit such as grapes or apples, the level of available pectin and PME is much higher—especially in under-ripened fruit—and distillers should be sure to select vintages that have low methanol potential. Another way to reduce pectin levels in fruit is to remove cores, stems, and skins, though that’s often not economically viable.
A second way to reduce methanol production during fermentation is by adjusting the fermentation variables that result in PME activity. As previously mentioned, certain yeast strains and other microbiota produce PME. Distillers should select yeast that have a low potential for producing PME, and they should try to minimize infection from wild yeast or bacteria strains.
Also, PME activity tends to increase at higher fermentation temperatures; given enough time, it will eventually release all the methanol that a fermentation could potentially create. Therefore, distillers should focus on keeping fermentations both cool and short to reduce the amount of potential methanol in their final spirit.
Another way distillers can reduce the amount of methanol in their fermentations is through additives. A number of different additives can reduce PME activity—most notably pectin lyase enzyme, which breaks down pectin without producing methanol. Distillers also can add acids to lower the pH of fermentations; pHs of 2.5 and below can inhibit PME activity. Unfortunately, that also tends to have a deleterious effect on the fermenting yeast and can produce a subpar product.
Perhaps the most drastic way to reduce the production of methanol in fermentation is through sterilization of the mash. PME, like many other enzymes, is sensitive to extreme temperatures; it will readily denature at temperatures above 158°F (70°C). That means that cooking fruit mashes at or near that temperature for a set amount of time is an option for distillers who want to reduce methanol potential. As with acidification, however, such high-temperature cooking may have a negative effect on the final product.
Measurement, and a Misconception
Almost all countries have legal limits on the amount of methanol allowed in their spirits, though it can vary depending on the type of spirit.
In the United States, the legal limit for all fruit-based spirits is seven grams per liter (g/L) at 100 percent ABV, which equates to 17,500 ppm at 40 percent ABV. In Europe, the highest allowable limit is 13.5 g/L at 100 percent ABV, though that’s only for spirits produced from certain raw materials. For general fruit spirits, the European limit is 10g/L.
The required method for measuring methanal content is gas chromatography (GC), and the TTB has published recommended methods for labs to use. Several other methods for measuring methanol have been proposed, though none have been formally approved by governing bodies. To ensure compliance, it’s important that distillers concerned about methanol in their products have an approved lab test their products.
Let’s address one last common misconception. While ethanol can be used as a remedy for methanol poisoning—because of its ability to inhibit alcohol dehydrogenase—it’s neither the preferred nor safest way to treat methanol poisoning, and there are many other factors to consider. Methanol poisoning should always be treated by a medical professional. If you suspect that you or anyone you know is showing symptoms of methanol poisoning, you should seek out a medical professional immediately.
Despite what some distillers may think, methanol is not the boogeyman of the spirits industry. By carefully selecting raw materials and managing fermentation, distillers can produce high-quality spirits that are both tasty and safe to consume. We’ve been doing it for hundreds of years and, with any luck, we’ll be able to continue for hundreds more.