Methanol

Methanol gets most of the blame for distillation’s heavy regulation. The idea of a poor quality distillate containing high levels of methanol and making people go blind is mostly fiction. The real problem stems from a few bad actors illegally making alcohol and adding methanol (because they are stupid and think all alcohols are the same) to their distillate to “stretch” their sales. This has happened a few times throughout history, during prohibition specifically, and can still happen occasionally today, a case happened in India recently. But, the deadly consequences of these few incidents have firmly entrenched the idea that poor quality distillate can make you go blind. But the facts state otherwise.

Methanol is pretty common in nature and the human body is well adapted to deal with this chemical. In fruit juices, the methanol content ranges from 1-640 mg/L with an average of 140 mg/L (WHO,1997) and in alcoholic beverages at levels of 6-27 mg/L have been measured in beer, 96-321 mg in wine and 10-220 mg/L in distilled spirits (WHO, 1997). If you consume drinks with aspartame, you could be increasing methanol in your body by 240 mg. A “typical human” produces 300-600 mg methanol per day from just normal metabolic processes (cited Lindinger et al, 1997). On a typical day, your body could easily be processing 1000 to 2000 mg (1 to 2 grams) of methanol per day, without consequences.

The lethal dose for methanol is 1 g/kg (a 75 kg (165 lbs) person needs 75 g or 94 ml (2½ to 3 oz)) and permanent visual damage occurs at 10 ml to 30 ml. These numbers seem low, but the real question is: Can distilled ethanol contain toxic levels of methanol? The short answer is: no it can not. But we still need to understand what levels can be contained in our distilled products, how low levels affect people and ways to reduce methanol content to meet regulatory requirements. https://www.ncbi.nlm.nih.gov/books/NBK482121/

Methanol is converted in the body to formaldehyde and then to formic acid (formate) which is then converted to carbon dioxide and water using folic acid (tetrahydrofolic acid/Vitamin B9). This multi-step reaction is natural, but it is the concentrations of formic acid that cause the most serious issues.

CHRONIC TOXICITY OF METHANOL – SUMMARY OF DATA CONSIDERED
https://cot.food.gov.uk/sites/default/files/cot/tox201030.pdf

When methanol is consumed in small quantities in distilled spirits, the enzyme that converts alcohols to aldehydes, alcohol dehydrogenase (ADH), has a higher affinity for ethanol, meaning the methanol tends to concentrate in the body during binge drinking and only after most of the ethanol is broken down does ADH start working on methanol, which is degraded to formaldehyde then formic acid. Formic acid is the compound that causes damage to the optical nerves, resulting in blindness. If a person drinks fruit distillate heavily every day then over the long term this may be a problem, but the reality is that the large quantity of ethanol being consumed is a bigger problem. 

Toxicity equals dose over time, so typically if we only have a few drinks, the methanol isn’t concentrated enough to cause issues.

https://www.chemistryviews.org/details/ezine/1080019/Chemistry_of_a_Hangover__Alcohol_and_its_Consequences_Part_3.html

Because formic acid causes the most damage and is limited by the body’s ability to clear it, conditions like a folic acid deficiency can exacerbate the problem. So if you are a heavy drinker, or know one, maybe get them to take some folic acid.

Separating Methanol During Distillation

If you’ve read the Internet or watched some YouTube videos you may be under the impression that methanol is removed in the foreshot and head cuts, but that isn’t the way it works. It makes sense that methanol has a lower boiling point (64.7 °C) than ethanol (78.37 °C) hence in theory it should come off the still earlier. Unfortunately, due to a variety of physical properties methanol has a sustained presence throughout the course of a distillation run. In fact, some studies have shown that there are higher concentrations of methanol in the tails cut.

Multi-step distillation is also beneficial at removing methanol, especially when using a column still for a second or third distillation of low wines. Due to hydrogen bonding with water, the first distillation cuts may not always work to remove methanol effectively. As the water level of the low wines is decreased, the separation of methanol becomes easier.

Pectin & Pectinase

For fruit distillates, avoid the use pectinase if possible and ferment the must at a low temperature (below 18C) because naturally, occurring pectinase is not active at lower temperatures. You can also flash heat the must to 50C to denature the pectinase enzyme before fermenting. Yeast selection, specifically low-temperature operators, are the best yeast for fruit wine fermentation that is going to be distilled.

https://www.sciencedirect.com/topics/engineering/pectinase

To produce commercially successful fruit spirits, control of methanol production is the priority. Without careful control, the methanol level may be in excess of legal limits but not necessarily toxicity levels.

Can You Consume Enough Methanol to Be Toxic?

It is unlikely unless you are a heavy or chronic drinker. Infrequent, short-term exposure to low levels of methanol is safe and the body handles it quite well. However, chronic drinking of spirits, or even wines, with high methanol levels over a long period of time can cause damage, not just to your liver but also your eyesight.

Your best individual customers who drink heavily are the ones that need protection from excess methanol.

References:

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Methanol production from the degradation of pectin by human colonic bacteria

R J Siragusa, J J Cerda, M M Baig, C W Burgin, F L Robbins
The American Journal of Clinical Nutrition, May 1988
Pectin is degraded by fecal bacteria in the colon. We examined the release of methanol (MeOH) by this degradation.

DOI: 10.1093/ajcn/47.5.848

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FIVS Methanol in Wine

Andrew L. Waterhouse, Gavin L. Sachs and David W. Jeffery
Understanding Wine Chemistry
This paper examines the origins of methanol in grape wine and the quantities typically found in it, as
well as in other foods such as unpasteurised fruit juices. Toxicology is also considered.