Can methanol be formed when brewing a rice wine?

Question

Most people consider home wine brewing safe, regarding the methanol dose that is being produced.

Wikipedia mentions 2012 methanol poisoning incident in Cambodia, caused by drinking home-made rice wine contaminated by methanol.

How did it happen? Does the rice contain pectins (like in grapes or berries) which are responsible for methanol formation? Or the incident was rather caused by the addition of extra (unprofessionally distilled) alcohol contaminated by methanol?

Answer 1

Agreeing with dmtaylor and the references he quoted, but adding a few foot notes:

• Saccaromyces Cerevisiae (beer/bread yeast) and S. Bayanus (wine/distilling yeast) are genetically incapable of producing more than minute levels of methanol during fermentation;
• Certain bacteria are capable of producing significant amounts of methanol, but only under the right conditions, under which they partially oxidize methane into methanol. This requires the presence of methane (a byproduct from bacterial decomposition) and oxygen.

The bottom line is that as long as you observe proper sanitation (ie. avoid bacterial contamination) and manage your oxygen levels (ie. aerate/oxygenate your must/wort/wash prior to pitching yeast and keep it anaerobic thereafter) you have NO chance of methanol occurring in more than trace quantities.

In short, a proper fermentation is safe.

The horror stories of methanol-containing booze wiping out entire parties are the result of mixing methanol into beverages intended for human consumption (either accidentally or deliberately). While bacterial contamination could conceivably produce significant amounts of methanol, the conditions for this to occur are so far removed from a normal fermentation that you will definitely spot it, starting with the odors of the bacterial decomposition that produces the methane required, and the fatal levels of oxygen you would have to had introduced into your fermenter.

Answer 2

Interesting. This is the first I've really looked into this. A quick Google search led me to a study by the US National Library of Medicine National Institutes of Health. This study found that fermentations of the following ingredients can sometimes lead to relatively high quantities of methanol in fermented beverages:

Bananas, Sugarcane, Agave, Plums

The concentration of methanol found in these fermented beverages ranged from 0 to about 1.5-2% at the most. Some governments like the EU actually find these amounts to be acceptable, while most other governments do not. The US government for instance limits methanol concentration to a maximum of 0.1%, which is highly conservative, and approximately matches the blood-alcohol toxicity level for methanol of approximately 0.10-0.15%. Yet in many instances where death has occurred, the methanol content in these beverages was found to be as high as 16-25%! This leads me to believe that either foul play was involved, or unskilled distillers made a bad product, leading to many or most of the methanol-related deaths, considering that natural undistilled fermentations appear to be limited to around the 0.2% level. This also makes sense in that most naturally fermented beverages cannot exceed about 12-14% ethanol content -- the yeast just gets too tired before it can ferment any higher than that. And with many (most?) yeast strains, the ethanol limit is even lower than that, maybe 8-9% for a lot of them.

The US study also states: "Methanol is produced during fermentation by the hydrolysis of naturally occurring pectin". So it appears you may be correct that pectin plays a critical role in methanol production.

So, does rice have pectin? Some sources indicate yes. But, is it a real concern? That, I'm still not exactly sure of. I'm guessing, probably not. I believe the deaths we see in the news are being caused mostly by distillers who don't really know what they are doing. And if you are not distilling, I think the risk of adverse health effects or death is probably extremely low, assuming you're consuming only moderate quantities of course. High ethanol levels of >0.40% blood-alchol level will probably kill you before the tiny fractions of percents of methanol will... unless you're drinking distilled beverages. And I'm sure we need not go into the statistics and risks of ethanol poisoning here, that's beside the point. As always... consume any alcoholic beverage at your own risk, be responsible, don't be stupid, all good things in moderation, etc.

Interesting question. Thanks for bringing it up. Wish I could be more help. I might look into this topic some more later when I have more time. Cheers.

References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5028366/

https://healthfully.com/list-foods-containing-pectin-5903391.html

https://foodworksblog.wordpress.com/2011/06/05/rice-white-or-brown/

Answer 3

You cannot produce dangerous levels of methanol through fermentation alone.

Fermenting a sugar wash produces next to no methanol.

Fermenting grains produces very little methanol.

Fermenting fruit produces a little bit more.

In the worst of cases, you would need to drink 10 gallons of fermented fruit juice to get enough methanol to have an ill effect.

If you fermented 10 gallons of an apple wine or cider, then distilled it carefully, the methanol foreshot is generally going to be less than 2 oz which at about 24 grams of methanol per oz = 48 grams of methanol AT MOST. Per the National Institute of Health, the median amount of methanol to kill a person is 56.2 grams. So yeah...you'd have to drink 10 gallons of wine to give yourself methanol poisoning. You'll die from quite a few other things first if you tried.

Interesting fact, they treat methanol overdose with ethanol...That's right. Ethanol dilutes and allow methanol to to be metabalized. That doesn't mean the methanol isn't hurting you, it just makes it less damaging. So yeah, you aren't going to methanol-poison yourself with fermented beverages.