Methanol & Other Impurities
Methanol is formed when fermenting beverages high in pectins – eg grapes and berries. Starting with a grain or sugar based wort, in a clean fermentor with a yeast culture from a well aereated source will result in small/none formed.
Carl from Hambletonbard (makers of Alcotec yeasts) details.
Methanol, you will typically get around 2 or 3 parts per million (or milligrams per litre if you prefer) of methanol produced during fermentation of a standard 6kg type Alcotec – this is extremely low even compared to commercial products. We don’t have a great deal of data on methanol because whenever we have tested for it we have got extremely low results.
Mike explains about the pectin.
The methanol comes from the pectin, which mainly composed of methyl esters of galactose. When pectin breaks down, by enzymes introduced by microorganisms, or deliberately introduced, the methyl esters combine with water to produce methanol, so the aim should be to leave the pectin well alone if you can.
I think Jack would agree that what he means is that fermenting at a high temperature, or adding pectin enzyme, or trying for an abv higher than 12% all increase the risk of methanol being produced, so his advice about low temperature fermentation, adding no exra enzymes, and a target lower than 12%abv is all good stuff.
You are already being exposed to methanol from other sources. Some fruit juices are naturally high in methanol – for example apple juice can have 0.2-0.3% methanol, or if derived from pulp by enzymatic degradation, the levels can be 2 to 3 times higher.
The lethal dose of methanol is at least 100 ml that is equal to about 80000 mg or you need 27000 liters of mash at least to get that amount.
also from the webpage: “Dietary surveys have shown that an extreme consumer of orange juice drinks slightly over 2 litres/day. The estimated maximum intake of methanol based on this consumption would be 455 mg for a 60 kg adult which is below the maximum advisory intake of 600 mg per day for a 60 kg adult, recommended by the Department of Health.”
So if we stay under 600 mg per day we are safe, that’s the same as 200 liters of mash per day or about 70 liters of 40% alcohol per day if you weight is 60 kg.
total amount of methanol in mash expressed in ml is about 0.1 ml = nothing.
The Long Ashton Research Station did some studies that showed that ciders and apple juices clarified with pectic enzymes are higher in methanol due to the demethylation of juice pectins. The methanol content varied from 10 to 400 ppm in the test samples. I don’t know which fruits are highest/lowest in pectin content, but apples are commonly considered the highest.
This is why all the old books on cider making refer to a condition called “apple palsey” – it’s the massively painfull hangover from the high methanol content. In order to prevent this (I’m sure distilling the pectin turns it into methanol) distillers must fully clarify any fruit wine before cooking it. Rather than use clarifiers, put the wine into 2 or 4 liter plastic jugs (only filled half full) and freeze them solid, then thaw them out, this will result in perfectly clear (and chill- stabilized) wine ready for distilling. After the thawing is complete or maybe as much as a week after, the wine will be crystal clear.
Stephen Alexander reports that commercial spirits contain small levels of methanol. ‘Food Chemistry’ by Belitz more methanol is produced in fruit fermentation than in grains. Brewers do not remove the methanol in beer and wine because methanol is not especially toxic at low concentrations. You are looking at between 0.4%-1% methanol in wines and brandies and smaller amounts in beers. Distillers remove almost all the methanol in most cases. Ever notice how vodka produces clean hangovers and wines (particularly reds) give you very nasty hangovers? Methanol. That, and dehydration!
Methanol is an especially nasty type of alcohol because the body tries to break it down the same way it metabolizes, or breaks down, ethanol, the type of alcohol in beer, wine and other drinks. Metabolizing ethanol produces chemicals less toxic to the body than alcohol. Unfortunately, if the same chemical action is performed on methanol the result is formic acid, lactic acid and formaldehyde.
Formaldehyde attacks nerve cells, especially the optic nerve and can damage the liver and kidneys. Formic acid and lactic acid also attack the kidneys and liver. Most people who have drunk methanol die of severe and sudden kidney and liver failure.
Chronic methanol drinking will cause optical damage. The stories of moonshine causing blindness comes from U.S. prohibition times where some bootleggers used to cut moonshine with methylated spirits to increase profit.
It isn’t the yeast that controls methanol, it’s what you’re fermenting. I believe yeast has very limited metabolic pathways around methanol. Quoting from http://www.madsci.org/posts/archives/jul2000/965090996.Bc.r.html –
“Basically it can be produced biologically in 2 ways; through the oxidation of methane by methane monooxygenase, or by the reduction of formaldehyde, by methanol dehydrogenase (and this reaction normally works in the reverse direction).
It’s true that some methanol can be produced during fermentation, but this is not derived from the ethanol or by carbohydrate oxidation. It is produced in small amounts, either by non-enzymatic reactions or through the reduction of formaldehyde.”
Methane isn’t present in our washes, so the culprit is formaldehyde. I believe the pectins in fruit are methylated and can break down in the wash into formaldehyde. But so long as your wash has only pure fermentable carbohydrates, you can expect essentially zero methanol. There’s a bit more in this discussion of methanol here: http://yarchive.net/med/methanol_poisoning.html
Ethyl acetate, OTOH, is produced spontaneously whenever acetate is present with ethanol. There are several possible sources of acetate during fermentation. In general, acetate is formed by oxidation of ethanol. (In fact, acetate is the ‘end-product’ of our own metabolism of ethanol). In fermentation, oxidation of ethanol into acetate can happen as a result of desperate yeast metabolizing its own ethanol, or by contamination with other yeasts or bacteria.