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Methanol (wood alcohol) is such a trivial health issue, in these sorts of levels, that there doesn't seem to be much recent study, unless the USDA has figures in some internal report. Since methanol is so widely present in plant foods, measurements of its occurrence are trivial and uninteresting.

As guidance, pectic substances (the major source of methanol in plants) amounts to 0.5 to 1.0% of the fresh weight of apples. So a 200 gram apple has 1 to 2 grams of pectin. Pectin starts out about 80-90% methylated, then during fruit ripening becomes about 40% methylated, because internal plant enzymes do the cleavage. I'm going to assume that the methyl groups are about 5% of the total pectic substance (a data-free analysis), so that makes the 2 g of pectin in an apple have about 50-100 mg of potential methanol. Assume that only half of these methyl groups are cleaved, so now we're down to 25-50 mg of methanol in one single apple.

Pectin, and it's de-esterifying enzymes, are found in nearly every fruit, from strawberries through to bananas. Apple juice would be especially high in methanol, since manufacturers treat it with commercial pectin esterase to get rid of cloudiness, and in this case there isn't anywhere for the methanol to go except to stay in solution.

Although pectin isn't degraded by mammalian enzymes in the human gut, this doesn't matter because plants themselves contain the enzymes. Moreover, bacteria in our large intestines will be able to cleave pectin in most cases, so any residual methylated pectin will form methanol in the bowel.

Really, the quantitative difference between the amount of methanol that causes blindness in chronic alcoholics who drink it as a cheap drunk, and the amounts of methanol in either apple juice or aspartame, is so great that it's really a scam to pretend that there is no difference.

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.

Johan found ..
In http://archive.food.gov.uk/maff/archive ... orange.htm orange juice contains 10 to 50 times as much methanol as sugarmash.

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.

Jack comments ...
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&Grosch list an assay of about 50 different components of about 10 different distilled beverages. The US and Scotch whiskies had methanol levels around 0.2 to 0.3 %. Kevin Brown has scanned in some MeOH chromatograms from a column application guide published by Supelco of Bellefonte, PA. (a vendor for chromatography supplies). Check out http://amlc.uvi.edu/distill/meoh.html for details.