is pectin, a complex polysaccharide that is found in terrestrial plants. Critically, pectin drink considered (Table 1). bears methyl ester functional groups. Hydrolysis of these methyl ester functions releases The situation in the EU is relatively methanol. This reaction is facilitated by various enzymes such as pectinase, pectin complex, with grape- and fruit-based methyl esterase and more broadly active esterases. Not all micro-organisms, though, spirits having more relaxed limits defined. can generate methanol from pectin. For instance a study on the Brazilian spirit Presumably this is a reflection of the high cachaça found that the required yeast for fermentation, Saccharomyces cerevisiae, pectin levels in the raw materials and the common use of pot stills, which are less effective did not generate any methanol, whilst contaminating yeasts, specifically Pichia at separating methanol from ethanol. A rule-ofspp., generated 5 ml methanol/lpa. Clearly then good hygiene is an important thumb is that it is difficult to completely separate consideration for the management of methanol in final spirit. liquids that have boiling points within 55°F of each It is worth noting that alcoholic beverages are not the only dietary source other in a single-stage distillation, whereas methanol of methanol. Fruit juices, such as orange and grapefruit juices, and drinks (bp 148.5°F) and ethanol (173.1°F) have much sweetened with aspartame, contribute significant levels of methanol to the diet. closer boiling points. For spirits that yield appreciable Canning can also elevate methanol levels, and the consumption of fruits and levels of methanol a specific column, a demethylizer vegetables generally can lead to the consumption of up to 1 ml methanol per is typically employed. This is a packed column, and the day. Smokers will have increased exposure to methanol as it is formed during packing essentially adds additional capacity to improve tobacco combustion. the resolution of methanol from ethanol. An indication So it is clear that we do not want consumers to put themselves at of the volumes of spirits that can be safely consumed (in unnecessary risk of avoidable health issues, such as methanol-related the EPA context) is shown in the third column of Table malaise. But how much is too much? It seems that there is a wide tolerance 1. Based on the assumptions here, the limits set by the range to ingested methanol. As little as 10 ml of pure methanol when U.S. and Vietnamese legislature seem rather sensible, whilst consumed can cause permanent blindness by destruction of the optic the Nigerian limit is perhaps overly stringent from a methanol nerve, while 15 ml is potentially fatal. The median lethal dose though perspective. seems to be around 100 ml (3.4 fl oz or 1 - 2 ml/kg body weight of So we have seen that methanol is a largely undesirable pure methanol). In the U.S., the EPA set maximum acceptable oral component in a distilled spirit. The levels can vary substantially doses for toxic substances, defined as a level that will have minimal dependent on raw materials employed, fermentation hygiene and impacts on health over a lifetime. For methanol the EPA has set this the distilling plant configuration used. The analysis of methanol to be 2 mg/kg body weight/day. in ethanol The measurement of methanol in ethanol is requires relatively best performed using gas chromatographic TABLE 1: sophisticated (GC) analysis, a mature technique that applies analysis, using GC, distillation theory to separate compounds in although there are the vapor phase and then enables detection some other potential after separation. Whilst most if not all largedevelopments in the scale distillers will own GC equipment SAFE VOLUME MAXIMUM METHANOL d pipeline that may lead and have personnel competent to run COUNTRY OF SPIRIT/ML VALUE (G/LPA) to a low-cost sensor and maintain the instrumentation, there Australia/New Zealand 8 50 technology. The hope, are also laboratory subcontracting if not expectation, is that options available to check spirits for 100 Brazil 5a this would give distillers methanol in cases of concern. In better access to methanolour laboratory we are working to EU 2 - 15 b 27 - 200 detection technology and develop a low-cost methanol sensor Mexico 0.3 - 3 c 130 - 1300 help to reduce the incidences for making the monitoring of of methanol toxicity worldwide. methanol in the presence of high Nigeria 0.005 80000 As a consumer, the safest advice ethanol concentrations more with regard to methanol avoidance straightforward for the growing Thailand 0.24 1700 is to know the provenance of what spirits industry. USA 3.5 a 140 you are consuming. The regulatory limits for methanol in drinks depends Vietnam 3 160 on the country. In many Paul Hughes, Ph.D. is assistant professor a countries the legislation Maximum methanol levels defined by volume (v/v), i.e., ml/lpa of food science and technology at Oregon b is straightforward, but in EU levels dependent on spirit classification State University in Corvallis, OR. For c Mexico sets both minimum and maximum methanol levels for tequila Europe the EU legislation more info visit www.oregonstate.edu or call d Based on 2 mg/kg body weight of methanol/day, an average body weight of (541) 737-4595. varies depending on the
METHANOL LEGISLATION in distilled spirits
80 kg and a spirit of 40% ABV
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