Friday, 14 December 2018

Invertase

My pal R came up to visit from The Holy Land part of the River Barrow valley. I won't be more specific because the questions we had to thrash out were mostly about distillation. The Gardai keep a watchful eye on distillers because rogue manufacturers who concentrate alcohol by distillation have rarely read chemistry at university and have only a hazy, seat-of-the-pants, idea about the relative boiling point of a) water 100oC b) ethanol 78oC c) methanol 65oC d) congeners ???oC. Earlier this year I alluded to a case where several deaths were cause from methanol poisoning at a Balkan wedding serving home-made cherry brandy. Hundreds of similar instances happen every year.

Distillers first make a ferment of yeast and sugar (and some additives because yeast cannot live on sugar alone). Pure white p'ison sugar costs money, so anything with sugar in it will do: apples, sprouting grain, potatoes, and of course grapes. With an alcohol-tolerant strain of yeast, reasonably tight control of temperature and sufficient food, this mash might finish up at 20% ethanol by weight. Depending on how pure the inputs are, you're going to have water and more or less ethanol and less or more methanol and the other shite. I suppose you could start with dustbin full of beyond-sell-by-date cakes and see what happens. The mash is then distilled by heating up the water and condensing the vapours. First comes the methanol, then the ethanol and finally as the temperature rises from78oC to100oC the ethanol concentration falls off and you're getting [impure] water.

There are reasons for having a really fast fermentation: to crank up the concentration of alcohol to the max before the dead yeast start to make the kitchen smell rank. If you're using sucrose = cane sugar = the stuff you buy in the supermarket; then the yeast has to do extra work before it starts to convert the sugar into alcohol. That's because sucrose is a disaccharide: its made up of one glucose and one fructose [see R] and the currency of metabolism is glucose so splitting the disaccharide and reconfiguring the fructose are pre-requisite actions before the actual ferment can begin.

Glucose is aka blood sugar [it's our energy currency as well as yeast's] or dextrose. Me and R had a bit of a barney because he refused to accept that 'glucose' is chemically identical to 'dextrose'. Sometime food ingredient engineers will put dextrose on the table of contents to hide that fact that they are lurrying in the sugar into the product. Dextrose is a funny name for a girl but an evocative name for a chemical. It rings of dextrous, dexterity and right-handed as opposed to sinister with all those negative left-handed associations. Dextrose gets that name because if you shine polarised light through a bottle of glucose the light will be rotated clockwise = to-the-right. This is quantitative: higher concentration = more twist, longer light-path = more twist. Sucrose also performs this turn-right party-trick. Fructose otoh, the sinister member of the couple, rotates light even further anti-clockwise. As your solution of sucrose gets broken down, more fructose goes into solution and the light inverts.

You can do the breakdown by brute force by adding acid - such as citric acid: the Go To acid for food use: like all chemical reactions things go faster if you heat them up. Or you can do it elegantly with an enzyme called sucrase aka invertase. Enzymes are proteins which miraculously make biochemical reactions go faster at normal temperatures. R's 'recipes for rot-gut' advised using a jolt of citric acid and heat to increase the initial concentration of mono-saccharides and then cool the mix down before adding the yeast. The reaction [glucose --> alcohol and carbon dioxide] is, of course, carried out by enzymes too. I suggested that R might try to source commercial invertase to do the pre-processing. Enzymes really do work fantastically more efficiently than chemical reactions.

1 comment:

  1. Invertase is an enzyme that catalyzes the hydrolysis (breakdown) of sucrose (table sugar). The resulting mixture of fructose and glucose is called inverted sugar syrup. Related to invertases are sucrases. invertase

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