05 August 2021

Alcohol from sugar?

I've met quite a few folk who've tried to make alcohol by fermenting sugary water. When it doesn't work, they've always got a reason – it gets too hot in my apartment when I'm out at work, or, the yeast's been lying around for nearly a year and probably died, or, it started fine but then stopped. Probably I didn't stir it enough. Or. . . 

One guy even argued with me, citing a chemical equation that 'proved' (to his satisfaction) that one mole (not the furry kind) of glucose can be turned into 2 moles each of ethanol and carbon dioxide, using some yeast 'as a catalyst', he said. Well, a little learning is a dangerous thing, as Pope observed.

Yeast is not a catalyst. It's a living organism. It releases enzymes that first convert sucrose into glucose then, through several intermediary stages, into ethanol, carbon dioxide and smaller quantities of many other organic compounds. To work this miracle, the yeast cells have to multiply, get to work, and finally die on the job. But, unlike sugar, yeast cells and the enzymes they produce are not composed solely of carbon, hydrogen and oxygen. They are much more complex than that. In particular, they require nitrogen and phosphorous (in the form of phosphates). These are not found in sugary water!

The commonest commercial yeast nutrient is diammonium phosphate (DAP) but before you go rushing off to your friendly neighborhood chemist, there is good news – a well balanced must made with fruit juices and fresh ingredients usually contains enough in the way of nitrogen, phosphates and trace elements to support a healthy yeast colony and yield a decent wine. Just don't expect sugary water to do the same. It won't.

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