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.

Topping up – glass marbles

I've already described four options for topping up a new wine for storage and maturing. There's a rather ingenious alternative available for anyone who really doesn't want to add anything to the new wine. Glass marbles! After transferring the wine from the fermenter to the storage jar, simply drop in a few glass marbles until the surface level reaches the bottom of the neck of the jar. Of course you should sterilise the marbles first. Glass is completely inert and will not impart any off flavours to the wine. In fact the marbles will have no effect at all, except the desired one of raising the surface level. And of course, they can be used over and over again.

glass marbles – sterilise before use

Topping up for quality

 At the end of fermentation, the wine should be separated from the lees (sediment) and stored in a fresh vessel. If you are working with 5-litre bottles, typically, between sedimentation and volume loss, you will be able to transfer about 4½ litres, leaving a ½-litre air space above the wine. This is too much air and would impair the final quality if you simply sealed the bottle for storage. Fortunately, there are several options for topping up, some better than others, but the choice is yours:

1. Water. This is the simplest approach but of course it dilutes the wine, reducing alcohol by volume, acidity, tannin content, intensity of colour, flavour and aroma, and body. This sounds bad but some wines can benefit from judicious dilution.
2. Wine. Topping up new wine with wine from an earlier brew is often the best answer. Obviously, the added wine must be sound. Normally it should be of similar style to new wine, though judicious corrective blending is possible, for example, to increase acidity if the new wine is lacking in that department.
3. Spirits. White wines can be topped up with a neutral spirit like vodka. Red wines can benefit from an addition of brandy. This is an expensive option to be used in exceptional cases only. For example, a white wine at 13% with residual sweetness can be fortified to 15% to preserve the remaining sugar against further fermentation, producing a strong desert-style wine. Only consider this option for wines that are showing early signs of high quality, and be prepared for a long aging process.
4. Diluted spirits. For a table wine that is already the strength you want, e.g. 12%, you can top up with a 12% ABV vodka/water mix. This still dilutes all of the wine's characteristics just as water does, but it preserves the alcohol content.

In summary, Option 2 is usually the best option. Option 1 is cheap and cheerful, Option 4 is good for lighter wines, and Option 3 is for specialised purposes only.

You'll note there is no fruit juice option. Anything that adds sugar at the top-up stage is to be avoided as it is asking for trouble – flying corks, burst bottles, permanent hazes... Don't go there.