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Death in a Bottle

by Andrew McNaughton

There’s dying for a wine, and then there’s dying in a wine. Fortunately the latter is reserved for the yeast cells and is altogether a good thing. When wines are fermented a second time in the bottle, they take on a bubbly personality. The release of CO2 from the growing yeast cells pressurises the bottle as the gas dissolves in the wine. When opened, the wine returns to atmospheric pressure and the CO2 comes out of solution, producing a satisfying fizz. So far so good. Where’s all this death in a bottle business?

The base wine (
cuvee ) has additional yeast and sugar added (the liqueur de tirage) to initiate the secondary fermentation. Far from simply being a method of producing CO2 for a few bubbles, this process introduces a host of characteristic aromas and flavours. These don’t come from the gas bubbles when the wine’s drunk, but rather from the dead and dying yeast cells.

The process of yeast cell death is called autolysis, the name alluding to a quiet self-destruction as the yeast expires in its own filth. It’s the oozing yeast cell contents which give the wine a fuller body, subtle aromas and creamy mouthfeel. This soup of peptides and fatty acids works on the wine for years as it ages in the bottle. It also affects the foaming properties of the wine. All in all, it’s what makes wine makers cry when they get it right - and when they get it wrong. Their aim is not just to ensure a wine is healthy when it’s young. They must also see the wine through to the end of its life. In effect, leave a good looking corpse.

Saccharomyces cerevisiae shown under phase contrast microscopy.

The problem with all this is it takes time: years of time. Naturally, we all want to enjoy the quality only patience can bring - now! One potential solution is to mutate the
Saccharomyces cerevisiae yeast by exposing it to ultraviolet light. Because yeast grows so fast, it’s quick to produce mutants which die at a more convenient rate. Similar outcomes have been found when one ‘killer’ S. Cerevisiae strain is mixed with a ‘sensitive’ strain. All that’s needed is blood on the floor, how that’s achieved is secondary.

Pressurising a wine bottle from a cylinder of CO
2 produces a sparkling wine, but one lacking the depth of a true méthode champenoise. You always knew it was wrong, now you have proof.

So, the next time you pop the cork, spare a thought for the many tiny lives which gave it their all for your bubbly extravagance. They had guts, now you’re drinking it.

If you want to know how scientists can tell which plant the sugar used in the secondary fermentation came from, keep watching. To whet your curiosity, it involves carbon isotopes and a quirk of plant physiology - damn, have I give
n it away?

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