So the ginger-beer plant was a bona fide "dual organism", rather like lichens. Everything pointed to a true symbiosis. For instance, when Ward tried to feed the bacteria with dead or feeble yeast cells, the experiments failed. The plant emerged only from a marriage of equals, which needed time: it took several days for the partners to find and embrace one another. No one could have predicted that the crude home brew of country folk would reveal a phenomenon new to science - what Ward called "symbiotic fermentation".

It was landmark research. Yet as the study of symbiosis fell out of fashion, Ward's work sank into obscurity. Vindication of a sort came half a century later, when a research team decided to investigate kefir . Ward had also been interested in this yogurt-like drink, made from fermented milk, and popular in the Caucasus mountains of southern Russia and Georgia, and he had begun to investigate its secrets.

Legend has it that the Prophet Muhammad first gave kefir curds to Christians living near Mount Elbrus with strict instructions never to give them away. All the same, kefir curds did eventually turn up in a laboratory where, just as Ward had predicted, investigators identified a symbiotic collaboration between yeast and bacteria.

Years after Ward's pioneering work, Soviet researchers discovered a further instance of symbiotic fermentation. A yeast and a bacterium apparently cooperate to form the "tea fungus" or kombucha that thrives on sweetened tea. After a few days, the liquid acquires a pleasant acidity and a peculiar fruity taste that eastern Europeans once regarded as ideal for gastric upsets.

Indeed, not so long ago, even ordinary bread owed its distinctive taste and consistency to microbial liaisons. The traditional baker's yeast or "barm" passed from baker to baker was found in the 1950s to consist not only of the conventional baker's yeast Saccharomyces cerevisiae but at least one other yeast, as well as one or more bacterial species. By cooperating, this microbial syndicate fermented a greater number of carbohydrates than any of the various microbial components alone. The bread that resulted was surely like nothing you can get today.

Today's commercial ginger beer is also much altered, purged of both its alcohol and its symbiotic liaisons. It is possible that Ward's own lovingly reconstituted ginger-beer plant survived into the 1940s. Max Walters, now 82, says he made and drank the stuff in the Botany School at Cambridge just after the Second World War. But no one knows what happened to it after that. Thankfully the ginger beer plant is still available here.

Read the rest of this article at New Scientist magazine

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From issue 2362 of New Scientist magazine, 28 September 2002, page 50

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