Out of a pickle

FOR breakfast, a bit of Saccharomyces cerevisiae and, perhaps, a dash of Lactobacillus. For lunch, some Acetobacter or Leuconostoc mesenteroides—but look out for any stray Streptococcus faecalis. In the evening, probably back to S. cerevisiae. From bread and yogurt, via pickles, kimchi and vinaigrette, to beer and wine, people have co-opted many microbes to work their magic in the service of flavour.

It is only in recent years, though, that science has looked into how the bacteria and fungi involved do their fermenting—consuming one set of molecules and excreting a tastier set, or one that preserves the food, or one that inebriates the imbiber. Those who make traditional cheeses and salamis follow recipes that, through tight control of temperature, salinity or moisture, shepherd the growth of a special community of unicellular critters to end up with a desired flavour. But experimental chefs such as David Chang in America and René Redzepi in Denmark are trying to extend fermentation’s range. That has resulted in, for example, Hozon, Mr Chang’s commercial flavouring made from nuts or beans fermented with Aspergillus, a mould more usually used with rice to make sake, or with soya to make miso.

Such efforts often call on science in support. So it was that Rachel Dutton, a microbiologist at Harvard University, began to receive packages from experimental chefs. Inside she found novel fermented foods, inoculated with this bug or that. The chefs wanted to know whether their creations were safe to eat. Dr Dutton, who came to Harvard to look into the microbial particulars of cheese, found herself cataloguing the bugs in these novelties, and then considering whether the microbiology of fermented foods has more general lessons to teach about how such bugs collaborate and fight. Working with Benjamin Wolfe of Tufts University, for example, she is looking at which interactions between tasty bugs on cheeses can prevent the invasion of dangerous ones.

Others, too, are interested in the field. A group of researchers from Belgium and Switzerland—both famous producers of chocolate—showed, for instance, that the fermentation of cocoa pulp is dominated at first by fast-working but delicate Hanseniaspora yeasts. These, though, are later roughed up and booted out by more robust yeasts such as S. cerevisiae and Pichia kudriavzevii. And micro-organisms’ effects on food and drink are not restricted to fermentation of the ingredients. A paper published this week in mBio suggests that bacteria have a lot to do with a wine’s terroir, since those covering the fruit and the leaves, as well as the roots, all seem to originate in the soil.

Mastery of the underlying ecological mechanisms and rhythms of micro-organisms has implications far beyond the culinary. On a tree trunk, in the ocean or in the human gut, thousands of microbe species live cheek by jowl. That makes it hard to understand what is going on. A simplified version of this complexity would therefore be welcome. Dr Dutton and Dr Wolfe suggest, in a paper just published in Cell, that many fermented foods fit that bill perfectly.

Such foodstuffs host mixtures of a few dozen species, and these are usually of a kind that can be grown easily in laboratories. If studying fermentation in this way revealed general principles about how bugs live together, then it would be possible to imagine recruiting such communities to do jobs other than fermenting food and drink: acting as pesticides, for example; or treating waste water; or turning various sorts of leftovers into fuels.

This is the opposite approach to that taken in the emerging field of synthetic biology, which tries to design bespoke individual organisms to perform particular tasks. But executing those tasks with families of naturally occurring creatures instead of individual artificial ones might be both easier and less contentious.