Debaryomyces hansenii

Debaryomyces hansenii honours two great mycologists in its name, Anton de Bary and the Dane Emil Christian Hansen who first grew yeasts in pure culture; myces is simply fungus. It is a true yeast of the family Saccharomycetaceae, and it is, beyond question, the dominant yeast of cured meat, reaching a million living cells in every gram of a dry-cured sausage or ham. For much of its history it went by a second name, Candida famata, its asexual form, though modern molecular tools have shown that old identification unreliable and often muddled with related yeasts.

Its defining quality is an extraordinary tolerance of salt. Where common baker's yeast falters not far above ten per cent salt, Debaryomyces hansenii will grow in brines approaching saturation, at concentrations that arrest almost everything else, and it takes the cold and the low water activity of a curing chamber in its stride. That is precisely why it flourishes where its competitors cannot, on the salted, drying surface and in the salted interior of cured meat, and why it has become a model organism for the study of how life survives salt at all.

Its usefulness is threefold. It deacidifies: by consuming the lactic acid the starter bacteria have made, it gently raises the surface pH, softening a young sausage's sharp tang into a rounder, mellower maturity. It builds flavour: strongly lipolytic and proteolytic, it breaks fats and proteins into a wealth of aroma compounds, the esters, alcohols and savoury, nutty notes of a well-aged product, and by consuming oxygen and curbing the aldehydes of fat oxidation it holds rancidity at bay. And, remarkably, it protects: selected strains suppress unwanted moulds and, more valuably still, repress the very genes by which Aspergillus and Penicillium make ochratoxin, so a healthy Debaryomyces flora is a living guard against mycotoxin in a dry-cured ham.

For most of the craft's history Debaryomyces was never added; it simply arrived, borne on the raw meat and the walls and air of the curing house, and colonised the surface as part of the wild flora that a good cellar was prized for. Only recently, as its gifts have been understood, have selected strains been offered as deliberate starter and protective cultures, spread on the surface or mixed into a sausage, to bring the benefits of the best house flora to a maker who lacks a centuries-old cellar.

In practice a curesmith may rely on the native Debaryomyces of a good ageing room or inoculate a chosen strain, often alongside a noble surface mould such as Penicillium nalgiovense and the bacterial starters. Where it is added it is handled like any culture, kept cold, rehydrated and applied to the surface or mixed through, and given the cool, humid, salty conditions it loves. Its presence shows as a pale, matt, even bloom and a rounding of flavour; its absence, or its replacement by wilder yeasts, as a coarser, sharper, less predictable result.