Surface Yeasts
Also known as Yeast, Film yeasts
The yeast community of the cured surface and interior, led by Debaryomyces hansenii, that deacidifies, builds flavour and lends a pale bloom, alongside a scatter of lesser and sometimes spoilage yeasts.
Every cured surface carries a community of yeasts, and in a dry-cured ham or sausage they gather in great number, often a million to the gram. They share the surface with the noble moulds and the lactic bacteria and, like them, tolerate the salt and low water activity that see off most microbes. Chief among them, and the one that matters most, is Debaryomyces hansenii; but Candida, Pichia, Yarrowia, Rhodotorula and others appear alongside it, drawn from the raw meat and the curing environment.
Their collective work, led by Debaryomyces, is largely welcome. They consume oxygen, limiting the oxidation that turns fat rancid; they deacidify, using up lactic acid to soften a young product's sharpness; and, being lipolytic and proteolytic, they release aroma compounds that deepen flavour. A light, even yeast growth also gives the pale, matt bloom seen on some traditional sausages, softer and greyer than the white felt of a noble mould.
Not every yeast is a friend. The useful ones, Debaryomyces above all and selected strains of Yarrowia and Candida, are prized; but Rhodotorula, with its pink carotenoid pigments, reads as spoilage and discolouration, and any yeast overgrowing into a thick, sticky or greasy film in a damp, still chamber becomes a fault rather than a virtue. The line between a helpful bloom and a spoiled surface is drawn by control, of humidity, airflow and the starting flora.
A curesmith manages the yeast flora as part of the surface: encouraging the good yeasts through a clean, well-loved ageing room or a deliberate Debaryomyces starter, and holding the rest in check through controlled humidity and air movement so that no single organism runs away. The individual yeasts carry their own entries; this is the family they belong to.