Native yeast or cultured yeast

This is one of the most ideologically loaded decisions in winemaking, and it is worth separating what is known from what is asserted.

It is also frequently misdescribed. Spontaneous fermentation is not the absence of a decision: it requires a clean, warm, microbiologically healthy cellar and a producer who monitors it closely.

Inoculation adds a large population of a known strain, which outcompetes the resident flora almost immediately. Fermentation starts fast, runs predictably and finishes reliably.

Spontaneous fermentation begins with Hanseniaspora, Candida, Metschnikowia and others, which contribute their own metabolites for the first days before ethanol suppresses them. Saccharomyces then completes the ferment.

The compositional consequences are measurable. Spontaneous ferments generally show higher concentrations of some compounds, including glycerol and certain esters and higher alcohols, and differ in volatile acidity.

The risks are also real: slower starts, greater vintage-to-vintage variability, higher chance of sticking, and more scope for spoilage organisms including Brettanomyces to establish.

The resident population in an established winery lives substantially on equipment and building surfaces rather than arriving on the fruit, which considerably weakens the claim that spontaneous fermentation expresses a vineyard.