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Fermentation

Wild fermentation

Letting the microflora already present on the fruit and in the press house carry the ferment, in a succession rather than as a single organism.

Known as Fermentation spontanée where it originates. Also called Spontaneous fermentation, Natural fermentation.

Stage
Fermentation
Traditional in
Asturias, Basque Country, Normandy, Pays d’Auge and 4 more
What it most changes
Fermentation character up, freshness down
Safety
None recorded

What it is

A wild or spontaneous fermentation is one in which no yeast is added: the juice is left to be fermented by the organisms already in it, which arrive from the fruit surface, from the orchard, and — probably more importantly — from the mill, press, hoses and vessels of the press house itself. What follows is not one fermentation but a succession. A varied population of non-Saccharomyces yeasts dominates the opening days and then dies back as ethanol accumulates, ceding the ferment to Saccharomyces, which finishes it. Lactic acid bacteria usually follow in the maturation that comes after. It is the historical norm across every cider tradition and remains the required or customary practice in several of them.

Gravity and microbial successionSpecific gravity falling over eight weeks, with the organisms that dominate each part of the ferment shown above it.Apiculate yeastsSaccharomycesMalolactic, optionalSpecific gravity1050100002468Weeks after pitching
Specific gravity falling over eight weeks, with the organisms that dominate each part of the ferment shown above it.
Described in full
The gravity curve
Specific gravity falls from about 1.050 at pitching to about 1.000 at completion. The fall is not even: it is slow for the first few days, steepest between roughly week one and week three, and then flattens into a long tail.
The lag phase
Very little gravity is lost in the first days. Yeast is multiplying rather than producing much alcohol, and a wild ferment can sit apparently inert for a week before anything visible happens.
Apiculate yeasts, weeks nought to one and a half
Hanseniaspora and Kloeckera species carried in on the fruit dominate at the start. They make esters and acetic acid, tolerate very little alcohol, and die back once ethanol reaches a few percent.
*Saccharomyces*, weeks half to five
Takes over as the apiculates fail and does the bulk of the work. This band overlaps the steepest part of the gravity curve, which is the visible consequence of the takeover.
Malolactic, weeks four to eight and beyond
Optional, drawn with a dashed edge because it may not happen at all. Lactic acid bacteria convert malic acid to lactic acid once the sugar is largely gone, softening acidity and sometimes leaving a buttery note.
Why the bands overlap
Succession is a handover, not a relay. Both yeast populations are present together for days, and the aroma of the finished cider is partly decided in that overlap.
The scale is indicative
Temperature changes everything. A cold cellar ferment can run for six months rather than eight weeks, and the same succession plays out slowly rather than differently.

Why it is used

How it works

What it changes

The direction this step pushes the finished drink in, dimension by dimension. A direction, not a measurement: how far it moves depends on the juice, the temperature and how the step is carried out.

Effect on each sensory dimension. Hover or focus a dimension name for what that dimension means on CiderHQ.
DimensionDirectionWhy
Fermentation characterRaisesThe early apiculate yeasts generate acetate esters and higher alcohols in proportions a single pitched strain does not, giving the ferment-derived aroma more breadth.
Fruit characterEither wayEster production by non-Saccharomyces yeasts can amplify fruity aroma, but the same population also produces ethyl acetate, which above threshold masks fruit rather than adding to it.
AcidityEither waySpontaneous ferments are usually followed by an unmanaged malolactic conversion, which lowers titratable acidity, while any acetic activity raises volatile acidity in the other direction.
FreshnessLowersThe long, cool, unhurried ferments that spontaneous practice implies allow more oxidative and secondary character to develop than a rapid inoculated ferment does.

The chemistry and the organisms

What is actually being changed, and by what. Each entry says what that compound or organism does in cider generally; this page is one place it does it.

Compounds involved

Organisms involved

Where it is traditional

The places this step belongs to as a matter of practice. It is not a claim of exclusivity — a method can be traditional in one region and perfectly ordinary in another.

What it is done with

What can go wrong

Faults that begin at this step, or that this step makes more likely. Each one is set out with its causes and whether it can be put right.

Styles it produces

Categories in which this step is characteristic or required. Some name it in their definition; for others it is simply how they have always been made.

Recorded figures

Shown with the place, period and method each was taken under, and never averaged: the same step run in another cellar genuinely gives a different number.

Fermentation temperature12.0–15.0 °C

Villaviciosa, Asturias, Spain, 2001–2002 · Cellar temperature, spontaneous fermentation of Asturian sidra natural without added sulphur dioxide · Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31

One cellar, two harvests. It is recorded not as a recommendation but because every other figure from those ferments — the glycerol, the ester profile, the survival of apiculate yeasts to the end — is a figure obtained at this temperature and does not transfer to a warmer one.

The temperature a ferment was actually run at, which governs how much aroma is made and how much is blown off with the gas. Measured in degrees celsius.

Specific gravity1.047–1.050 SG

Villaviciosa, Asturias, Spain, 2001–2002 · Density of the apple musts entering spontaneous fermentation · Suárez Valles, Pando Bedriñana, Fernández Tascón, Querol Simón and Rodríguez Madrera, Food Microbiology 24(1):25–31

The starting gravity of the same ferments, corresponding to musts carrying under 110 g/L of sugar. That ceiling is why these ciders finish near 6.5% and why the alcohol never rose far enough to kill the apiculate yeasts — a low-gravity juice is a different microbiological environment, not merely a weaker drink.

Juice density, the practical proxy for sugar before fermentation. Measured in specific gravity.

More on wild fermentation

Every cider fermented before the twentieth century was a wild fermentation, but that historical fact obscures what is interesting about the practice, which is that it is not one process. Sequence a spontaneous cider ferment over its course and you find a changing cast. The opening days belong to yeasts that ferment poorly and produce aroma out of all proportion to what they consume: Hanseniaspora valbyensis and H. uvarum, Metschnikowia pulcherrima, various Candida and Pichia species. They produce acetate esters, 2-phenylethanol and a range of higher alcohols out of proportion to the small amount of sugar they actually consume, and they are intolerant of ethanol, so within days to a couple of weeks their own product has largely eliminated them. Saccharomyces, present initially at low numbers, then dominates and takes the ferment to dryness. Much of what distinguishes a spontaneous cider from an inoculated one was made in the first week by organisms that were dead long before the ferment finished.

Where the Saccharomyces comes from is a more interesting question than it looks. It is not abundant on sound fruit in the orchard. In an established press house it is resident — in the timber of a vat, the seams of a press, the pores of a hose — and a producer who has fermented in the same building for years is drawing on a population that building has selected. This is why spontaneous fermentation is more reproducible for a long-established llagar or farm cidery than for a new one, and why the first two or three vintages in a new building are often the least predictable. It is also why sanitising a traditional wooden fermentation hall to stainless-plant standards would destroy the thing that makes it work, and why the two approaches to hygiene are not simply degrees of the same discipline.

The regional picture is genuinely different in each tradition, not a variation on an English theme. Asturian sidra natural is fermented spontaneously in chestnut toneles, and the malolactic conversion and lactic character that follow are part of what the DOP identifies as the style. Basque sagardoa works similarly in kupelak. The Norman and Breton appellations use the fruit’s own flora and combine it with keeving, which strips nitrogen and deliberately makes the ferment slower still. English farmhouse practice fermented in oak vats in unheated buildings, and the long cool ferment that produced was structural to the style rather than incidental. Frankfurt Apfelwein has its own resident-flora tradition. Modern North American and antipodean producers who work spontaneously are doing something recognisably continuous with all of these, but usually in stainless and with a very different fruit base.

The honest account of the risks is that they are real and largely one-directional. A spontaneous ferment can stall — cider juice is nitrogen-poor to begin with, and a stressed mixed population can exhaust it — and a stalled ferment sitting warm with sugar in it is an invitation. Acetic acid bacteria will oxidise ethanol to acetic acid wherever oxygen reaches them; Hanseniaspora can leave ethyl acetate above its sensory threshold; Lactobacillus collinoides can produce the acrolein that gives an unfixable bitterness, or ropiness, or the raspberry-like framboise note; Brettanomyces can establish during a long maturation and produce 4-ethylphenol. None of these can be blended out afterwards. The producers who work this way successfully are not being casual about it: they are controlling temperature, filling vessels full, racking on judgement rather than schedule, and accepting that a proportion of lots will not be good enough to sell.

Related processes

Steps that sit alongside this one, replace it, or depend on it having been done.

What people ask next

Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.

Where to go next

Sources

What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.