A bacterial culture is a named, living population — and the three genera printed together on most fermented-food labels are not the same kind of organism at all. What "live" means technically, and why cold storage is a piece of microbiology rather than presentation.
The sediment in an unfiltered bottle lifts off the bottom in slow clouds whenever the bottle is moved, then takes several minutes to settle back. Under a microscope that sediment resolves into rods, most of them one to three micrometres long — some drifting singly, some in short chains, a few branched into forks. That material is the culture. It is what separates a fermented drink from a flavoured infusion, and it is also the reason the bottle has to be kept cold.
What is a bacterial culture?
In food science, a culture is a defined population of living microorganisms, deliberately grown and maintained, then added to a food to do a known job. The word carries both senses at once: the act of growing the organisms, and the material that results.
A culture is named at three levels. Genus, such as Lactobacillus. Species, such as Lactobacillus delbrueckii. And strain — one particular isolate, usually carrying a deposit number from a public culture collection. The strain level matters more than it looks: two strains of the same species can behave quite differently in the same vessel, with different growth rates, acid tolerance and aroma compounds.
A defined culture lists its strains in known proportions. An undefined culture — the kind traditional food-making runs on — is a community carried forward from batch to batch, stable in behaviour and never fully catalogued.
Lactobacillus, Bifidobacterium and Bacillus are not the same kind of organism
Three names turn up on most fermented-food labels, in a single list that hides how far apart they sit biologically.
Lactobacillus
Gram-positive rods that do not form spores. They are anaerobes that tolerate air, and they take their energy from fermenting sugars into lactic acid. Homofermentative species produce lactic acid almost exclusively, through glycolysis; heterofermentative species run the phosphoketolase pathway and produce acetic acid, ethanol and carbon dioxide alongside it, which is why some ferments finish sharp and gassy and others simply sour.
They are fastidious eaters, unable to make many of the amino acids and vitamins they need, so they grow in rich substrates — milk, fruit, grain, vegetable juice — and not in plain water. The genus has also changed shape recently: in 2020 it was split into twenty-five genera, so a name like Lactobacillus plantarum is now correctly Lactiplantibacillus plantarum.
Bifidobacterium
Also Gram-positive, but from a different phylum altogether — the Actinomycetota, closer to soil actinomycetes than to lactobacilli. The cells are frequently branched into Y and V shapes; Henri Tissier described them in 1899 and named them for that forked form.
Their metabolism is distinct enough to be diagnostic. Bifidobacteria run the bifid shunt, which hinges on the enzyme fructose-6-phosphate phosphoketolase and yields acetate and lactate in a theoretical ratio of three to two; its presence identifies the genus. Most species are strict anaerobes, among the more oxygen-sensitive organisms used in food, which makes them demanding to keep alive in a sealed bottle.
Bacillus
Rod-shaped, Gram-positive bacteria defined by a single trait: they form endospores, dormant structures that let the organism sit out conditions most vegetative cells could not. Bacillus species are aerobic or facultatively anaerobic, and common on plants, in soil and on drying grass. Bacillus subtilis, the type species, is one of the cultures used in ETRAFLORA ferments and is sold on its own as a 100 ml bottle of live culture at 30% concentration.
What a starter culture actually does
A starter is an inoculum: a live, actively growing population added at the beginning of a batch, so that fermentation starts from a known point rather than from whatever happens to land in the vessel.
- Speed. Cells arrive already adapted to the substrate, so the lag before exponential growth is short.
- Direction. Which organisms dominate decides which acids, gases and aroma compounds appear.
- Dominance. As the starter acidifies the batch, falling pH narrows what else can establish itself.
- Repeatability. The same starter, substrate and temperature give a batch that resembles the last one.
Bacterial populations move through four phases: lag, exponential growth, a stationary plateau, then slow decline as the substrate runs down. A starter skips the uncertain part of that curve.
The oldest version of this is backslopping — keeping part of a finished batch and carrying it into the next, indefinitely. A sold starter is the same idea in stabilised form. Fermentum Concentrate is one: a one-litre living starter built on thirty-six ingredients, sold either as a drink or as the beginning of a home ferment. It sits with the rest of the starter cultures in the catalogue.
What “live” actually means
Two words do most of the work here, and they are not synonyms. Viable means the cell is intact, metabolising and capable of dividing. Culturable means it will grow into a visible colony on nutrient agar under a specified set of conditions.
Counts on a label are almost always culturable counts, expressed in colony-forming units. The phrasing is deliberate: a colony may grow from a single cell or from a chain of four stuck together, so a colony-forming unit is a unit of counting rather than a headcount.
Between the two sits a well-documented state written VBNC — viable but non-culturable. These are cells with intact membranes and measurable metabolic activity that will not form colonies on a plate, often after stress from cold, acid or a shortage of nutrients. It is why a flow-cytometry count and a plate count of the same sample rarely agree, and why “live” is best read as a measurement of one population, made one particular way, on one particular day.
Heat does not undo fermentation, incidentally. The acids, gases and aroma compounds the culture produced all remain in the liquid. What heat changes is the population: a heat-treated ferment is still a ferment, but it is no longer a live one.
How temperature and time change the count
Every species has three cardinal temperatures — a minimum below which it will not grow, an optimum where it grows fastest, and a maximum above which it stops. Mesophilic lactobacilli tend to sit around 30 to 40 °C; thermophilic dairy species run nearer 43 to 45 °C.
Above the maximum, growth does not merely stop; inactivation begins, and it is roughly logarithmic. Food microbiology describes this with the D-value: the time at a given temperature needed to reduce a population by ninety per cent. D-values fall steeply as temperature rises, so a few degrees can be the difference between a culture that survives a process and one that does not. Hence a temperature ceiling. ETRAFLORA holds fermentation below 45 °C for the whole cycle and pasteurises nothing, which is set out on the production page.
Below the minimum, the opposite happens. Metabolism slows, division largely stops and the cells persist. Chilling is not killing but slowing, with rates falling by roughly half for each 10 °C drop across the moderate range. Slow is not zero, though: a refrigerated live ferment keeps acidifying gently and its viable count keeps easing downward, which is what a shelf life on a living product describes.
Oxygen, acidity and the rest of the bottle
Oxygen sorts these organisms sharply. Bifidobacteria are strict anaerobes. Lactobacilli tolerate air but mostly lack catalase, so hydrogen peroxide accumulates when oxygen is available. Bacillus species are comfortable with it. This is why fermentation vessels are closed, why headspace is kept small, and why an opened bottle changes faster than a sealed one.
Acidity is self-limiting. Undissociated organic acids cross the cell membrane freely, dissociate in the neutral cytoplasm and acidify the cell from the inside, so a culture eventually inhibits itself with its own product. In a closed vessel dissolved carbon dioxide adds pressure; ETRAFLORA ferments at around ten atmospheres, which is why the concentrate label asks you to open it slowly and hold the cork until the gas escapes. Sediment and haze in a living drink are simply biomass. They belong there.
Why living drinks travel cold
The cold chain is not presentation. If nothing has been pasteurised and there are no preservatives, colourings or flavourings, temperature is the only remaining control on what the population does between the vessel and the glass. ETRAFLORA drinks are made in small hand-filled batches under a HACCP framework, tested microbiologically batch by batch, then held and shipped chilled between +5 °C and +19 °C in insulated packaging. Refrigerating them on arrival is a piece of microbiology, not housekeeping.