Sourdough Starter Cultures: Microbiology, Maintenance, Types & What Goes Wrong

What is a sourdough culture?

Sourdough is not a single organism. It is a stable, self-regulating ecosystem: a community of wild yeasts and lactic acid bacteria (LAB) that have established a working balance inside a flour-and-water medium. The yeast provides leavening — carbon dioxide to lift the dough — while the LAB produce organic acids that lower pH, preserve the bread, create the characteristic sour flavour, and in rye bread, perform an essential structural function that no other process can replicate. [src-bakerpedia-sourdough, src-pmc-sourdough-microbiome]

More than 50 species of lactic acid bacteria and over 20 species of wild yeast have been documented across sourdough starters studied worldwide. No two starters from different environments are identical, which is why a starter established in a Polish bakery from local rye flour will develop a different microbial character to one established in a Sicilian bakery from durum wheat. [src-pmc-sourdough-microbiome]

![img-sdc-01]

The three main types of sourdough culture

Professional bakers choose between three fundamentally different sourdough formats. The right choice depends on production scale, consistency requirements, available skill and the flavour profile target.

See comparison table: Sourdough culture types — classification, characteristics and professional use for the full breakdown.

Type I — Live traditional starter

A Type I sourdough is a continuously maintained culture of wild yeast and LAB, produced and kept in the bakery. It is refreshed (fed) with flour and water on a regular schedule — daily or twice daily for an active room-temperature culture; weekly for a refrigerated maintenance culture. Fermentation temperature runs 20–30°C. At peak activity, the starter reaches a pH of 3.8–4.5 and is used at a dosage of 20–30% on flour weight for wheat breads, or 30–50% for rye breads. [src-ireks-compendium-sourdough, src-bakerpedia-sourdough]

The Type I starter gives the most complex, most variable flavour — useful when authenticity and terroir are part of the product story. It also requires consistent daily attention and expertise to maintain. If a baker goes on holiday without leaving maintenance instructions, the starter can die.

Domson products for Type I propagation: Böcker Reinzucht-Sauerteig Pure Sourdough Starter 1 kg provides a defined pure-culture starter for in-bakery propagation. Lesaffre Livendo Starter LV-2 and Lesaffre Saf-Levain LV1 are propagation cultures with defined LAB strains. [src-böcker-brand, src-lesaffre-sourdough]

Type II — Industrial liquid concentrate

A Type II sourdough is produced industrially at 30–50°C for 2–5 days, generating a very high LAB count (above 10^8 cfu/g). Yeast activity is often low or absent. The product is supplied as a ready-to-dose liquid — the baker adds it directly to the dough along with commercial yeast for leavening. No in-bakery cultivation is required. [src-ireks-compendium-sourdough, src-pmc-lab-sourdough]

This format offers high consistency batch-to-batch and suits high-volume production where flavour must be repeatable. Acidity is high and concentrated: Zeelandia Bioferm Ciemny, a confirmed product in the Domson catalogue, has a pH of 2.4–2.8 and a Sauregard value of 250–260 SH°. Dosage is calibrated to the rye flour content of the recipe: 2.5% for a 50% rye dough, rising to 4.0% for a 100% rye formula. [spec-bioferm-dark]

ULDO Dark Sauer (also in the Domson catalogue) is a paste-form Type II product with a broader dosage window of 2–8% on flour weight, and a pH of 2.5–4.5 with total acidity of 140–150 SH°. This wider range reflects the paste consistency — at 2% it adds character and depth; at 8% it significantly acidifies the final product. [spec-sauer-dark-rye]

Allergen note: Zeelandia Bioferm Ciemny contains liquid whey in its ingredient list and declares MILK as a confirmed allergen. This is uncommon among sourdough concentrates and must be communicated to customers with dairy allergies or dietary restrictions. [spec-bioferm-dark — FOOD SAFETY FLAG]

Other Domson Type II liquid products: Böcker Flüssigsauer 200 15 kg; Böcker Bio Le Chef Organic 2 kg; Backaldrin BAS Light and Dark Liquid Rye Sourdough 12 kg; Bas Weizen Liquid Wheat Sourdough 12 kg; Zeelandia Amore Wheat Sourdough 13 kg.

![img-sdc-08]

Type III — Dried inactivated sourdough (powder or paste concentrate)

A Type III sourdough has been dried — typically by spray or drum drying — after fermentation. The microbial cells are killed by the heat; what remains is the accumulated organic acids, flavour compounds and aromatic molecules. The product contributes sourness and flavour but cannot leaven on its own. Commercial yeast must be added separately to provide gas. [src-ireks-compendium-sourdough, src-aacci-sourdough]

The advantages: very long shelf life (6–18 months at ambient), no refrigeration requirement, instant dispersibility, and flavour consistency. The limitation: no live microbiology means no further acidification during dough rest — the acid level is fixed.

Zeelandia Superkwas (Sourdough Dry 25 kg) is a grey powder with moisture below 16.5%, dosed at 1.3% on flour weight. It is primarily a flavouring agent with rye flour as its main component (79%) and acidity regulators E330 (citric acid), E270 (lactic acid) and E327 (calcium lactate) providing the remaining acid content. Shelf life: 180 days below 25°C and 75% RH. [spec-superkwas]

Puratos O-tentic Durum is a more complex product: dried durum wheat sourdough combined with active yeast, antioxidant (ascorbic acid E300) and enzymes. It is correctly described as an "active bakery component based on sourdough" rather than a pure inactivated sourdough. The yeast fraction is still alive. Usage rate is 4% on flour weight; no additional commercial yeast is needed. Acidity specification: 45–65 ml/10g total acidity; dry matter 94–100%. Shelf life 12 months at 16–20°C, maximum 65% RH, packed under modified atmosphere. Once opened: use within 7 days at 0–7°C. [spec-otentic-durum]

O-tentic Durum is certified Kosher, certified Halal, free from alcohol and free from pork. It is not suitable for coeliacs (contains wheat gluten). [spec-otentic-durum — FOOD SAFETY FLAG]

![img-sdc-09]

Other Domson Type III products: Puratos Sapore Fidelio Sourdough 10 kg; Puratos Sapore Rigoletto Sourdough Powder 25 kg; Lesaffre Rye Sourdough AS ECOL 11 kg; Bas Turbo 500 Sourdough Concentrate 12 kg; ULDO Sauer Dark Rye Sourdough Concentrate 25 kg.

---

Reading sourdough acidity on spec sheets

Two different measurement conventions appear on the spec sheets of Domson sourdough products. Understanding them matters when comparing sourcing options or checking a delivery is within specification.

See comparison table: Sourdough acidity measurement — units explained in data.json.

SH° (Sauregard): The standard European bakery acidity unit. It measures how many millilitres of 0.1 M sodium hydroxide are needed to neutralise 10 grams of sample to pH 8.5. A higher SH° means more total acid. Zeelandia Bioferm Ciemny: 250–260 SH°. ULDO Dark Sauer paste: 140–150 SH°. These are concentrated industrial products — the acid is diluted many times in the finished dough.

ml/10g (Puratos method C005M001): Functionally equivalent to SH° — ml of 0.1 M NaOH per 10 g sample. Puratos O-tentic Durum: 45–65 ml/10g. This lower range reflects the fact that O-tentic is a dried powder with 94–100% dry matter, not a liquid concentrate.

pH: Measures hydrogen ion activity on a logarithmic scale. More intuitive to read at a glance, but does not reflect total acid concentration. A liquid concentrate at pH 2.6 with 250 SH° contains far more total acid than a thin culture at the same pH with 30 SH°. Always check both pH and total acidity when evaluating a concentrate.

The practical target for a correctly fermented sourdough dough going into the oven is pH 3.8–4.5 and a dough SH° of approximately 8–20, depending on bread type. The concentrated products reduce to these levels when dosed into a full recipe. [src-ireks-compendium-sourdough]

---

The organisms and what they do

![img-sdc-01]

The dominant lactic acid bacteria in sourdough belong to the family Lactobacillaceae (genus Lactobacillus and its 2020 reclassified sub-genera). The dominant wild yeasts are Saccharomyces cerevisiae and Kazachstania humilis (formerly Candida humilis). [src-pmc-sourdough-microbiome, src-lesaffre-sourdough]

See comparison table: Sourdough microbiology — key organisms and their roles in data.json for species-level detail.

Homofermentative vs heterofermentative LAB

This distinction matters practically because it controls flavour and gas production:

Homofermentative LAB (e.g. Lactiplantibacillus plantarum, Pediococcus pentosaceus) convert sugars almost exclusively to lactic acid. They produce no CO2. They acidify rapidly and give a mild, yogurt-like sourness. They are often dominant in warm (26–30°C), high-hydration fermentations. [src-pmc-lab-sourdough, src-bakerpedia-sourdough]

Heterofermentative LAB (e.g. Fructilactobacillus sanfranciscensis, Levilactobacillus brevis, Limosilactobacillus fermentati) convert sugars to lactic acid, acetic acid and CO2 simultaneously. They produce the sharp, wine-like acetic notes associated with traditional San Francisco-style or German rye sourdoughs. They tend to dominate in cooler (18–24°C), stiffer doughs. [src-pmc-lab-sourdough, src-ireks-compendium-sourdough]

The ratio of lactic acid to acetic acid (LA:AA ratio) is the primary lever for flavour control. A ratio above 4:1 gives mild flavour; a ratio approaching 1:1 gives sharp, complex flavour. [src-ireks-compendium-sourdough, src-pmc-lab-sourdough]

---

Controlling flavour: temperature and hydration

The four-quadrant rule of sourdough flavour:

![img-sdc-04]

| Condition | Effect | |---|---| | Warm (26–30°C) + wet dough (≥80% hydration) | Fastest fermentation; high lactic acid output; mild, clean flavour | | Warm (26–30°C) + stiff dough (≤65% hydration) | Balanced lactic/acetic; classic country bread character | | Cool (18–22°C) + stiff dough (≤65% hydration) | Highest acetic acid proportion; most complex, sharp flavour; long fermentation; overnight retard achieves this | | Cool (18–22°C) + wet dough (≥80% hydration) | Slowest fermentation; lower overall acidity; mild, mellow flavour |

Source: [src-ireks-compendium-sourdough, src-pmc-lab-sourdough]. These are directional guidelines, not absolute thresholds — exact outcome depends on starter microbiology, flour type and fermentation time.

---

Why rye bread needs sourdough (it is not optional)

In wheat sourdough, low pH is primarily a flavour and shelf-life tool. In rye bread, it is structurally essential and cannot be substituted.

Rye flour contains high levels of pentosans — water-soluble polysaccharides that form a gel when hydrated. Rye also contains active amylase enzymes that break down starch during baking. Without sourdough acidification to pH 3.8–4.5:

1. The amylases remain active through baking and destroy starch structure — the bread interior turns gummy.
2. The pentosans do not hydrate correctly, leaving the crumb collapsed and dense.
3. The bread cannot form a coherent structure without gluten to compensate — rye has minimal gluten development.

When the dough reaches pH 3.8–4.5, the amylases are inhibited and the pentosans hydrate properly, giving the open, springy rye crumb. [src-ireks-compendium-sourdough, src-pmc-lab-sourdough, src-aacci-sourdough — c41]

This is why Bioferm Ciemny's dosage table scales with rye content: the more rye, the more acid needed. At 100% rye, the dosage is 4.0% — and the spec sheet instructs pre-soaking the rye flour and concentrate together in 70% of the dough water for 2–3 hours before mixing to ensure full acid penetration. [spec-bioferm-dark]

![img-sdc-07]

---

Sourdough's nutritional benefits (context, not a health claim)

Sourdough fermentation produces meaningful changes in the nutritional profile of bread:

• Phytate reduction: LAB-produced acids and the enzyme phytase degrade phytic acid during long fermentation. Studies indicate up to 80% reduction in phytic acid in sourdough bread versus yeasted bread under optimal long-fermentation conditions, increasing the bioavailability of iron, zinc and calcium. This figure is condition-dependent (flour type, fermentation time, temperature) and should not be used in marketing copy without legal review under EU Regulation 1924/2006, as mineral bioavailability claims approach health claim territory. [src-pmc-lab-sourdough, src-aacci-sourdough — c43 — flag for legal review]
• Lower glycaemic response: Organic acids slow starch digestion; sourdough bread typically has a lower glycaemic index than equivalent yeasted bread (single-source — flag for human review before making this a product claim).
• Extended shelf life: The acidic pH (3.8–4.5) and antimicrobial compounds produced by LAB inhibit mould and spoilage bacteria, extending shelf life without synthetic preservatives. [src-pmc-lab-sourdough, src-bakerpedia-sourdough]
• Gluten modification: Proteolytic activity of LAB at low pH partially hydrolyses gluten proteins, improving dough extensibility and potentially reducing subjective gluten sensitivity (this does NOT mean sourdough is safe for coeliacs — it is not). [src-aacci-sourdough, src-pmc-lab-sourdough — c48 — FOOD SAFETY FLAG]

---

Building a live starter from scratch

See formula card: Building a Wheat Sourdough Starter — Day-by-day guide in data.json.

![img-sdc-03]

Key rules that apply regardless of starter recipe:

• Water quality: Heavily chlorinated tap water can slow starter establishment because high chlorine concentrations attack the wild yeasts and LAB before they establish. In most municipal water supplies, the chlorine level is low enough that tap water is usable directly. If in doubt, or when establishing a new culture, use filtered water or rest tap water in an uncovered bowl for several hours before use. [src-kingarthur-sourdough-starter — c37]
• Flour type for establishment: Wholegrain and rye flours carry a higher native microorganism load than white flour. Starting with wholegrain accelerates establishment. Many bakers switch to white flour once the starter is stable (from day 4 or 5). [src-bakerpedia-sourdough-starter]
• Temperature: Target 21–26°C. Below 18°C, development slows significantly. Above 30°C, undesirable bacteria may outcompete LAB. [src-bakerpedia-sourdough-starter, src-kingarthur-sourdough-starter]
• Judging activity: The starter is ready when it reliably doubles in volume within 4–8 hours of feeding. The float test (drop a teaspoon in water — it floats if gas production is sufficient) is a useful proxy check. [src-bakerpedia-sourdough-starter, src-kingarthur-sourdough-starter — c33]

![img-sdc-02]

---

Maintaining a production starter

A bakery starter is a professional tool that needs consistent protocols, not improvisation.

Feeding ratios: A starter is fed by weight, not volume. Common ratios range from 1:1:1 (starter:flour:water) for a fast (4–6 h) turnaround, to 1:5:5 for a slow (10–12 h) overnight cycle. Higher ratios dilute the acid and slow activity; lower ratios refresh quickly but can build excessive acidity. [src-bakerpedia-sourdough-starter, src-kingarthur-sourdough-starter — c27]

Refrigeration: A starter can be held at 2–8°C for 1–2 weeks between feeds without significant loss of viability. Remove from the fridge 4–8 hours before use, feed, allow to peak, then use. [src-kingarthur-sourdough-starter — c34]

Hydration convention: Most professional bakery starters are maintained at 100% hydration (equal flour and water by weight, producing a thick batter). Stiffer starters (50–60% hydration, like the French levain ferme) develop more acetic acid character. Wetter starters (125–150% hydration) ferment faster and produce more lactic character. Adjust to your target flavour profile. [src-bakerpedia-sourdough-starter, src-ireks-compendium-sourdough]

---

Fault diagnosis and remedies

See fault table: Sourdough starter faults — causes, diagnosis and remedies in data.json for the full table.

When to discard — no exceptions

Two scenarios require immediate discarding of the entire starter with no attempt at rescue:

Pink or orange streaks or patches on the starter: This indicates contamination by non-LAB organisms — one possible cause is Serratia marcescens or similar pigment-producing bacteria, though definitive identification requires lab testing. Regardless of the specific organism, the pink/orange pigment is a reliable visual indicator that the culture has been overtaken. Discard, sanitise the container thoroughly, and begin again. [src-kingarthur-sourdough-starter — c36 — FOOD SAFETY FLAG]

Black or dark fuzzy mould on the starter surface: This indicates mould contamination — likely Rhizopus, Aspergillus or Penicillium. Do not scrape off the mould and continue. Mycotoxins produced by moulds can penetrate well below the visible surface; the contamination is not limited to what you can see. Discard entirely. [src-kingarthur-sourdough-starter — FOOD SAFETY FLAG]

Grey liquid on top ("hooch")

The grey or dark liquid that forms on top of a neglected starter is ethanol produced by the yeast as sugar runs out. It is not harmful. Stir it back in or pour it off, then feed the starter. It is a sign of starvation — feed more frequently or refrigerate between uses. [src-kingarthur-sourdough-starter — c35]

Flat bread from a live starter

The most common cause is using the starter past its peak. A starter that peaked 3–4 hours ago is already declining — yeast populations have produced maximum gas and are running out of sugar. Use the starter at peak (domed, maximum volume, still slightly bubbly on the surface). If the starter repeatedly fails to produce adequate leavening, reassess fermentation temperature, feeding ratio, and flour type. [src-bakerpedia-sourdough-starter, src-kingarthur-sourdough-starter]

---

Storage of commercial sourdough concentrates

![img-sdc-05]

The storage requirements differ significantly by product type — read spec sheets carefully.

| Product type | Temperature | Humidity | Freeze? | After opening | |---|---|---|---|---| | Liquid concentrate (e.g. Bioferm Ciemny) | 0–25°C | Dry | NO — do not freeze [spec-bioferm-dark] | Use promptly; keep sealed | | Dried powder (e.g. Superkwas) | Below 25°C | Max 75% RH [spec-superkwas] | Not recommended | Keep sealed; monitor for clumping | | Active dried concentrate (O-tentic Durum) | 16–20°C sealed | Max 65% RH [spec-otentic-durum] | Not stated | 0–7°C; use within 7 days [spec-otentic-durum] | | Paste concentrate (ULDO Dark Sauer) | Max 30°C | Max 75% RH [spec-sauer-dark-rye] | Not recommended | Reseal; follow shelf life |

Shelf lives confirmed from spec sheets:

• Zeelandia Superkwas (Sourdough Dry): 180 days [spec-superkwas]
• ULDO Dark Sauer: 9 months [spec-sauer-dark-rye]
• Puratos O-tentic Durum: 12 months [spec-otentic-durum]
• Zeelandia Bioferm Ciemny: 12 months [spec-bioferm-dark]

Delivery check: If a liquid sourdough concentrate arrives outside its stated pH or acidity range, or shows off-odour on opening, do not use it. Document and report to your supplier. Bioferm Ciemny that has frozen in transit (spec states 0°C minimum — do not freeze) may show phase separation or precipitate; reject and notify supplier. [spec-bioferm-dark — FOOD SAFETY FLAG]

---

Allergen summary for sourdough products

All sourdough concentrates in the Domson catalogue contain gluten (wheat, rye, or both). This is inherent to their flour content and cannot be avoided.

Additional allergen notes, from spec sheets:

• Zeelandia Bioferm Ciemny: Contains MILK (liquid whey is an ingredient). Also contains gluten: wheat, rye, barley confirmed present. Note: the spec is dated 2011 — always obtain the current allergen declaration from Zeelandia before communicating allergen status to customers, as sesame was added to the EU mandatory allergen list (Regulation 2021/382) after this spec was written. [spec-bioferm-dark — FOOD SAFETY FLAG]
• Zeelandia Superkwas: Gluten (WHEAT and RYE) confirmed. Cross-contamination risk: BARLEY, OAT, SPELT, EGG, SOYA, MILK, SESAME. Note: allergen declarations must be verified against a current spec sheet (this is from 2019). [spec-superkwas — FOOD SAFETY FLAG]
• ULDO Dark Sauer: Gluten (rye, barley, wheat). Cross-contamination risk: milk, sesame, soya, lupinus, eggs. Note: this spec is dated 2014 — verify current allergen declaration with ULDO Polska before use in any customer-facing material. [spec-sauer-dark-rye — FOOD SAFETY FLAG]
• Puratos O-tentic Durum: Gluten (WHEAT) confirmed ingredient. Mustard: possible cross-contamination only. [spec-otentic-durum — FOOD SAFETY FLAG]

None of the sourdough concentrates reviewed are suitable for people with coeliac disease. O-tentic Durum is explicitly labelled Non Suitable for coeliacs on its spec sheet. [spec-otentic-durum]

---

Regulatory note

There is no single harmonised EU definition of "sourdough" as of 2026. Some EU member states have national standards or established traditions for what constitutes authentic sourdough production (for example, French "pain au levain" legislation distinguishes breads made with live cultures from those made with inactivated cultures, and Italy has national bread labelling provisions). Labelling claims about sourdough character should be checked against applicable national food law in each market. Note: the regulatory source cited for this article (src-fst-eu-sourdough-definition) has been flagged as potentially misidentified — the linked EFSA URL covers food enzymes, not sourdough definitions. Verify the regulatory position with a qualified food lawyer and with national-level legislation before using any sourdough labelling claim in a specific market. [src-aacci-sourdough — c51 — FOOD SAFETY FLAG: verify national law before marketing use]

---

Coverage notes and confidence

Solid (spec-confirmed): Dosage, pH, SH°, shelf life, storage temperature and humidity, and allergen declarations for Superkwas, Bioferm Ciemny, O-tentic Durum and ULDO Dark Sauer. These are first-party spec-sheet data, checked directly.

Solid (multi-source corroborated): Sourdough microbiology (LAB species, yeast species, fermentation types I/II/III, acid ratios, temperature effects) — confirmed by two independent PMC academic sources plus BAKERpedia and IREKS Compendium.

Thin (single-source): Böcker liquid concentrate SH° and pH ranges (brand website only, no spec sheet for Le Chef available in this session). Phytic acid reduction percentage ("up to 80%") — cited in two sources but specific conditions that produce 80% are not confirmed.

Flagged for follow-up: (1) O-tentic Durum Böcker Le Chef spec PDF failed to load — a different PDF (Martin Braun Krokella, unrelated) was returned from the same local_path; the O-tentic Durum spec was loaded correctly from a separate path and is confirmed. (2) Glycaemic index claim not included in body — insufficient independent confirmation in this research session. (3) EU regulatory landscape for sourdough labelling is evolving — recommend a follow-up check with a food law expert before using claims in marketing.