Sourdough technology: starter maintenance, LAB–yeast synergy, acidification curves and rye vs. wheat sourdoughs

Graph showing sourdough pH drop over time from approximately 5.8 to 4.0 during a 12-hour fermentation

1. What is sourdough and why does it matter?

Sourdough is the oldest leavening technology in bread-making — a fermented culture of flour and water in which lactic acid bacteria (LAB) and wild yeast live in stable, mutually beneficial symbiosis.

The two groups do different jobs. Wild yeasts produce CO2 (which leavens the bread) and ethanol. LAB produce lactic acid and acetic acid (which give sourdough its flavour, preserve the bread naturally, and — critically in rye bread — control the structure of the dough).

Sourdough is not simply "bread with a sour taste." For rye bread, sourdough acidification is a technical necessity: without adequate acid, rye bread becomes a gummy, inedible mass. For wheat bread, sourdough is optional but delivers measurable benefits: deeper flavour, better keeping quality, improved crumb texture, and nutritional improvements (reduced phytates, better mineral bioavailability).

For professional bakers working with the Domson catalogue, sourdough technology sits at the intersection of three choices:

1. Traditional starter — a live culture maintained in-house (maximum flavour control, requires discipline and skill)
2. Industrial sourdough concentrates — ready-to-dose liquid, paste or dry sourdoughs that replace the fermentation step (consistency, convenience, speed)
3. Hybrid approaches — industrial concentrates combined with a short active fermentation step

This dossier covers all three.

2. The microbiology: LAB, wild yeast, and their synergy

Circular diagram showing the symbiotic relationship between lactic acid bacteria and wild yeast in sourdough

2.1 Cell populations

In a mature, healthy sourdough starter, lactic acid bacteria outnumber wild yeast cells by approximately 100:1. This ratio is not accidental — it reflects the different metabolic roles. LAB are small, fast-dividing, and acid-tolerant; wild yeasts are larger and slower but produce the CO2 essential for leavening.

Key LAB species found in sourdoughs include:

• Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) — homofermentative, produces primarily lactic acid
• Fructilactobacillus sanfranciscensis (formerly Lactobacillus sanfranciscensis) — the characteristic San Francisco sourdough organism; heterofermentative, produces both lactic acid, acetic acid, and CO2
• Limosilactobacillus fermentum (formerly L. fermentum) — heterofermentative

Key wild yeast species:

• Kazachstania humilis (formerly Candida humilis) — the most common wild sourdough yeast; acid-tolerant; cannot ferment maltose alone (leaves it for LAB to process)
• Saccharomyces cerevisiae — the same species as baker's yeast, but wild strains differ in behaviour and acid tolerance

2.2 What makes them symbiotic

The relationship is not accidental — it is actively mutually beneficial.

Substrate partitioning: Heterofermentative LAB preferentially consume fructose (leaving glucose and maltose available for yeast). Wild yeasts prefer glucose and maltose. This substrate division reduces competition and lets both thrive simultaneously.

Acid tolerance: Wild sourdough yeasts are selected by the acid environment that LAB create. Baker's yeast (Saccharomyces cerevisiae) from compressed yeast blocks is much less acid-tolerant; wild strains survive down to pH 3.5–4.0 where conventional yeast would stall.

Pathogen suppression: The acids produced by LAB (lactic acid, acetic acid) and the low pH suppress gram-negative bacteria, moulds, Bacillus subtilis (rope), and other spoilage organisms that would otherwise colonise the fermenting dough. This makes sourdough a self-preserving system and extends the shelf life of the finished bread.

2.3 Homofermentative vs. heterofermentative LAB

This distinction is important for bakers because it controls which acids are produced:

Homofermentative LAB (e.g. L. plantarum): ferment sugars almost exclusively to lactic acid. Result: mild, creamy sourness; no CO2 from the LAB themselves.

Heterofermentative LAB (e.g. F. sanfranciscensis): ferment sugars to lactic acid + acetic acid + CO2. Result: sharper, more complex flavour; minor additional leavening contribution. The lactic:acetic ratio in the finished bread is heavily influenced by the fermentation conditions (see Section 4.2).

Practical implication: A starter built primarily on heterofermentative LAB and allowed to ferment cool and stiff will produce a sharper, more vinegary bread than the same starter fermented warm and wet.

3. Starter maintenance: building and keeping a healthy culture

3.1 Establishing a starter from scratch

A sourdough starter begins with nothing more than flour and water. The succession of microbial activity over the first 5–7 days follows a predictable pattern:

Days 1–2: Gram-negative bacteria (including some initially undesirable species) begin fermenting. The mixture may smell slightly unpleasant. No useful rise.

Days 3–4: The pH begins to drop as LAB start to dominate. Gram-negative bacteria are suppressed by the increasing acid. The culture begins to produce visible bubbles.

Days 5–7: LAB and acid-tolerant wild yeasts have established dominance. The starter rises predictably, smells pleasantly sour and yeasty, and is ready for use once it can reliably double within 8–12 hours of feeding.

Using whole rye flour as a component in the initial build (5–10% of total flour) accelerates the process. Rye bran carries higher natural populations of LAB than white wheat flour.

3.2 The refresh cycle

A mature starter requires regular feeding to keep the LAB and yeast populations healthy. The critical parameters are the refresh ratio (old starter: fresh flour: water), the temperature, and the frequency.

Typical refresh approach (100% hydration wheat starter):

Signs of a healthy starter: Doubles within 8–12 hours of refresh at 25°C (vigorous starters may peak in as few as 4–6 hours; a healthy starter will reliably double within 12 hours); domed surface with bubbles breaking through; pleasant sour-yeasty aroma (acetic + lactic + alcohol notes); pH of ripe starter typically 3.8–4.5.

Warning signs: Grey liquid on top ("hooch") = over-acidified, starved starter. Stringy texture = proteolysis from over-acidification. Pink or orange streaks = contamination (discard and restart).

3.3 Hydration and starter type

The hydration of the starter (the water:flour ratio) affects both its flavour profile and handling:

• 100% hydration (liquid starter, equal parts flour and water): Fast-acting, more lactic acid, milder flavour. Easy to blend into dough.
• 50–60% hydration (stiff starter, levain dur): Slower fermentation, more acetic acid, sharper flavour. Longer peak window. Better for warm kitchens where a liquid starter would over-ferment overnight.
• Rye starters: Typically maintained at higher hydration (TA 180–200) to allow the pentosan network to hydrate properly.

4. Acidification curves — understanding and controlling pH

4.1 The acidification curve

When a sourdough culture is added to dough (or when a starter is refreshed), the pH follows a characteristic curve: starting around pH 5.8–6.0 (flour + water before fermentation), dropping steeply during the active fermentation phase, then levelling off as the available substrate is consumed and LAB activity slows.

A typical acidification curve looks like:

• Hour 0: pH ~5.8–6.0
• Hours 2–4: Rapid pH drop (LAB now actively producing acids)
• Hours 6–10: pH 4.2–4.8 (most of the acid is produced in this window)
• Hours 12–16: pH 3.8–4.2 (plateau — ripe sourdough)
• Hours 20+: pH may drop further to 3.5 or below (over-ripe/over-acidified)

Wheat sourdough typically plateaus at a higher pH (~4.5–5.0) than rye sourdough (~3.8–4.4) because the wheat gluten network limits gas and acid accumulation differently.

Why the endpoint matters: For rye bread, the target pH must reach approximately 3.8–4.4 to ensure that alpha-amylase is sufficiently inhibited during baking — if it is not, starch is enzymatically broken down inside the hot oven, producing a gummy, sticky crumb. The exact target pH range should be confirmed against the specific rye flour's enzyme activity (falling number) and the baker's own process conditions.

4.2 Controlling the lactic/acetic balance

The ratio of lactic to acetic acid is the primary tool a baker has to control sourdough flavour. Two key levers shift this ratio:

2x2 matrix diagram showing how temperature and dough hydration control the lactic-to-acetic acid ratio in sourdough

Temperature:

• Warm (>30°C) fermentation favours lactic acid — milder, creamy, yoghurt-like sourness
• Cool (<25°C) fermentation favours acetic acid — sharper, vinegary, more complex

Dough hydration:

• High hydration (liquid starter/dough) — favours lactic acid production
• Low hydration (stiff dough) — favours acetic acid production

This is why a traditional San Francisco sourdough (firm starter, cool overnight fermentation) tastes so much sharper than a mild French wheat levain (high-hydration, 4-hour room-temperature fermentation).

Practical tool for rye bakers: To reduce harshness in 100% rye bread without losing the structural benefits of full acidification, use warm temperatures (28–30°C) for the final stage — this biases production toward lactic acid while still achieving the required low pH.

See the comparison table below for a full parameter summary.

4.3 Measuring sourdough acidity

Professional bakeries use two complementary measures:

Important note on product acidity values: The SH° figures stated on industrial sourdough product specs (e.g. Bioferm Ciemny at 250–260 SH° ) are the acidity of the product as supplied, not the resulting dough pH after incorporation at 2.5–4% dosage. The actual dough pH after adding a liquid sourdough concentrate will be much higher (less acidic) than the product's own pH.

5. Multi-stage rye sourdough processes

Flowchart of the three-stage Detmold rye sourdough process showing time and temperature for each stage

Rye sourdough is produced using a structured, staged fermentation process — most commonly the Detmold methods developed in Germany, which are the industry standard reference for commercial rye bread production.

The number of stages is a trade-off between flavour complexity, acid development, and practical production time. See the comparison table below for a full comparison.

5.1 One-stage process

The simplest approach: the full production sour (Vollsauer) is made in a single fermentation step from a small amount of stored sour (the "keep-back" or Anstellgut).

Typical parameters: 10–20 hours at 25–28°C, TA (dough yield) 160–200.

Advantages: Simple; suitable for small bakeries; requires less equipment.

Disadvantages: Less flavour complexity; less consistent than multi-stage; sensitive to temperature fluctuations; the full acidification relies on a single population rather than a succession.

5.2 Two-stage process (Detmold)

Two fermentation stages provide better acid balance and consistency.

Stage 1 (Grundsauer / Basic Sour): Intermediate step built from the keep-back. Ferments for 15–24 hours at 23–25°C, developing the LAB population and beginning acid accumulation.

Stage 2 (Vollsauer / Full Sour): The production-scale sour. Ferments for 3–6 hours at 28–30°C. Higher temperature biases production toward lactic acid; the shorter time means the population from Stage 1 is already active, so acidification is fast.

The two-stage method is the most widely used commercial rye sourdough process in Central and Eastern European bakeries because it balances production efficiency with flavour quality.

5.3 Three-stage process (Detmold — maximum flavour)

The full three-stage process adds an Anfrischsauer (Refresher Sour) at the start — a small, high-hydration, moderately warm fermentation that builds the LAB population at relatively low stress. This three-stage succession mimics the natural microbial ecology of a well-maintained starter.

Stage 1 (Anfrischsauer — Refresher Sour): Small amount (~5–10% of total flour used), very high hydration (TA 250–300%), 5–10 hours at 25–26°C. pH drops from ~5.8 to ~5.0.

Stage 2 (Grundsauer — Basic Sour): Larger quantity, lower hydration (TA 180–200%), 15–24 hours at 23–25°C. pH drops to approximately 4.0–4.5.

Stage 3 (Vollsauer — Full Sour): Production quantity, lower hydration (TA 160–180%), 3–5 hours at 28–30°C. Final pH reaches approximately 3.8–4.2.

Why three stages produces the best flavour: Each stage creates different conditions that favour different LAB species and different metabolite ratios. The succession produces a more complex acid profile and aroma spectrum than any single-stage process can achieve.

Practical constraint: Three-stage production requires 24–36 hours of total process time and careful temperature management of three separate vessels. In industrial settings, this is managed by automated souring systems (thermostat-controlled tubs with timers and augers). Smaller bakeries typically manage with insulated containers and accurate thermometers.

6. Wheat sourdoughs — process and flavour

Wheat sourdough is structurally different from rye sourdough because gluten, not pentosans, provides the dough network. This means the acidification requirements are less strict — but they still matter for flavour and shelf life.

6.1 Types of wheat preferment

Wheat sourdough sits alongside other preferment types on a spectrum of fermentation time and acid development:

Wheat sourdough (levain) is now widely used in artisan bakeries and is increasingly adopted in industrial settings — especially as consumer demand for "authentic" and "long-fermentation" breads grows.

6.2 Wheat sourdough targets and management

• Inoculation level: typically 15–30% of flour weight as ripe levain
• Final dough temperature: 24–26°C for standard; 22°C for overnight retard
• Final proof time: 1–4 hours at room temperature; 8–16 hours at 5–8°C (retarded)
• Target dough pH before baking: approximately 4.5–5.0
• Scoring: wheat sourdough must be scored before baking to control oven spring direction

The Puratos O-tentic range is designed specifically to simplify wheat sourdough production at commercial scale: added at 4% on flour weight with water and salt, it brings active sourdough microorganisms (from dried durum wheat sourdough) alongside yeast, ascorbic acid, and enzymes in a single dry concentrate. See Section 8.2 for detailed product data.

7. Rye vs. wheat sourdough — the fundamental difference

The single most important difference between rye and wheat sourdough is this: for rye bread, the sourdough is not optional.

Side-by-side cross-section of properly acidified rye bread (good crumb) versus under-acidified rye bread (gummy defect)

7.1 Why rye needs acid

Rye flour contains:

1. No functional gluten — rye proteins (secalin) do not form the cohesive viscoelastic network that wheat gliadin and glutenin create. The structural matrix of rye dough is provided instead by arabinoxylans (pentosans), which form a gel when hydrated.
2. High alpha-amylase activity — rye has naturally high amylase levels that are only inhibited at low pH. At the mildly acidic pH of unfermented rye dough (~5.5–6.0), alpha-amylase remains active throughout the baking process and progressively breaks down gelatinising starch — producing a wet, sticky, gummy crumb that cannot be sliced.

Acid is the technical fix for both problems:

• It crosslinks the arabinoxylans into a stable gel that holds the crumb structure in the oven.
• It inhibits alpha-amylase activity, protecting the starch network during baking.

When rye dough reaches pH 3.8–4.4, amylase activity is reduced to a safe level.

7.2 Comparative summary

See the comparison table below for the full parameter comparison.

The key practical implications are:

• For rye bread: sourdough is non-negotiable; the target acidity must be reached and verified; over-acidification (pH below 3.5) is also a fault because it degrades the pentosan gel and destroys gluten in mixed wheat-rye doughs.
• For wheat bread: sourdough improves flavour and keeping quality but is not structurally essential; the process is more forgiving of small deviations in pH.

8. Industrial sourdough products — what is in the Domson catalogue

Professional bakeries increasingly use industrial sourdough products — pre-fermented, acidified ingredients that replace or supplement a traditional starter. These fall into three categories:

8.1 Dry sourdough powders

Zeelandia Superkwas is a dry powder classified as a "wheat-rye bread improver."

• Composition: 79% rye flour, 20% acidity regulators (E330 citric acid, E270 lactic acid, E327 calcium lactate), plus traces of ascorbic acid (E300), wheat flour, enzyme, and wheat starch

• How it works: The acidity regulators provide immediate pH drop when mixed with water; the rye flour carries characteristic rye flavour compounds. This is a devitalized sourdough (no live microorganisms) — the acid is chemical, not fermented.

• Dosage: approximately 1.3% on flour weight (from application recipe: 1.3 kg per 100 kg flour)

• Process: Mixed with all other ingredients; dough temp 26–28°C; first proof ~20 min; final proof ~45 min; bake 230–250°C with steam

• Application: 70% wheat type 850 + 30% rye type 720 formula; suitable for mixed wheat-rye bread that needs sourdough flavour and acidity without a traditional fermentation step

Allergens: Contains wheat and rye (confirmed). Possible cross-contamination with barley, oat, spelt, egg, soya, milk, sesame.

Sourdough labelling note: Superkwas is a devitalized sourdough — the acidification is chemical (E330 citric acid, E270 lactic acid, E327 calcium lactate), not from live fermentation. Bread produced only with Superkwas as the sourdough component may NOT qualify for "sourdough bread" labelling in markets where this claim is restricted to products containing live-fermented sourdough (e.g. UK Trading Standards guidance, Real Bread Campaign criteria, or some EU national rules). Verify labelling compliance with a regulatory specialist before making sourdough claims on finished product.

8.2 Active sourdough concentrates (dry)

Puratos O-tentic Durum is categorised as an "active bakery component based on sourdough." Unlike devitalized powders, O-tentic contains active yeast and enzymes alongside the dried sourdough — meaning fermentation continues in the dough.

• Composition: Dried durum wheat sourdough, yeast, ascorbic acid (E300), enzymes

• Total acidity (product as supplied): 45–65 ml/10g

• Organic acids content: 5.0 g per 100 g

• Dosage: 4% on flour weight with addition of water and salt only (no additional yeast required)

• Profile: Mediterranean/durum wheat taste — designed for authentic breads such as pita-style, focaccia, and durum rolls

• Protein: 21.2 g per 100 g (high — reflects the durum wheat sourdough base)

• Storage: 16–20°C, max 65% RH, 12 months; after opening max 1 week at 0–7°C

• Dietary status: Kosher-certified; Halal-certified; vegan; GFSI-certified; NOT suitable for coeliacs

• Allergen: Wheat gluten (as ingredient); mustard (possible cross-contamination)

8.3 Paste concentrates

Uldo Dark Sauer (W/43) is a dark-brown paste concentrated rye sourdough for dark rye and wholegrain breads.

• Composition: Rye bran, water, rye flour, citric acid, lactic acid, acetic acid, barley malt
• pH range (product): 2.5–4.5
• Total acidity: 140–150 SH° — approximately 5–6 times more acidic than a typical ripe rye sour at 20–30 SH°; this is an extremely concentrated acid paste
• Dosage: 2–8% on flour weight, depending on desired acidity and rye content
• Shelf life: 9 months; store max 30°C, max 75% humidity
• Allergen: Gluten; traces possible: milk, sesame, soya, lupin, eggs

8.4 Liquid sourdoughs

Zeelandia Bioferm Ciemny is a dark-coloured liquid sourdough for mixed, rye, and wholegrain breads.

• Composition: Liquid whey, rye flour, acidity regulators (E270 lactic acid, E260 acetic acid), wholemeal rye flour, rye bran, barley malt flour, roasted barley, roasted rye, salt, pre-gelatinised wheat flour, natural bread sourdough

• pH (product): 2.4–2.8 — among the most acidic of any liquid sourdough product

• Total acidity: 250–260 SH°

• Dosage: 2.5% (50/50 rye/wheat blend) → 3.2% (70% rye) → 3.5% (80% rye) → 4% (100% rye) on flour weight

• Application: Pre-soak rye wholemeal + Bioferm in ~70% of dough water for 2–3 hours before mixing; dough temp 29–31°C; final proof ~50 min; bake 250°C falling to 200°C (60 min total)

• Shelf life: 12 months; 0–25°C, do not freeze

Critical allergen note: Bioferm Ciemny contains liquid whey as the FIRST listed ingredient — it is therefore a significant source of MILK protein. Bread produced with this product contains milk allergen and must be labelled accordingly. This is not a cross-contamination risk — whey is a declared, intentional ingredient. Verify the current spec before every batch order.

8.5 Soaked grain inclusions

Puratos Sapore Softgrain Rye is a unique product — it is rye grain soaked and cooked in natural sourdough rather than a sourdough concentrate itself.

• Composition: Fermented sprouted rye grain, pasteurised rye sourdough, salt, potassium sorbate (E202 — preservative)
• Grain content: 56g of grains and seeds per 100g product
• pH (product): 3.20–3.70
• Total acidity: 7.0–12.0 ml/10g (NaOH 0.1N)
• Dosage: 10–50% relative to dough weight (note: unusual metric — all other sourdough products in this section use % on flour weight)
• How to use: Add at the beginning or end of mixing; cannot be frozen; refrigerate after opening at 0–4°C for maximum 2 weeks
• Nutritional note: High fibre (6.6 g/100g); moderate energy (143 kcal/100g)
• Allergen: Cereals containing gluten (rye — as ingredient and on same production line)
• Quality: BRC Global Standard Grade AA

E202 (potassium sorbate) carry-over — regulatory note: Sapore Softgrain Rye contains E202 (potassium sorbate) as a preservative. At 10–50% dosage on dough weight, E202 will be present in the finished bread above a technologically insignificant level. In the EU, sorbates are NOT authorised in standard bread (Category 07.1.1 under EU Regulation 1333/2008 Annex II). For fine bakery wares (Category 07.2) sorbates are permitted at a maximum of 2000 mg/kg in the finished product. Before using Sapore Softgrain Rye in standard bread formulations at significant levels: (1) identify the correct EU food category for the finished product; (2) calculate the actual E202 carry-over concentration; (3) obtain Puratos' regulatory compliance documentation for your market.

Sapore Softgrain Rye is primarily a texture and flavour inclusion — the soaked, fermented grains add chewiness, visual texture, and sourdough character to bread doughs without replacing a traditional sourdough fermentation step.

See the comparison table below for a full side-by-side comparison of all five products.

9. Fault diagnosis and remedy

See the fault-finding table below for the complete list. The most critical faults in sourdough production and their sourdough-specific causes:

Note on mould inhibition and E282 (calcium propionate): E282 is NOT permitted in standard bread (EU Regulation 1333/2008 Annex II, Category 07.1.1 — bread made only with wheat flour, water, yeast/leavening, and salt). It IS permitted in pre-packed sliced bread (Category 07.1.2) and fine bakery wares (Category 07.2) at a maximum of 3000 mg/kg in the finished product. Before adding E282 to any sourdough bread formulation: (1) confirm the correct EU food category for your finished product; (2) verify compliance with the applicable national implementation; (3) do not use E282 if the product is standard bread (07.1.1). E282 works synergistically with sourdough acidity and is most effective at pH below 5.5 — which sourdough already achieves.

10. Choosing a sourdough approach for your production

Coverage notes and gaps

Solid coverage in this dossier:

• Sourdough microbiology — LAB:yeast ratio, species, synergy (academic PMC source + IREKS Compendium)
• Acidification principles — pH curve, lactic/acetic balance parameters
• Multi-stage Detmold rye processes (IREKS Compendium — the industry standard reference)
• Industrial sourdough product data from five first-party spec sheets
• Fault table from an IREKS Compendium fault source

Thin or uncertain areas:

• Exact target pH range for rye doughs (3.8–4.4 is indicative from IREKS; confirm against specific flour enzyme activity for each production run)
• Starter refresh ratios are common professional practice; no single authoritative source states specific ratios; marked confidence:medium
• Böcker product range (Bio Le Chef, Flüssigsauer 200, Reinzucht starter) — no readable spec sheets available in the catalogue (PDF mismatch for Le Chef); product details from brand sources only
• Long-term effects of sourdough on bread nutrition (phytate reduction, GI) — mentioned but not developed; these claims require medical nutrition review
• EU/UK regulatory status of specific sourdough label claims ("made with sourdough", "genuine sourdough") — not addressed here; a Zeelandia sourdough labelling compliance source notes this is a topic; requires regulatory review