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Yeast and Sourdough, a Lesaffre Expertise

Historical background

Yeast and sourdough have historically lived side by side in the world since ancient times, undergoing periods of preferential use, especially in western countries. In France, sourdough and yeast were used alternatively until the late seventeenth century, and then for different purposes until 1840: yeast in poolish (liquid sponge) for high-quality bread and sourdough for more common products. It was not until the late 1940s that the use of yeast was generalized, while sourdough regained popularity amongst the bakers from 2000.

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Yeast and sourdough serving fermentation

Yeast and sourdough are both fermentative agents destined to make dough rise as a result of carbon dioxide production. Both also contribute to the development of the bread’s aromas.

Sourdough is associated with long fermentation practices and the resulting products demonstrate strongly typed flavor profiles. These characteristic flavors are generated by the production of organic acids, mainly acetic and lactic acids. The impact on rheology is special: it results in a lower specific volume and a thicker crust. The lower pH increases bread shelf life via an anti-fungal effect, and bread staling is slowed down by a reduction of the speed of starch retrogradation.

It was Louis Pasteur who demonstrated the role of yeast (Saccharomyces cerevisiae) in what was until 1857 the “mystery” of fermentation. Since then yeasts, just like sourdough bacteria, have been isolated, propagated and concentrated, even assembled. Bakers now have selective ferments, stabilized and concentrated.

The microorganisms they contain provide fermentative activities and aromatic profiles that are no longer haphazard but controlled. Their activity is standardized, so it is easy to use in baking whatever the environment. Far from being opposed to each other, sourdough and yeast are therefore complementary and now reunited for a better regulation of fermentation activity and a stronger aromatic signature.

The management of these microorganisms (yeast and bacteria) is essential for those who want to offer unique fermentative and aromatic solutions.

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Scientific understanding of strains, a key element in the fermentation process

The genome sequencing of Saccharomyces cerevisiae is a relatively recent approach (1994-1997) which enabled a better understanding by differentiating and categorizing the available strains according to their profiles and properties. Global coverage and the mastering of strain isolation thus enables us to select the most promising yeast and bacteria for pure or combined use.

In recent years, the development of screening techniques enabled the filtering and selection of candidates showing the strongest potential regarding specific properties. These include the fermentation rate (also called kinetics), aromatic properties, resistance to osmotic pressure, salts and acids.

These candidates are propagated at the pilot scale in order to study their ability to reproduce for future industrialization and confirm the expected performances in baking applications. Finally, the combination of these microorganisms enables us to offer both ready-to-use and customized solutions.

Instead of storing cocktails of bacteria issued from multiple sources of stabilized sourdoughs, it is now possible and advisable to isolate and multiply the selected microorganisms. They can then be reassembled as needed to take advantage of the wealth of the planet in terms of biodiversity, be propagated freely and thus shared. One more way to become independent from a skill or an exclusive and variable environment. Stored at -80°C the ferments (yeast and bacteria) will be preserved in special conditions, then bred to be available to production sites.

Being able to control the fermentation chain in its entirety, from the selection of the strain to the sensory analysis of the baked products, is an asset that only a few actors on the market can claim to. This gives them a consolidated view and exceptional responsiveness at the service of their clients.

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Integrating local specificities and technologies

Understanding microorganisms, yeasts as well as bacteria, knowing how to multiply them in secure and environmentally friendly conditions is necessary but not enough. It is important today to understand and integrate local specificities.

The type of flour substrates (wheat, rye, buckwheat, etc.) and ingredients used (sugar, growth inhibitors, etc.) play a critical role during fermentation. They led yeast producers to develop the appropriate strains: yeast for acid dough using rye flour, osmotolerant yeast for high sugar dough.

The type of process and fermentation (short, long, blocked,frozen and sponge & dough) pushed manufacturers to provide increasingly customized fermentation solutions. Recent developments include fast kinetics yeasts (short diagrams, Anglo-Saxon profiles, also called “high activity”) and yeasts sensitive to cold. The latter enable a temporary blocking of fermentation to ensure flexibility in work organization or movement of semi-finished product to baking terminals. They also allow selling ready-to-use chilled dough to households. Originally used for other types of fermentations, some yeast such as maltose-negative are now applied to bread-making. This kind of yeast which cannot assimilate the maltose substrate of the flour has a limited action in time: an ideal solution to stabilize dough at room temperature.

Applications (crusty bread, sweet bread, sweet goods, pizzas, steamed bread, Arabic bread, etc.) are also decisive in the choice of fermenting agents.

The same applies to desired effects (customized aromatic signature, mild or intense, shelf life, etc.) that guide research on sourdough, alone or in combination with yeasts: a search for symbiosis between a yeast strain and bacteria for “dual effect” sourdough.

The conditions of preparation have largely orientated developments in the field of sourdough: refreshments and development of the pre-ferment before inoculation into the final dough, a desire to separate flavoring and fermentation properties (use of deactivated sourdough in combination with yeast), direct incorporation (ready-to-use living sourdough), etc.

Logistical constraints (accessibility, mean consumption, changes in production rates, etc.) influence the final stabilization of the sourdough, and are critical variables taken into account in the development of different yeast forms: liquid ready-to-use, ideally suited for automatic dosing (solutions for industrial but also craft bakers), compressed (in block or crumbled), dried (ready-to-use or to rehydrate before incorporation in the dough), frozen (Frozen Yeast of Intermediate Humidity for frozen dough).

It is through their ability to appreciate global issues and adapt them to a local or individual scale, that some actors are able to develop the most effective solutions.

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Steamed Buns, a Lesaffre Expertise

Like China itself, mantou has an age-old history steeped in legends and symbols and has evolved over time with the Chinese people

The history of mantou is closely linked with the Three Kingdoms Period (AD 220-280). Strategist, Zhu Geliang, is said to have led the armies of Shu in the south Campaign, and, after defeating King Meng Huo, he came across a fast-flowing river on his way back. Local barbarians told him that the river spirits could be appeased by the sacrifice of 50 men, each of whom would have their heads cut off and thrown into the river. Exhausted by the campaign and proud of the low number of casualties, Zhu Geliang therefore decided to fake the men’s heads by stuffing some dough balls with meat and throwing them into the river. As the waters of the river grew calm, he and his army were able to cross. The meat-filled dough balls thus became known as “Barbarian heads” or mantou in Chinese.

The first known uses of sodium bicarbonate in steamed buns date back to 1206. The steamed bun was the only type of bread eaten in Asia until 1866, the year in which the first European buns (mianbao 面包/麵包) were introduced into the country, mainly via Hong Kong and Guangzhou. In 1970 yeast was imported into the Guangzhou region for the first time to replace the traditional sourdough (laomian 老面/老麵). The first local yeast factory (Danbaoli 丹宝利/丹寶利) was built in Guangdong in 1985.

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A product particularly well suited to Asia and its production, environment, and consumption demands

Historically and culturally, mantou is a staple in northern China, as a main source of protein, especially in the grain-producing Shandong province. The northern mantou is eaten with all 3 meals of the day. Consisting of only flour, water, and a fermentation agent (yeast or traditional sourdough), an alkali (baking soda, i.e. sodium bicarbonate) is often added to neutralize the pH created by the lactic ferments, to lessen the sour taste of the finished product. It is typically white, round, and ball- or cylinder-shaped, with a smooth, even surface. It has a dense, elastic, grainy texture and weighs between 50 and 150g.

The southern mantou is a traditional product (snack or dessert) that supplements rice, the main staple crop grown in southern China. The southern mantou often has a sweet taste, 5 to 20% sugar to the weight of flour, sometimes with a trace of salt and shortening, and is usually softer than its northern counterpart.

Mantou, in its northern and southern variations, belongs to the steamed bun family, which clearly differs from other western bread families in its production method and in the end-product itself: steaming (at high humidity and a temperature of no more than 100°C) does not allow browning or the release of associated aromas to occur, since the temperature required to generate the famous Maillard reactions and caramelization is never reached. Unlike European bread, mantou has no crust or experience a loss of weight through evaporation during baking. The resultant steamed bun is soft, smooth and white.

Mantou is eaten hot, after steaming or reheating, in individual portions. The main evaluation criteria are as follows:

  • Appearance: must be smooth and even, white in the north, a slightly creamy color in the south, shiny, consistent (i.e. symmetrical, not wrinkled, blistered, or patchy).
  • Texture: should be dense in the northern mantou, slightly more aerated in the southern version. The crumb should be fine, consistent, elastic, chewy (not sticky), and more aerated in the south.
  • Aroma and taste: these should be natural, if not neutral (especially in the case of the northern mantou), expressing the ingredients used for the dough or the fillings; the fillings can be sweet (azuki bean, custard cream, black sesame seeds) or savory (vegetables, meat, seafood).

A simple recipe, but a high-tech product

The basic ingredients for a mantou are flour, water, and a fermentation agent. These may be enriched with sugar, salt, and shortening for the southern mantou (nanfang mantou), and even stuffed (many types according to a secret recipe) in the case of the baotzi (包子).

The flour used is always a wheat flour with a low ash content (0.35 to 0.55%) and thereby results in a white color with no speckling. The protein level is medium to low with a consistency profile yielding an elastic dough (little or no extensibility) with high tenacity. The flour is increasingly corrected to guarantee constant regularity, despite the ever-changing grain quality, and to make it especially suited to mantou production (machinability and impact on finished product). The falling number (FN) is often over 300 and the damaged starch rate is below 8% (in excess, it can result in stickiness and speed up starch retrogradation). Moisture content is quite low at around 40 to 55%, depending on the flour (protein level, damaged starch content). The dough is therefore stiff and the lamination stage is crucial in the dough’s development.

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The fermentation agent can be sourdough or yeast (or indeed both, as in a yeast-based dough left to rest and ferment for a day or more). The traditional fermentation agent is laomian, which is often prepared in a liquid form based on rice or fruit; the micro- organism fermentation culture is mainly wild yeasts and lactic bacteria, hence the high acidity of the dough created during the process. In order to neutralize the low pH, baking soda or a similar alkali is commonly added in moderate doses to prevent yellowing and a strong soda flavor. Yeast tends to replace these sourdoughs for its ability to control activity and taste and make the end product more consistent. Compressed yeast or instant dry yeast can be used, with a low-sugar profile being common in the northern mantou and a high- sugar profile in the sweet mantou and baotzi.

  • Other raising agents can include: baking powder for obtaining “oven spring.”
  • Other ingredients include: salt for taste and shelf-life, sugar for taste and texture, shortening for taste, as well as texture and shelf-life.
  • Improvers/correctors can include: oxidants (generally ascorbic acid); enzymes for the consistency, machinability, gas retention and finished characteristics, such as volume and texture; emulsifiers for gas retention, texture and shelf-life; and preservatives.

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A traditional, yet increasingly controlled process

There are two ways of making steamed buns: the traditional way and the direct method. The traditional method aims to develop the aroma, limit the use of yeast, improve dough working and the finished product characteristics by means of a long process (and often not easily reproducible). An initial dough is made with yeast and incorporated after a day of “free” fermentation into another dough (10 to 50%), often the main dough of the day before. Another method would be to make a starter culture, which is refreshed several times in order to increase the bacteria population, then incorporated into the main dough (this kind of sourdough is called laomian).

The direct method is based on a much shorter process (1 to 3 hours) with the use of yeast and allows better control over taste consistency and fermentation activity. It yields a better-looking and more consistent end product, but also gives a more neutral taste and a shorter shelf-life. This method is widely used in automated production, which has boomed in recent years.

The automation of production methods goes hand-in-hand with the increasing requirements governing raw materials: more specific flours (grinding process, flour blends, flour improvers), yeast with very constant performance and stability over time, and specially formulated improvers. Automation, reduced production time and the increase in hourly volume all make higher demands on raw materials in order to prevent variations on the production line at inspection points. Meanwhile, equipment has also changed enormously. It started out by reproducing human gestures, but is now more specific, offering line laminating, continuous filling, automated tray loading, etc. The concentration of production sites has also meant that products must have a longer shelf-life and to be able to travel longer distances, in order to reach catchment areas and meet distribution demands. Freezing technology and new packaging techniques (i.e. modified atmosphere) have also contributed a great deal to these developments.

Using either method, the products can then be sold directly (after steaming), kept hot and moist inside bamboo boxes with steam generated from below, and kept fresh to be subsequently reheated, or frozen (after being fully steamed).

Mantou, a product of the past with a great future

Culturally, mantou is a product that has enjoyed a long and rich history, yet it has a bright future ahead of it due to the following:

  • Nutritional value: rich in slow-burning carbohydrates, contains a fair amount of proteins, low lipid content; it is also a source of some vitamins and minerals.
  • Presentation: adapted to the increasingly nomadic working lives of people looking for a ready-to-eat product (no equipment, no cutlery or other constraints), pre-packed in individual portions, easy to personalize (shaping and filling), easily accessible (mantou makers are popping up everywhere), very fresh.
  • Production method: enables the concept to be adapted to ‘hot corners’ thanks to centralized production: concentration of human, technical and financial resources on the same site, with easy access to transportation. The products are then extra fresh all day long, easily reheated and losses due to unsold products are limited. These spots are typically small: minimal or no storage area, no need for heavy goods vehicle access, power, and safety constraints (baking).

Extending the Shelf Life of Bread

View of our Baking Expert for North America

By Arnaud Deniad, Lesaffre Yeast Corporation

Preserving food products is now a strategic challenge for food industries, especially in the baking segment. In this  challenge there are threeimportant points to consider:

Health
The product must reach the consumer healthy and uncontaminated, as well as free from any prohibited preservative substances.

Techniques
Preservation measures have an impact on strategy and the choice of distribution networks, and also directly on production costs. Being able to control and extend the preservation of products, means being able to conduct our operations on large-scale sites (thereby concentrating human and technical resources), ensure greater flexibility in the face of logistical and production constraints, reduce fixed costs, acquire more productive lines and reduce time spent on formula changes. Controlling shelf life should not just be confined to the finished product, but should also factor in the possibility of introducing stabilization phases for semi-finished products when inhibiting fermentation with positive or negative cold temperatures, produced in series (shaped or not shaped, raw or pre-baked) and finished products throughout the consumption process, including consumer purchase or customer orders. This means little wastage, a broad range offering, little or no stock outages, and products that reach the customer “ultra fresh”.

Sales
A longer shelf life permits the exportation and production of larger series. The possibility of distributing finished or semi-finished products to larger catchment areas increases customer outreach (quantitative advantage) with better quality products: qualitative advantage -> organoleptic quality in terms of smell/flavor/texture as well as nutritional quality. Shelf life is a powerful competitive factor when it comes to intermediate customers (out-of-home catering) and distributors (large and medium supermarkets) for greater flexibility and reduction in the number of removals of products having exceeded their use-by date (5 to 50 percent of bread produced is never eaten!).

The question of prolonging a loaf’s shelf life is not a conceptual question nowadays, but a crucial one: should I extend my bakery or build another one closer to my clientele? Should I prioritize the productivity and flexibility of my production equipment?

In truth, the larger the country and the greater the consumption, the stronger the impact of such a decision. For several years, our customers have been asking us to take part in the debate on this issue and offer solutions that will enable them to preserve/prolong the quality of their products: as a result we have acquired a broad experience with yeast fermentation agents (special yeasts for long-life bread, yeast for frozen applications, yeast for cold-controlled fermentation, etc.) and sourdough, technical improvers (soft, fiber-rich).

View of our Expert in Microbiology, Fermentation Agents, and Bakery Products

By Renaud Toussaint, Lesaffre R&D Department

The factors promoting the deterioration of a food product are essentially the following:

pH
From a microbiological point of view, the optimum pH for mold growth is somewhere between pH 2 and 9. Controlling the pH can decelerate microbe development or inhibit it at a very low pH. From a preservation point of view, the pH will influence the deterioration in texture, which will help to increase firmness. Controlling the pH of a loaf will have noticeable organoleptic consequences: taste, crumb consistency/chewiness, color.

Temperature
The optimum temperature for microbial development is somewhere between 59°F and 86°F (15°C and 30° C) for mold with a risk of toxin production in the event of over-contamination by mold (that cannot be neutralized by temperate control). Staling is influenced on 3 levels:

  • 86°F to -4°F (30°C to -20 °C)
    Stabilization occurs, no development
  • -4°F to 20°F (-20°C to – 7°C)
    Low/slow development
  • 20°F to 50°F (-7°C to 10 °C)
    Rapid development, a critical phase between 26°F and 41°F (-3°C and 5°C)

Shelf-Life-Biospringer

Oxygen
this factor conditions the development of aerobic flora (which needs oxygen to thrive), especially mold , but it is also an oxidizing factor for bread and fat-rich Viennese pastries (rancidity and appearance of off-notes in finished products).

Humidity
Related to both the product and the environment, generally speaking, the higher the rate of humidity (expressed as ‘free’ water), the greater or sooner the risk of microbial development. The rate of humidity after cooling directly impacts the softness of the product after manufacture, but also during its preservation, the corollary being that excess humidity promotes the development of mold in hermetic packaging.

Hygiene
Related to conditions during production including separation of flows, atmosphere control (air filtration etc.), the relevance of cleaning (solutions used/mechanical and thermal effects frequency, etc.) and effective and exhaustive application thereof.

Contamination of raw materials
Notably flour (preservation of wheat, extraction, etc.) and inclusions (seeds, etc.).

Human factor
Error, oversight, lack of attention.

Our thorough knowledge and understanding of these mechanisms have helped us to help customers choose and control their formulae (recipes), set the correct parameters for their facilities (T°, humidity, etc.) in conjunction with our range of the most suitable yeasts and correctors.

View of our Quality Expert

By Si Jingran, Director of Hygiene & Quality, Lesaffre China

It’s difficult to produce an exhaustive list of preservation methods since there are so many and some are specific to certain products (smoking and immersion methods are not compatible, for instance, with bakery goods).

Some historic techniques are still in use (smoking, acidification, etc.), other techniques are more recent (irradiation or microfiltration). Some are deliberately sought out and researched and others are the result of a stage introduced for other purposes (e.g. baking in breadmaking is not chiefly aimed at decontamination and it is not controlled as a function of this parameter).

Some methods will alter the sensory aspects of the product in question: taste (i.e. sourdough or acidification), smell (i.e. Calpro, brine curing, etc.), others not (irradiation, microfiltration of water).

Shelf-Life-North-America

A rapid overview of the main food preservation techniques (in general) highlights the following methods in use:

Baking
By definition, baking is a destructive process for heat-sensitive flora as of 55°C (bacteria, yeast, mold ). However, there is such a thing as heat-resistant flora, e.g. Bacillus subtilis or Bacillus mesenteric us, both responsible for ropey bread.

Acidification
Through the addition of sourdough or an acidifier. This treatment is more strongly recommended in the case of ropey bread (combined with in-depth cleaning of the work environment).

Microfiltration
especially with water or air in “white” rooms or cooling rooms in particular.

Organic environment
spraying with yeast or bacteria and/or ambient/resident flora.

Temperature control
through the use of positive cold (retarded dough or inhibited fermentation methods) or negative cold (freezing).

Immersion
which permits the preservation of ingredients that can be incorporated into bread (olives in brine, anchovies in oil, pickled vegetables, etc.) but not bread as such.

Irradiation by UV treatment
Used for bread packaging, water, and air (UV lamps in fermentation chambers to prevent mold growth) or by infrared.

High-tech packaging
Through the use of materials (watertight film, oxygen, etc.), gas (blanketing by N/CO2) or atmosphere regulators (O2/damp absorbers).

AW control
Through concentration, drying (baking and crisp baked principle), salting, sugaring (brioche, panettone, etc.).

Use of additives
Preservative agents and anti-staling agents (including enzymes). Chemical preservatives for microbiological control (mainly calcium propionate, benzoate/DHA in certain applications. Emulsifiers for instant and long-term softness (SSL, Mono, CSL, etc.). Alcohol (in special formulations or by spraying during cooling). Fermented flour. Enzymes, mainly anti-staling enzymes acting on the retrogradation of starches and which impact on crumb firmness and elasticity.

Choice of raw ingredients
Wheat (chemical and bacteriological contamination), flour with low extraction rate,
pure ferments (yeast).

Control over a product’s shelf life is rarely the result of action taken on one of these parameters, but often a combination of several.

View of our Baking Expert in Asia

By Thomas Kalkhoven

Our technical support mission and our world coverage have led us to work in collaboration with many players in the profession: enzyme manufacturers, emulsifier producers, millers, etc., in numerous applications i.e. crusted bread, sweet bread, flatbread, steamed bread, and with customers of all sizes (local craft bakers or international groups).

With these assets, we are able to capitalize on our experience. Controlling the shelf life of bakery products is indeed a major concern, compelling us to work on different solutions depending on the environment (regulatory, usage, regional bread, desired preservation time, possibility of stabilizing the product during the course of manufacture with final baking off provided on the same site or at retail outlets.

Shelf-Life-Asia

We note that the most commonly found levers in breadmaking are structured around the following 4 factors:

Recipe adaptation

  • Selection of raw materials for better control over the aW of raw materials or improve the properties of the end product (use of boiled flour to increase hydration resulting in a rise in initial softness, steaming, etc.).
  • Adjustment in levels of hydration and/or use of a hydrating agent (fiber), or humectant (sorbitol, mannitol, glycerol, etc.), hydrocolloids (carob flour (E410), Guar flour (E412), carboxymethylcellulose (E466)).
  • Use of enzymes with preservation/softness/anti-staling properties.
  • Use of acidifying sourdough or pH regulators (acetic acid, citrates, tartrates, phosphates, carbonates, etc.).
  • Use of tensio-active ingredients: Mono & diglycerides (MGL – E471); sorbitol/ glycol esters – polysorbate (E435); lactic acid derivatives (SSL E481 – CSL E482); sorbic acid and sorbates; propionic acid and propionates (sodium, potassium, etc.).
  • Use of preservatives: ethanol; antibiotics (N.B. prohibited in bread in most countries); antifungal agents: sodium diacetate/dehydroacetate, propionic acid and propionates (calcium, potassium, etc.), sorbic acid and sorbates, etc.)
  • Use of boiled flour.

Adaptation of manufacturing Processes

  • Mixing: including gas dough release rate.
  • Fermentation: ferment used (sourdough, yeast, etc.), process (sponge & dough/long fermentation/fermentation conditions (duration, T°) and environment (hygrometry).
  • Baking: drying out, thickness of crust, etc.
  • Cooling conditions: duration, T°, air circulation rate, tools, purity of atmosphere, etc.
  • Environment control throughout the process, on all materials in contact: equipment and small utensils, atmosphere.

Intermediate and final stabilization

  • Inhibition or slowing of contamination in intermediate phases using cold temperatures (positive or negative cold) depending on the desired stabilization period, or finished products.
  • Modified atmosphere: neutral gas and vacuum preservation in the end product.
  • Use of packaging materials with regulating properties (humidity, air, etc.)

Decontamination

  • Raw ingredients: heat-treated flour, UV treatment of packaging materials, air filtration, water microfiltration, etc.
  • Facilities: cleaning and disinfection of premises, equipment and small tools, UV radiation in fermentation chamber, etc.
  • Finished products: spraying with alcohol-based solutions, yeast.

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