Bakers are experimenting with different strains of yeast and fermentation times to achieve signature flavours… and there may be opportunities yet to tap.

Ancient Egyptians were no strangers to using yeast in baking, but it wasn’t until the 19th century that scientists started to understand how this microorganism works its magic.

In baking, yeast ferments the sugars in dough to produce carbon dioxide, which makes the dough rise. But fermentation also produces other by-products, some of which are lost during baking but many of which contribute to the flavour of the bread.

“It is estimated there are more than 540 different aromatic compounds in a slice of bread,” explains Lesaffre technical manager Sara Autton. “Yeasts generate different families of aromatic compounds that give specific tastes: ketones (buttery, caramel notes), esters (fruity, spicy, vegetable notes), alcohols (floral notes) and terpenes (ripe wheat, woody, spicy notes). Furthermore, yeasts add their own flavour depending on the usage rate and the type used.”

The flavour of a bread can be affected by altering the length and temperature of the fermentation process. Flavour molecules produced by yeast can also be varied by the type of flour, the kneading and water content, says Lallemand sales director Sean Quinn.

“By playing around with these parameters, including the type and quantity of baker’s yeast used, it is possible to bake with your own signature,” he adds. “For example, with retarded proofing conditions, a lower amount of yeast can be used without compromising the flavours.”

Some suppliers offer yeasts designed to impart different flavours, with Lallemand producing Florapan aromatic yeasts made from strains of wine and beer yeasts. These are used with, or in place of, conventional baker’s yeast with a pre-ferment step or extended proof time to enhance the aroma.

Lesaffre, meanwhile, supplies yeasts with different fermentation rates, including an osmotolerant yeast for use in enriched products, such as brioches, to ensure a buttery flavour dominates.

Campden BRI is planning to study how different yeasts contribute to the flavour of bread, and hopes this will lead to a project co-funded by interested companies to take this research further.

“The challenges are around adequacy of gas generation for proof times, flavour generation and checking for potential for toxic metabolites,” said a Campden BRI spokesperson. “There is also evidence that different yeast strains could help improve the mould-free shelf life of baked goods.”

Craft bakers are experimenting with different yeasts, including standard baker’s yeast and some distillers yeast or wine yeasts, explains Sam Cook, marketing business partner at AB Mauri UK & Ireland. “This is either as fresh or dried yeast, and either as a blend or as a pure culture of different yeasts, to create unique flavours and differentiate themselves in the market.”

Meanwhile, Quinn recommends special strains of baker’s yeast are used for sweet doughs and those to be frozen or refrigerated. “For example, when up to 30% sugar is added, this creates a high osmotic pressure that can affect yeast’s fermentation rate,” he explains. “And the low temperatures used during freezing generally decrease dough leavening due to an overall loss of yeast viability, which ultimately leads to a significant decrease in final quality.”

Further developments in yeast, driven by market demands, could include strains that will improve the nutritional value and digestibility of bread. “New bread-making methods, processes and equipment may well demand yeasts with different activities,” says Autton. “Research and development in yeast fermentation may also discover yeast types with activities that are, as yet, untapped, affording exciting opportunities for new product and process developments.”

Different takes on culture

There’s no role for commercial baker’s yeast in a sourdough loaf, according to the Real Bread Campaign.

The group is campaigning for a legal definition of sourdough, arguing the term should apply only to bread made with a live sourdough culture, and not inactive dried sourdough powder, commercial yeast or other leavening agents.

But ingredients suppliers argue there is a place in the modern bakery market for loaves containing sourdough and commercial yeasts, helping a wider range of businesses tap the burgeoning consumer interest in sourdough.

Lesaffre, for example, offers the Livendo range of cultures, ready-to-use living levains and devitalised dry products. And Lallemand’s Florapan range includes baking cultures that produce a ready-to-use levain in 18 to 24 hours at temperatures between 20°C and 35°C.

Lesaffre technical manager Sara Autton acknowledges the “growing movement to protect the integrity of sourdough as a traditional method of bread-making”, but contends that there is also a place for bread that uses sourdough in conjunction with ‘baker’s yeast’ to create different textures and flavours that some consumers may prefer.

“To deny the opportunity for innovation that this dual fermentation approach allows would diminish the scope of product development,” she says.

Breads made with 100% bacterial sourdoughs will have a balanced lactic-acetic flavour profile that keeps naturally well for a longer period of time, explains Lallemand sales director Sean Quinn. He adds, however, that without yeast, there will be limited carbon dioxide production, and the bread will be flat.

“To have the best of both worlds, and conditions that probably reflect more the natural microflora of flour and the bakery environment, sourdoughs made from lactic acid bacteria and aromatic yeast are ideal,” he says.

Although interest in sourdough bread shows no sign of waning, it is still a niche market among mainstream bread styles. Autton concludes: “The sourdough alternative is gaining ground, but unless consumers fall out of love with the soft, springy texture of bread made with yeast, then both will have a place in the market for a long time to come.”