Take the strain

03 February, 2006
With sourdoughs back in vogue, bakers are searching for new yeast strains. Andrew Williams discovers an excellent source
Page 21 
For those with long memories who think bakers ‘don’t make bread like they used to’, the loss of the hearty, flavoursome recipes of pre-war breadmaking are sorely missed. The impact of new manufacturing processes and ingredients on the quality of bread since the 1960s is well-documented. But what of the changing role of yeast in bread flavour?
Yeast production has become an exact science, but many bakers once turned to their local brewery as a source of yeast. “Before the war a lot of bakeries would have been using yeast they obtained from the local brewery,” says Dr Ian Roberts, curator of the National Collection of Yeast Cultures (NCYC). “There is interest in recreating these kinds of breads using traditional yeasts and our brewing collection might be a source of novel diversity for that sort of activity.”The yeast archive, based at the Institute of Food Research, Norwich, maintains only a small number of baking strains and associated information at present. These are available to bakers on request, but the majority of cultures stored from the brewing industry, that have fallen out of use, could also provide a handy resource for bakers.“There has been recent interest from bakers looking at using early yeast strains tore-create breads baked in Britain prior to 1945, or to check their current yeast strains using state-of-the-art molecular characterisation technology,” says Dr Roberts of therecently re-launched collection.The NCYC was founded in the late 1940s and some yeasts held there go back to the early part of last century. The yeasts in a sourdough undergo a complex interaction with different strains of bacteria and the sugars released by the bacteria are likely to be responsible for initiating fermentation, says Dr Roberts. This complex interaction will influence the bread’s taste, texture and shelf-life.“It’s hard to be precise about whether flavours originate from the bacteria, the yeast or the combination,” comments Dr Roberts. “NCYC can, however, tell precisely what’s there and how different it is from other strains from the same yeast species.”Global variationsSaccharomyces cerevisiae, Saccharomyces exiguus, Torulopsis holmii, Candida humilis, Candida holmii, and Candida milleri. This is not a slip on the keyboard, but the names of yeast species that have been identified in sourdoughs, which vary in strain around the world.“NCYC staff have experimented with sourdough recipes involving Californian raisins,” Dr Roberts explains. “They found several yeast types might contribute to the final product. We have the capability to isolate them all and perform precision identification, storage and strain tracking using techniques of molecular biology. We could certainly isolate the yeast, characterise it, compare it with our other strains and store it as a pure culture.”The collection is in the public domain and a strain of yeast could be supplied at £70 per culture. “We would talk bakers through it and try to provide some assistance in selecting yeasts,” he says.NCYC also offers bakers the opportunity to identify and catalogue their own yeast strains, such as those developed with their signature sourdough starter. They can then safely deposit them, as the brewing and the food industry do, and the information gleaned can be used to develop products.For large-scale manufacturers, the delivery of yeast into the breadmaking process is a precise science. Yeasts are used in biotechnology to produce proteins, flavours, vitamins and functional foods. Genetic research into yeasts may also develop designer yeasts with new commercially valuable characteristics, says Dr Roberts. But perhaps the chance to resurrect breads from a bygone era could be more appealing than the Brave New World.For more information see: www.ncyc.co.uk Which commercial yeast do you need?Block Yeast: This is particularly suitable for no-time doughs such as those mixed on spiral or high-speed mixers.Traditional fresh block yeast: Ideal for doughs with longer fermentation times. Traditional yeast produces carbon dioxide at a lower rate than block yeast and provides the baker with greater tolerance to process fluctuations. Traditional yeast is often the best choice for craft bakers or in-store bakeries.Cream yeast: For the industrial baker, this yeast is supplied in liquid form by a road tanker. On arrival at the bakery, it is dispensed into a cream yeast storage installation. Cream yeast offers the plant baker the advantages of improved hygiene, more consistent gassing, automated dosing for improved accuracy and the elimination ofhand-weighing.Dan Lepard’s top tips for better sourdoughsStart with an active, bubbling, acidic leaven mixed with equal quantities of flour and water, without the addition of commercial yeast, writes bakery consultant Dan Lepard.Starter: Every 24 hours you should hold back one-fifth and replace what was used in baking with fresh flour and water stirred in well. Regular replenishment with flour and water is essential as it is a living thing that will respond to regular rather than intermittent feeding. The acidity will ensure that the mixture stays hostile to bad bacteria and other organisms, and will keep it fresh tasting and healthy.Recipe & method: Add 30-40% active leaven to flour weight and water to take the dough moisture percentage to 65-70% (allow for the flour and water in the sourdough). Mix and then wait. Extend the bulk fermentation until you can see clear signs of fermentation in the dough and only then divide and shape.Time: You might find that you want to chill the dough between shifts to slow down the fermentation, as it is no good if the dough ripens when there is nobody in the bakery to scale and shape it. Equally, if it is looking a bit sluggish then you might want to increase the amount of leaven in the dough. Some bakers take the percentage up to 60-70% to create a big sour tang to the crumb.Proving: With sourdough or other naturally leavened breads everything takes longer. So bakers often use a soft dough to encourage the fermentation, but this tends to flow if left on a tray. So some sort of containment, like flour-dusted baskets or cloths, that trap the dough and force it upwards rather than outwards, is needed. It will need a deft hand to quickly upturn and roll the proved fragile dough onto a peel without degassing it, then to slash it quickly without it deflating. But it is just knack, not a tricky skill.Strong flours: The longer the fermentation, the better strong flour will perform. The lightest loaves will come from strong white flour, but sometimes the flavour is a bit thin. So try using 70% strong white flour, 20% wholemeal flour and 10% dark rye flour for a big flavour and a relatively light loaf.



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