Creating a sourdough ‘starter’ – which involves developing your own yeast culture rather than adding yeast to the mix – entails mixing flour, water, and other ingredients that have been colonised by wild airborne bacteria. A sourdough starter contains a strain of yeast that is tolerant of the lactic and acetic acids produced by the lactobacilli, giving the bread its unique tang. For bakers considering developing their own starter, the best tip for a successful sourdough is to reduce the risk of microbial contamination from other sources as much as possible. The conditions in a mother dough need to be controlled to ensure the continued reproduction of yeast cells. If the dough becomes contaminated with other micro-organisms – yeasts, moulds and bacteria – and the storage conditions favour those micro-organisms rather than the yeast (all micro-organisms have their own favoured food and growth conditions controlled by temperature and pH), then development of ‘off flavours’ and loss of performance can become a real problem. Here are Dan Lepard’s top tips for better sourdoughs Start with an active, bubbling, acidic leaven mixed with equal quantities of flour and water, without the addition of commercial yeast. 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.