Sourdough is the most traditional way of fermenting a dough to produce bread. It has been around for the last 5000 years. It involves fermenting flour with the natural flora present in the raw material or in the surrounding air. Natural flora typically consists of lactic acid bacteria, as found in yoghurts and wild type yeasts. This mixed fermentation has a huge effect on the complexity of the bread’s flavour. The main challenge with this traditional fermentation is the very long proofing time needed; it takes up to 24 hours to leaven the dough and develop the flavour. On the other hand, baker’s yeast was invented in the late 19th century through the work of Louis Pasteur. It allowed a very high gas-producing single cell baker’s yeast to be selected and grown on a sugar-containing substance (quite often molasses). At the end of this fermentation, the yeast was harvested and added at around 2-3% in the dough. This allowed the baker to gain a lot of time. It suddenly meant that dough could be leavened in less than two hours, and always in a uniform way. The short proofing times and high consistency led to the industrialisation of bread production. Unfortunately, the flavour development is less complex compared to traditional sourdough.