Yeast Saccharomyces cerevisiae is something that we use all the time when making bread and pizza doughs. But how many of us know much about its origins?
Wild yeasts are single-celled microbes that are in the air all around us, on the leaves and the bark of trees, in the soil and on the skins of fruit. When did man first discover yeast and work out that if we added it to flour and water, it turned out a lighter loaf? How did we harness this knowledge? What does it mean for bakers today?
There are many different types of yeast in the environment, from those that cause fungal infection such as Candida to others that are used in the brewing industry and in wine-making. As we shall see there is a strong connection between bread and alcohol production.
We don't know when or how the first leavened bread occurred1; only that the first records of any sort of bread are in ancient Egyptian hieroglyphs. Possibly one day a mixture of flour meal and water was left longer than usual on a warm day and the yeasts that occur in natural contaminants of the flour - or even in milk that may have been added for flavour - began to ferment before baking. The resulting bread would have been lighter and more tasty than the normal flat, hard cake.
Gradually it became the norm to produce leavened breads, keeping a soft lump of one day's fermented dough to add to the next baking session's fresh batch to speed up fermentation. Although we mostly use commercial yeasts today, bread from a sourdough starter is not uncommon - and is more or less what the ancient Egyptians would have been baking.
In the Bible, when the Israelites left captivity in Egypt, they took their dough with them before it was leavened in their rush to depart2.
It seems likely that the next step - the interdependence between flour and yeast, bread and fermenting liquid - was established sometime later in ancient Egypt. There are hieroglyphs from over 5000 years ago which show bake-houses with dough rising next to bread ovens.
In ancient Egypt wine-making and brewing occurred alongside baking3 and it can't have taken long for some fermenting brewing liquor - a kind of liquid yeast, or barm - to have ended up in the bread dough, whether accidentally or experimentally. We just don't know. However, bread made with dough and fermenting liquid is even lighter than sourdough. So the first barm-raised bread was developed.
The Development of Science in Europe
The exact nature of yeast - where it comes from and what it is - remained a mystery for millennia. It was the invention of the microscope in the early 17th Century which finally allowed scientists to see what a single-celled yeast looked like and they soon realised that yeast cells multiply in a sugar solution, but they did not realise that they were alive. Liebig, a renowned 19th Century food chemist, claimed that it was decomposition of the cells which caused fermentation and would not accept the developing theory that yeast was a living organism.
It was Louis Pasteur who ended the mystery, in 1859, and discovered how yeast works. He established beyond doubt, using grapes, that it was the dust4 on the surface of the fruit's skin which made wine ferment, that yeast was a living organism and that only active living cells can cause fermentation.
Simply stated, the fermentation process in dough can be described as the breakdown of the starches in flour - producing carbon dioxide - which, in turn, expands the gluten proteins in the flour and causes the dough to expand. A small amount of alcohol is also produced, but this burns off as the bread bakes.
In England in the 1468 - 9 Brewers Book of Norwich, the name for barm was goddisgoode because it was made by the blessing of God. In the absence of understanding, God was invoked as the great provider.
In the 17th Century, the Paris Faculty of Medicine spent months debating whether bakers should be allowed to use beer barm for their bread. They eventually decided that it would be injurious to health, based on the fact that St Paul, in I Corinthians v, 7 signified that it was a corrupt substance. They banned it. Nobody seems to have taken much notice and bakers continued to use barm for the fine light bread that the gentry demanded. Bread made using the ancient sourdough methods remained the staple food of the masses.
Until the early years of the 19th Century, British cookery books included instructions for brewing, as well as baking, as a matter of course. Beer-making was the sole reliable source of baking yeast. The barm from wine-making tends to be very bitter and therefore rarely used for baking. Housekeepers were urged to ensure that the beer barm that they used to leaven their bread was not bitter, stale or too strongly flavoured with hops. Washing it was crucial. The quantities and quality of beer barm varied from one batch to the next, so the cookery books were unable to be specific about either. It was down to the experience of the cook to produce both a good beer and an acceptable loaf of bread.
The Commercial Production of Yeast
Yeast became more standardised when distillation of baking yeast was first developed in the mid-19th Century. This provided sufficient yeast for the rapidly-increasing population of the western European Industrial Revolution. The basis of the distillation was originally a wort, or infusion of grain, made up of wheat, rye and malted barley. Sometimes an infusion of potatoes and sugar was used5.
There were many attempts to produce a form of solidified yeast which would be more stable, less bitter and easier to transport and store than liquid barm. It was eventually Austrian chemists who perfected the method of producing and compressing yeast using spirit distilleries. Dutch distillers then took the lead in the increased production of commercial yeast and in exporting it to the rest of Europe.
The Dutch yeast was not entirely without its problems and British bakers were wary of its properties, claiming that it was often bulked out with starch, chalk and even pipe clay and by 1900 there were a dozen - more reliable - yeast distilleries operating in the British Isles, producing 68 million pounds of yeast annually.
The Belfast Distillery produced 'Balloon' yeast, which carried the slogan Never Done Rising and was reputed to be of the highest quality. Another highly-recommended brand came from Hull. There was also 'Domo' yeast from East London, alongside 'Tiger' and 'Hepworths of Harwich' yeasts.
Today yeasts are produced and exported all over the world. They are reliable and of high strength, work fast and can be bought dried or compressed. It all started in an Egyptian culture over 5000 years ago...
Finally, here's a thought: one gram of yeast contains 20,000,000,000 (twenty billion) single-celled living micro-organisms.