Since the beginning of The Event (remain indoors!), people have been panic-buying flour. Lots of flour. More recently, some people on Twitter have also complained about how ordinary baking yeast is unavailable at the moment. For myself, that’s not an issue, as I have a healthy sourdough culture (named Penelope) that I now use more regularly to bake some delicious bread for both fun and sustenance. But others aren’t so lucky, so a question asked by many is whether brewers yeast is an acceptable substitute for baking yeast.

The short answer is: yes, they’re both Saccharomyces cerevisiae.

The slightly longer answer is: yes, just be aware that the pitching rates in baking are much higher than in brewing, so if you start using dry brewing yeast, your bakes will be very expensive. A good way to deal with this is to keep some of your yeast in the form of dough, like a sourdough, except not sour, and just regularly feed it with sugar or flour. That should make it possible to propagate the yeast for quite a while, making the last pack of bakers (or brewers) yeast last for quite a while longer.

The beer historian’s answer is: yes, they’re both Saccharomyces cerevisiae, and were a focal point of cooperation between the brewing and the baking trade. In the first half of the 19th century, it was common in Vienna for bakers to use top-cropped yeast from the local breweries. It was in fact their main source of yeast. Then something happened: in late 1840, Anton Dreher in Klein-Schwechat (just outside of Vienna) starting brewing using bottom-fermented yeast. His new types of beers became an instant hit in and around Vienna, and of course, other local breweries had to react and also introduced bottom fermentation to their breweries. This change went in fact so quick that within just five years, all the Viennese breweries had switched. The bakers weren’t happy, because that changed the yeast they could get from the brewers: while top-cropped yeast was previously plenty and of good quality, the new type of yeast was harvested from the bottom of the fermentation vessel, and was full of bitter hop compounds, hop resins and cold break (coagulated proteins), which tasted bitter and looked darker than previous yeast, making it unsuitable for baking.

The bakers first tried to import fresh yeast from outside Vienna, but this turned out to be infeasible as the yeast’s quality and health would deteriorate too quickly, so they needed to find another way to get a reliable yeast source, ideally making them independent from any brewers. So the Viennese bakers’ guild started a competition in 1845, announcing that they would award a prize to the person who could produce a leaven that was suitable for completely replacing the much sought-after top-fermenting brewers yeast.

The brewer Adolf Ignaz Mautner of St. Marx brewery went on and developed a system to industrially produce and press yeast. His general approach was fairly simple: first, a mash is produced and converted into sugar, then the mash is cooled and fermented. The resulting yeast can be harvested, washed and pressed.

For the mash, kilned barley malt and rye (in a ratio 1:2) are finely crushed and mashed in with hot water (3.5 l of water for every 1 kg of grist) to rest at 70°C for two hours. This should fully convert all starches into sugar, and also allow other contents of the malt to dissolve. This thin slurry is then chilled to about 28°C using a coolship, and then inoculated with a “mother yeast”, which is basically a smaller amount of the same type of mash that has previously been inoculated with pressed yeast or top-cropped brewers yeast and left to ferment until it is in its most active state. Essentially a yeast starter.

After about 10 to 12 hours, the fermentation is active enough to be covered with a thick foam, the yeast. This yeast is then skimmed and put onto a fine sieve that is slightly submerged in water. The idea here is to dissolve the yeast in the water, while other hard matter from the mash will be caught by the sieve. Using ice, the yeast can be made to fall out of suspension. This watered yeast is then mixed with high-dried wheat or potato starch flour, put into multi-layered linen bags, and then pressed. In terms of yield, 100 kg of crushed malt and rye produce about 8 to 10 kg of yeast, to which about 2 to 5 kg of starch flour are added.

This method is now known as “Vienna Process” and after a few improvements, it won Adolf Ignaz Mautner the Viennese bakers’ guild’s prize.

In later years, more improvements and new methods were introduced, such as a switch to green malt and corn (maize) for the mash, the introduction of single strain yeasts, as well as ways of promoting more yeast budding (and therefore a greater yield), such as aerating the mash or diluting it. These improvements increased the yield from 10% in the 1840’s up to 40% in the early 20th century. But essentially, pressed bakers yeast is still produced using methods that every brewer at the time understood, just used in a way to make yeast, not beer.

Adolf Ignaz Mautner was later made a knight of the Order of the Iron Crown, receiving the hereditary title “Ritter Mautner von Markhof”. While his brewing business was merged with the breweries of Klein-Schwechat and Simmering in the early 20th century to form a public limited company, the Mautner Markhof family remained in the food business. While family sold their business to German food company Develey, Mautner Markhof still exists as a brand in Austria, for products such as mustard (and other condiments), vinegar and pressed yeast.

And that’s how baking yeast has historically been the same as (top-fermenting) brewers yeast, and how its production was turned into an own industry by a brewer using beer brewing methods.