You often hear people say that "before Pasteur nobody knew about yeast," and that using yeast is a fairly modern invention. This is something even microbiologists believe. For example, the landmark family tree of yeast (Gallone et al 2016) paper came to the conclusion that the two big families of beer yeast (Beer 1 and Beer 2) both derive from a single ancestor around 1600 CE. But people have been using yeast deliberately much longer than that.

The earliest good descriptions of beer brewing are from the 16th and 17th centuries, and for the people who wrote these descriptions yeast is an obvious ingredient in beer. They have words for yeast, they know how to treat it, and there's no indication that this is a new thing, or that there's anything surprising about the use of this ingredient.

Danish cookbook, frontispiece

Let's look at one example, the first Danish cookbook. It was published in Danish in 1616, based on earlier German works. The first recipe is for bread, the second for beer, and that recipe doesn't say you should add yeast. It takes for granted that you already know that. What it does say is (my translation from the original Danish):

When you pitch the yeast, then take good care that you do not add it too hot or too cold, but when it is somewhat more than milkwarm.

And there is no question that yeast is meant, because the word used is "gierd", easily recognizable as today's Danish "gær". Literally it says "naar du setter gierd paa," which is interesting, because farmhouse brewers in both Denmark and Norway used "å sette gjær på" as the phrase for pitching yeast into the 20th century.

Note the context here carefully. In 1616 adding yeast to beer was such an obvious thing that the recipe doesn't even bother to say it. And not only that, but there already exists a word for yeast in Danish, and even a set phrase for pitching it into beer.

Medieval brewing, woodcut from Olaus Magnus's book

If we look at other sources from the same period we find exactly the same thing. Olaus Magnus, 1555, says to use "the dregs from the previous beer." Cristoph Kobrer, 1581, has a whole chapter on how to reuse yeast, both dried and wet. Andrew Boorde, 1542, says that apart from malts and water one should never add anything to beer, except "yest, barme, or goddesgood", three synonyms for yeast.

In other words, by the 16th century, all over Europe, adding yeast to beer was just as common as it is today. Whenever it was that human beings figured out that they could add yeast to beer, it must have been long before the 16th century. But when?

Sigmund with the yeast ring

Let's start with a little basic logic. Sigmund showed me how to use a yeast ring. You drag it through the yeast (either the foam or the slurry) so that it sticks to the ring, then hang it up to dry. When you want to use it, take a little wort and drop the ring into it. That's it. That's literally all you need to successfully reuse yeast. And from archive documents I see that people also used cloth, wooden branches, or even straw rings, seemingly with no problems at all.

Yeast ring in wort (at 10:09)

So people have had everything they needed to reuse yeast since the Stone Age. The only thing that was needed was to come up with the idea of taking the foam or the dregs from one beer, and putting it into the next. All you need to do is to think "what if I take some of the foam and put it in another beer? Will that make it foam?" It's a simple thing to try, and it obviously works.

Yeast ring in fermenting wort (at 14:35)

Not only that, but spontaneous fermentation starting from scratch is quite risky and can give all kinds of results. It can even be dangerous. So once someone came up with the idea of reusing the yeast from a successful brew it must have been blindingly obvious to everyone that this was a far better solution, and the method must have spread like wildfire.

Which still doesn't tell us when it happened.

In viking times, and also in prehistory, beer was brewed for specific celebrations. In fact, beer was so important for the main celebrations in life that to hold them without beer was unthinkable. In the guilds, for example, people would gather from a large area, brew beer, and have a feast a couple of days later.

Anders Christensen pointed out that if they were using spontaneous fermentation this would be pretty risky, because there would be no guarantee that the brew would be drinkable. It could also take a long time to start fermenting, yet there were strict deadlines involved.

Old Norwegian farmhouse, Lillehammer museum

Similarly, on the farms brewing consumed valuable grain. If many of the brews turned out bad that would be a highly costly proposition. In the 19th century Norwegian farmers usually brewed 2-3 times a year because they didn't have enough grain to brew more often. Yet in the viking era, and also before, every farm brewed. It's clear that somehow they were able to consistently produce good beer, and to do it quickly.

So, logically one would expect that the reuse of yeast began long, long before the 16th century. But can we prove it? Yes, actually, we can.

One early "recipe" that's often referred to as being written by Zosimus of Panopolis was actually not written by him. He lived in the 3rd and 4th centuries CE, long before the printing of books. So his works survive in manuscripts that were copied by hand, and in one of these chains of copies a kind of beer recipe appears that wasn't present in the original manuscript. The insertion is from around 1000 CE.

Distillation equipment, drawing from a manuscript by Zosimus

The recipe says very clearly: "Grind the remainder and make [it] into loaves, adding yeast as that for bread." The text is in Greek, and the word used for yeast is ζύμη, "zyme". That still means yeast in modern Greek, and is the origin of the words "zymology" and "zymurgy". But this is an ancient text, so can we be sure that the word meant the same thing then? Here's Max Nelson, professor of Roman history, in his PhD on beer in classical civilization: "The usual Greek term for yeast was ζύμη and the Latin one was fermentum." So, yes, we can.

And we have older sources as well. Pliny the Elder writes in 77 CE of the Iberians (Spanish) and Gauls (French) that they take the foam from fermenting beer and use it in bread, so that they have lighter and better bread than other peoples. It's very difficult to believe that they did this without also having figured out the far more obvious idea that this works for making beer, too.

Max Nelson's PhD is basically a collection of all the quotes relating to beer from all historical Greek and Roman sources, organized by subject. If we look at yeast we find this:

In one account of a beer-maker from the first century A.D. preserved on a papyrus from Tebtunis mention is made of "pitchers of yeast" [...], which tends to show that a leavened liquid was added to ferment the beer. In Greco-Egyptian papyri of the first and second centuries A.D. there is also found the profession of "yeast-maker" or "zymonrgos". This cumulative evidence tends to show that at least by the first century A.D. there were individuals skilled in the breeding and cultivation of yeasts for both bread and beer.

Model of Egyptians brewing, Rosicrucian Egyptian Museum, San Jose, California. (E. Michael Smith, Wikimedia)

So, what the documentary record shows is exactly what simple logic told us we should expect to find.

And there's no indication here that the reuse of yeast began around the first century CE. Nelson quotes sources from Egypt, but Pliny was talking about Spain and France. So clearly by this time the use of yeast was established practice over a very large area. It's entirely possible that the reuse of yeast is nearly as old as beer brewing itself, but so far the evidence for that, or against, is missing.

Delwen Samuel looked at dried-up residues of fermenting beer, from Amarna in Egypt. They date from around 1080 to 1550 BCE. Studying the residue under an electron microscope, she found what was clearly dried-up yeast cells. That was very likely Saccharomyces cerevisiae. However, this doesn't prove that the yeast was added deliberately, because even spontaneously fermenting beer is mostly fermented by that yeast. So pinpointing when yeast reuse began is going to be very difficult.

Ruins of Deir el-Medina, Egypt. (Steve F-E-Cameron, Wikimedia)

Sources

Natural History, Pliny, 77 CE. Book XXIII, chapter XII.

Koge Bog, indeholdendis et hundrede fornødene Stycker, anonymous author, Copenhagen, 1616.

Beer in Greco-Roman Antiquity, Max Nelson, PhD thesis, University of British Columbia, 2001.

Gründliche und Nütze Beschreibung der Weinhawer und Bierbrewer-Practick und der ganzen Kellermeister-Kunst, Christoph Kobrer, 1581.

Historia de Gentibus Septentrionalibus, Olaus Magnus, 1555.

A compendyous regyment or a dyetary of healthe, Andrew Boorde, 1542.

Archaeology of Ancient Egyptian Beer, Delwen Samuel, Journal of the American Society of Brewing Chemists, 54(1), p3-12, 1996.

Acknowledgements

Many thanks to Susan Verberg for sending me a translation of Cristoph Kobrer. Also many thanks to Max Nelson for giving me more background on the Zosimus recipe.