Beer brewing, woodcut from Olaus Magnus's History of the Northern Peoples, 1555

It's often said that before Pasteur's work on yeast (and Emil Christian Hansen's introduction of the pure-yeast system) all beer was sour. Various lines of reasoning lie behind this claim. One is that all beer was spontaneously fermented back then, because nobody knew what yeast was. Another is that because brewers had no microbiological control over their yeast, they were effectively using wild yeast, and thus they would necessarily get sour beer. Many people claim there must necessarily be other organisms than pure brewer's yeast in these yeast cultures, and that these would turn the beer sour.

All this was a long time ago, however. Pasteur did his work in 1857, and Hansen developed his system in 1883. What do we know today about the result of brewing with uncontrolled yeast, the way people did before the pure yeast system? Actually, quite a bit.

Historical sources

Beer brewing, also from Olaus Magnus

Let's start with historical sources. In 1555 the (nominal) archbishop of Sweden, Olaus Magnus, published an account of the northern peoples. In book 13 there are several chapters dedicated to wine, mead, and beer. He describes both sweet and sour wines, but of beer he says that people brew it sweet or bitter according to preference. He says winter water is the best, as it never makes the beer go sour. Today we can see what was really going on, but he was right that beer was less likely to go sour in winter, due to lower temperatures. He says winter water is used in the brewing of Danzig beer, "the noblest and healthiest beer". It's clear from the text that to Olaus Magnus, beer is a sweet or bitter drink, and mainly sour by accident.

In 1616 what is known as the first Danish cookbook was published. It's really a Danish translation of a book first published in Bavaria in 1598, by one Anna Wecker. The second recipe is for beer. She writes of the recipe that the beer is "thick and well-tasting, but in summer it doesn't keep long, because it soon sours." Her proposed remedy for that is to let it boil well, for 2-3 hours, and to use lots of hops.

In 1780 the first account of sahti brewing was published by Carl Niclas Hellenius. He says that using unmalted rye flour is not good, because being unmalted it "does not give in the same degree as the barley the suitable sweetness to the drink." Later he writes that one of the trickiest things in brewing is adding the yeast at the right temperature. If the yeast is added when the wort is too cold, the beer sours.

The title page of Hellenius's article on sahti brewing

I have several more pre-Pasteur sources on beer brewing, all of whom say the same thing. Beer should be sweet or bitter, but not sour. However, preventing it from going sour can be tricky, especially in summer, and it doesn't always keep very long. It's not that beer cannot keep, however. Olaus Magnus writes of beer kept for 10-20 years, and Ticcander in 1792 writes of Finnish beer that was best when kept 2-3 years. And so on.

As for knowing about yeast, all of the sources describe adding yeast as a key part of the process. Olaus Magnus (1555) says one adds the dregs from the previous beer, or if these are not available, bread yeast. A few chapters earlier he talks about using yeast when making mead. Anna Wecker (1616) simply says to add yeast. Hellenius (1780) likewise. So obviously people knew about yeast and what role it plays in brewing, and using it was already well-established practice.

Own experience

Brewing with kveik

All this is just me interpreting old texts, however, and as such not conclusive. However, I have another source of information, which is my own experience with beers fermented with exactly the sort of uncontrolled yeast that was used before Pasteur and Hansen. Let's go through those:

So I feel reasonably confident in saying that beer does not need to be sour just because one doesn't use a pure yeast strain. From the historical sources we know that's how people usually brewed, even before Pasteur.

But what about the purity of the cultures?

Microbiological analysis

Dried kveik from Stranda, Norway

So far two kveik cultures have been analyzed by professionals. In both cases the cultures were found to be pure Saccharomyces cerevisiae. One such culture from Lithuania was DNA-sequenced and found to be odd, but still Saccharomyces, if not necessarily Saccharomyces cerevisiae.

So that seems pretty definite, but intriguingly, we still have one more line of evidence to explore.

Chemical analysis

The title page of the book containing the analysis results

There is not a whole lot of 19th century beer available for chemical analysis, but it so happens that Ron Pattinson has dug up a whole raft of chemical analyses of 19th century beer that include analysis of the acid contents of the beers. According to Ron below 0.1% is good, above 0.2% you get a detectable tartness. Another source says lactic acid makes up about 0.18%-0.52% in geuze, which seems to fit well with what Ron wrote.

Going through Ron's results we find:

Curiously enough, these analyses are pretty unanimous in that the beer had more lactic acid than you'd wish. Nearly all of the averages are below Ron's 0.2% threshold, and the ones from Kiel are well below even the 0.1% level, but it does mean a good number of individual beers were above 0.2%.

So what does that mean? My guess is that sanitation and refrigeration during transportation and in bars may have left something to be desired. Even so, the beers were not sour, but a good number had an acidic tartness to them.

On balance, I think it's fair to conclude that most pre-Pasteur beer was not sour, but that a good bit of it was tart. And that very likely the use of non-pure yeast was not the cause of the tartness.