Raising Bread

Our recent piece on Voltaire on Vaccines led to a fascinating letter from Peter McLaughlin, full of breadmaking knowledge + etymological detective work, which he kindly gave us permission to share here.

In that blogpost, we cite Voltaire's explanation of smallpox inoculation as:

inserting [a pustule] removed from the body of another child ... like yeast in a piece of dough; it ferments and spreads its own qualities through the blood-stream.

Your humble author was confused about this as a description of bread-making; Peter explains....

Voltaire [1733] is writing before the isolation of yeast fungus by Pasteur [1857]. (There are early microscopic observations of what we now know to have been yeast cells before Pasteur, but he was the first to understand what he was looking at and what the role of yeast in fermentation was.) In the eighteenth century, pure dried yeast that bakers use nowadays didn't exist, and nobody knew what caused fermentation.

When people before the nineteenth century write about 'yeast', they're not referring to a fungus, but rather to the foamiest and frothiest part of the mixture left over from beer production. They knew that if you took some of this frothy liquid and put it into a bread dough (as Voltaire describes), it would ensure the dough would rise, which otherwise could be uncertain.

Nowadays we know that the frothy/foamy aspect of 'yeast' in the old sense is due to a high concentration of 'yeast' in the modern sense, and adding the foamy liquid to dough guarantees the presence of the right kind of fungus for the bread to rise, whereas if you didn't add it you were just hoping some atmospheric fungus had gotten into your mixture. But Voltaire didn't know that.

Voltaire was obviously French, and my knowledge here mostly relates to English and Irish (and to a lesser degree American) processes.

Using beer froth to make your bread rise was the standard in England / Ireland. But there was always an alternative method, to use a sourdough starter, which in French is called levain. This is basically what I was talking about in terms of just hoping that atmospheric fungus got into your mixture, except that French people had some culturally-evolved techniques which we now understand create evolutionary selection pressures that benefit the right kind of fungus.*

You would sometimes feed your sourdough starter with a bit off the day's batch of dough, or even use that bit of dough as the basis for a new starter, which is why historical texts sometimes talk about 'old dough' even though that's not quite right (if you just tried to use the old dough directly it usually wouldn't work - you need to turn it into a sourdough starter).

My understanding is that by the eighteenth century, more and more French people were using the English-style booze-based option, because it was more efficient at scale - indeed, modern commercial yeast is still produced by an industrial descendant of this process - but levain was seen as traditional.

The English version of Voltaire's letters unambiguously mentions yeast, which in eighteenth-century English meant only one thing: beer froth.** But the confusing thing is that the French version uses the word levain. I think the English version was published first, though I imagine Voltaire would have written the French first and then translated into English. [Ed: from our research, it seems so!]

I'm not sure what the eighteenth-century French word for this kind of beer froth was, or if there even was a specific word. But certainly by the nineteenth century the word used was levure. This was the word Pasteur used when describing his scientific observations involving beer froth, and in Dumas' Grand dictionnaire de cuisine (the standard late-nineteenth-century reference work for French cooking terminology) there is a clear distinction: levain = sourdough starter, levure = beer froth. And, just like the English word 'yeast', the French word levure changed meaning over time to refer to the fungus that Pasteur isolated.***

The weird thing is that, if Voltaire was thinking of sourdough starter, he could have used the noun 'leaven' in his English translation (slightly archaic-sounding today, but at the time it was a perfectly normal noun corresponding to French levain). But he used 'yeast', which in eighteenth-century English meant beer foam.

It's possible that in the eighteenth century levain and levure - which are obviously closely related words - had not yet been distinguished; in which case, the use of 'yeast' in the English translation suggests strongly that Voltaire was thinking of beer foam, as I suggested. This is my best guess (I think the metaphor makes most sense this way).

But it's not impossible that his metaphor was a sourdough starter; he just didn't know the right English word to refer to a sourdough starter, maybe used an unclear dictionary or asked somebody in England 'what is the word for the thing you add to dough to make it rise?', and wrote down 'yeast' even though it wasn't right.

* And also lactobacillus bacteria. And obviously it wasn't just French people, there were lots of people who had sourdough techniques, although it's important to realise that it was a cultural thing: implicit cultural knowledge passed down through poorly-understood rituals.

** see e.g. Dr Johnson's Dictionary:

*** Levure can also be used more expansively in modern French to describe anything you would use to make bread rise except for sourdough starter, including baking powder and baking soda (which weren't available in the eighteenth century, although predecessors like pearlash were - but that's a different story). There's also the phrase levain-levure, which refers to techniques like poolish and biga that use yeast (levure) to mimic some of the features of sourdough starter (levain).