The reporting on this has been utterly dreadful, and Seamus Blackley and his collaborators are jointly responsible for this. Just look at the headline:

A Conversation With the Team That Made Bread With Ancient Egyptian Yeast: How a scientist harvested 4,500-year-old yeast and turned it into a loaf of sourdough

Wow, they did it, right? They absolutely, definitively made sourdough from 4,500-year-old yeast! Oh wait:

"And, look, there may not be any ancient yeast in this. This could all be crazy, because we haven’t done all the science, and we’re going to. But it definitely acted different. It was really exciting."

What a joke. Blackley isn't a 13 year old at a science fair, and neither are his collaborators. They knew that publishing this as a tweetstorm with the disclaimers at the bottom would be open to misinterpretation, and it was. Here are a couple of lines from his tweets that would make anyone think they did it:

This crazy ancient dough fermented and rose beautifully. Here it is in the basket, just before being turned out to bake.

The crumb is light and airy, especially for a 100% ancient grain loaf. The aroma and flavor are incredible.

Yes, I blame all the journalists as well for not doing their fucking jobs and, you know, calling up actual scientists and Egyptologists who've already tried similar things.

The twitter thread is full of disclaimers like "Finally, I need to say again, this was just for practice". Yes, there's some uncertainty over whether they've actually got ancient yeast in sufficient uncontaminated quantities. Yes, it's a publicity stunt. No, we shouldn't actually care quite so much.

> calling up actual scientists and Egyptologists who've already tried similar things.

Like who?

I saw this in my Twitter feed a few days ago. Some hilarious comment included "Return of the yummy".

I've actually been experimenting with sourdough recently. It's very easy to get started with this and even the failures are pretty tasty. All you need is clean water, some decent flour and about 7-10 days to turn that into a stable sourdough starter. After that, you can just keep on growing it and baking bread, pizza, pancakes (oh yes), etc. Dangerously delicious. I could use less carbs in my life, though.

This is fascinating.

I do wonder whether sterilizing the flour had any effect on the output. Doing a control with the same flour and modern yeast seems potentially worthwhile.

It sounded like he already had experience with that. He said that flour always turns out like a “puck”, where this was fluffly. So, not exactly science-grade analysis there, but certainly a strong indicator.

The “puck” thing was about the type of grain he used. There was no indication that he’d previously sterilized said grain.

I really would love buying that yeast eventually to experiment with it, good business opportunity for them if the lab tests they are doing pans out.

I would buy.

Sell it as a kit with the right flour.

I happened on a fun radio interview with Seamus Blackley about this while driving this evening: https://www.cbc.ca/player/play/1583944259602.

Nobody got sick.

I’ve never heard of anyone getting sick from anything that looks and smells like sourdough and doesn’t have obvious mold. And people start their own starters all the time under extremely unsanitary conditions.

It turns out that the critters that infect people are usually pretty specialized and have a hard time living in dough.

yeah yeast hates salt.

humans are kinda salty.

Are you saying that the kind of yeast that ferments bread can’t tolerate salt? The salt I add to my dough on a regular basis disagrees.

As I understand it, there are two things going on. First, most (or even all?) pathogens can’t tolerate alcohol, and many baking yeasts produce alcohol. (Many sourdoughs produce very little, though.). A lot of pathogens also can’t tolerate the acids in sourdough either. Most importantly, baker’s yeast and sourdough cultures grow fast. The outcompete the nasties in dough. This is why a brand new starter can be funky, but this resolves itself after a few generations.

Bread yeast is different from other types of yeast, such as the kind you'd get a yeast infection from.

Same broad taxonomic Order but way different lineages in the same way that bears and corgis are in the same order. Similar enough -- fur, teeth, etc. -- but one is a useful friend, and the other will try to kill you, though serious threats are kinda rare.

If this was bread yeast, even old bread yeast, it'll probably be harmless, in the same way that the reincarnation of an ancient Egyptian cat will probably just act like any other cat.

Keep in mind that bread is baked until the internal temperature is usually 205F or so. It should be extremely safe, regardless of what yeast you used.

Some toxins produced by "bad" organisms can survive high temperatures of an oven, e.g. causing ergotism.