Yeast tastes good. And no, I'm not talking about all the wonderful foods that yeast ferment
for us, like bread and beer. I mean the yeasties themselves. They taste good. Boil a packet
of dry yeast in a little bit of water to kill the yeast, maybe put in a little pinch of
salt, and taste the resulting broth. You know what that tastes like? It tastes like mushroom
stock, which I suppose should not have surprised me as much as it did, considering that mushrooms
and yeast are the same basic thing.
They're both edible funguses, and so they taste a lot alike. They both taste meaty.
As we have discussed in previous videos, the fungal kingdom is arguably a lot closer to
the animal kingdom than it is to the plant kingdom. And fungi have a lot of the same
kinds of things in their bodies as we animals do, such as the amino acids that taste umami-y.
We need to eat protein to live, and protein sources that are good for us are likely to
contain glutamic acids and some related organic compounds. And therefore we are evolved to
find those compounds very, very tasty. That's umami. That's the savory, meaty sensation
we get on our tongue. And yeast have a lot of it.
Again, maybe you already knew this, but I was completely floored by the taste of a boiled
packet of bread yeast. That is good soup. And now I understand why so many processed
foods have yeast extract on the ingredients. Check out the ingredients on nearly any dried
soup product — Cup Noodles, or this one, this Lipton noodle soup. Look on the back
and you will see yeast listed on the ingredients. Or more specifically, a yeast extract that
has been juiced out of the yeast. That's it right there — yeast extract that I juiced
out myself. I'll show you how I did that in just a minute. Boil that yeast juice down
and mix it with some reduced vegetable broth, and you'd basically have Marmite, this gooey
brown stuff the Brits like to spread on toast. The Aussies have a similar condiment they
love called Vegemite.
And if you taste this stuff, it tastes a lot like that reduced yeast extract, because that
is in there. It also tastes like celery and some of the other vegetables that they put
in here — basically concentrated vegetable stock is in here as well. There's also a third
distinct and very strong taste in here, and that is the taste of beer. Indeed, the story
of yeast extract begins with beer. When you brew beer, there is a ton of leftover yeast
— way more yeast than you would ever need to brew your next batch. And probably even
more than the bakery down the street would need to rise their bread. Historically, spent
brewer's yeast was regarded as a waste product.
Then came Marmite, a company founded in 1902 in the English beer-brewing Mecca of Burton-on-Trent.
According to the company's own history of themselves, the founders based their concept
on research done by the German food scientist Justus von Liebig. Liebig is also the guy
whose work led to the dubious chef wisdom that searing meat seals in the juices, which
it doesn't. In his own lifetime, Liebig was much more famous for inventing a liquid meat
extract that he said could replace a solid food diet, which it couldn't. But it did taste
really good. And Liebig's product eventually became the English stock cube maker, OXO.
Liebig also did work on yeast and sometime in the 19th century, he is purported to have
done basically what I did here in my kitchen.
I took a whole jar of active dry bread yeast from the grocery store and I dumped that into
water. Liebig used some spent yeast from a brewer, which probably would've come to him
already suspended in some amount of water. In his experiments, Liebig heated this solution
to a balmy temperature that activated enzymes within the yeast cells. I don't know what
exact temperature he used, but in 2007 these Turkish researchers determined that the optimal
temperature for making yeast extract is 50ºC, 122ºF. So that's what I used. Unfortunately
for me though, 50ºC is kind of just below the minimum temperature that you can reliably
hold in a domestic oven or on a gas stovetop. You're probably going to get a temperature
a little higher than that. And at that point, you risk denaturing the enzymes in the yeast
that we need for this process. So — electric heating pad.
It took me a while to find the right setting and the right way to wrap this around the
bowl to get my target temperature. And even when I did, the temperature suddenly shot
up when my dried yeast woke up and they started metabolizing the energy stores in their little
unicellular bodies. That is their body heat, thermogenesis. I had to rip the heating pad
off so that my solution did not overheat, but then the yeast calmed down after a while,
because I didn't give them any food to eat in that water. So they just kind of stopped
metabolizing, my temperature plummeted. So I had to put the heating pad back on. And
when I did that, I was not able to get the temperature up high enough. This just wasn't
hot enough. I was only able to hold my bowl at like 35ºC for a day. And basically nothing
happened. This is not yeast extract. It's just warm yeast in warm water. It tastes okay,
but not super strong.
And you generally don't want to eat very, very much live yeast. Speaking of microorganisms
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But anyway, yeah, I could not get enough heat to squeeze the juice out of my yeast. So I
went out and I bought a much bigger heating pad. I tied it snug around the bowl with a
cute little scarf and there, a perfect 50ºC. I held it there for 24 hours, which the aforementioned
Turkish researchers found as the optimal time to achieve what Justus von Liebig achieved
before me, and that is yeast autolysis. It's funny — we just talked about autolysis last
week when we were talking about gluten proteins in flour. Autolysis basically means cellular
self-destruction. At this temperature in water, enzymes within the yeast cells break down
their own cell walls, causing their little yeasty guts to spill out into the solution
and further reactions break down their proteins into more of the tasty umami-y amino acids
and such that we like to eat.
That semi-clear liquid is the lysate — the extracted cellular guts dissolved in water.
I should have just siphoned it off the top because my filter here did not do such a great
job of removing the solids that had settled on the bottom. Those solids are what's left
of the yeast cell walls. That's what's in the slurry there: cell wall debris. It's often
filtered out with a centrifuge at yeast extract factories. I suppose it dilutes the flavor
of the extract, but I will say it actually makes kind of a nice thickener. Here's some
homemade yeast extract that I did not filter at all. I boiled it down. I put in some onion
powder and some celery seeds to mimic the vegetable flavors they add to Marmite. And
that's honestly some good vegan gravy right there. The cell wall debris gives it a really
creamy texture.
I will say that creamy texture could be due in part to an additive that they put in grocery
store bread yeast like this. It's called sorbitan monostearate. It's an emulsifier. They put
it in there to keep the yeast from getting too dry when they're in storage. And also
it helps the yeast to rehydrate inside the dough. Seems possible to me that this additive
is forming a water-and-oil emulsion here in this solution with the lipids naturally present
in the yeast. And that might be contributing to that creamy texture. And it also might
be making my extract harder to filter. I basically have yeasty mayonnaise gumming up the works.
But for what it's worth, I also did a test with an organic yeast packet that does not
have any emulsifier inside it. And when I boiled that down to a paste, it still had
a somewhat creamy texture. So, who knows?
All I know is, according to the story, Justus von Liebig filtered the solids out of his
lysate, he boiled it down to a glaze and he was struck by how closely the taste of that
resembled a reduced animal stock. That's basically vegan demi-glacé. Quite tasty. So based on
Liebig's experiments, these folks built a factory in Burton-on-Trent, and they tried
to work out a process for converting cheap, ubiquitous spent brewers yeast into a food
fit for human consumption. One problem they ran into is that brewers yeast is covered
in bitter residues from the hops. You have to de-bitter the yeast. And even after they
do, Marmite is still a little bitter. I'm told most people who eat this on toast do
a very thin layer, and then they cut it with some butter. I do think that's quite tasty,
but it does still very much taste like beer.
Whereas the extract that I made from bread yeast does not. Nor does this so-called nutritional
yeast taste like beer. Not at all. This company says they grow their own yeast in a molasses
solution rather than getting it from brewers, so there's no hops residue, there's no grain
residues. But it's not a yeast extract. It's whole yeast, baked until they die and they
form little flakes that you can use as a seasoning. It's quite tasty, but not nearly as strong
as the extract — because of all of the cell wall debris that's still in there, I assume.
I had hoped to be able to give you a practical recipe for homemade yeast extract. There are
a lot of ones on the internet and they all have big problems in my opinion, and I did
not do any better. One problem is that this bottle of yeast is $6 and you want to see
how much extract I was able to get out of it? This much. That's what I got. Not very
cost-effective. I also do worry about the sorbitan monostearate content in here, the
emulsifier. Every food safety agency on earth considers that stuff perfectly safe in the
amounts that you would eat if you were using a little dry yeast to bake a whole loaf of
bread. I have no idea how much of it you would end up eating in a concentrated yeast extract.
And I have no idea if that amount would be safe. No idea.
I figured I could remedy both of these problems by simply growing my own yeast at home from
one little starter packet. I put one little packet into about a gallon of sugar water,
and I watched it bubble for a few days before I realized that I'm basically making rum here.
This is now a terrible-tasting alcoholic beverage that you could distill into rum. The thing
about making alcoholic beverages, it's actually kind of tricky to do well. You could get all
kinds of contaminants in here. This had a pretty funky smell. And the bread yeast seemed
to shut down long before they'd fermented all of the expensive sugar I gave them. There's
not that many yeasties in there, and I was totally unable to filter them out of my stanky
bathtub hooch. Maybe you can figure out a good way to grow yeast at home for extract.
Or maybe you could get it from a friend who home-brews. The problem is then you would
have to de-bitter it. And apparently, the processes that they use for de-bittering yeast
at the factory are pretty industrial, pretty intense, not easy to replicate at home.
So maybe just buy yeast extract instead. Here in the States, I get Marmite at the grocery
store, Publix, which has a British import section, #NotAnAd. This is the same import
section that has these OXO cubes that are nearly solid yeast extract. There's no animal
product at all in these. People originally considered yeast extract to be an adulterant
in stock cubes — a cheap imitation of real meat. But I think this stuff is great in its
own right and I'm not even a vegan. If you are a vegan, definitely check out yeast extract.
It's rich in the B vitamins that can be tough to get if you don't eat any animal products.
Indeed, researchers like this American chemist in 1916 came to understand the necessity of
B vitamins in part through their experiments with yeast. They fed pigeons a diet of only
plain white rice and the birds got really weak and wobbly. Same thing happens to humans.
We call the resulting disease beriberi. The researchers gave those pigeons white rice
fortified with yeast extract and the pigeons got better, because B vitamins. Yeast — one
of humanity's best friends.