Yeast, our best friend, ancestor and savior

Much before we domesticated wild wolves into friendly dogs, we started the process of domesticating wild yeasts into yeasts we could use for our benefit. And funnily enough, humans and yeasts share a common ancestor, like how humans and chimpanzees share the same ancestor!

Humans and yeasts have shared a remarkable partnership for thousands of years and one variety of yeast stands out: Baker’s Yeast. Renowned for leavening dough to create fluffy bread, its contribution to humanity goes far beyond baking.

Let’s explore what yeasts are, their fascinating relationship with humans, and their significant contributions to humanity, including the solutions they offer to help safeguard our planet.

^{Yeast helps us stay healthy.}

Yeasts, the granddaddy of humans

If you remember from your science classes, all living organisms are made up of cells. In the present world, there are organisms which are made of just one cell, called the unicellular organisms like bacteria and yeasts, and then there are the multicellular organisms such as animals, humans and plants and trees and the filamentous fungi (with a thread-like or filament-like structure).

However, the Earth was not always this paradise of diverse species of plants and animals. A billion years ago the planet was home to only unicellular living organisms, which divided into two groups over time, based on differences on cell level. Some of these fungi evolved into yeasts after a few hundred million years. But evolution never stops! So, some of these decided to come together and evolve into multicellular organisms. They kept evolving and evolving, and over another few hundred million years they evolved into apes. And from the apes evolved human beings.

So, now you see, how we humans are related to yeasts!

So, how similar are the yeast genes to human genes? At least 23 percent of the genes in yeast are similar to those in humans despite this 390-million-year gap!

An interesting study looking into these similarities gained global attention. A group of researchers from the University of Texas at Austin took the most commonly used yeast called the “Baker’s Yeast”. Its scientific name is Saccharomyces cerevisiae.

The researchers identified 414 genes in the Baker’s Yeast which are essential for the yeast’s survival and replaced them with similar genes found in human beings. They found that the yeast variety could survive even with human genes in 47 percent of the cases!
 

The domestication of yeast by humans

Now that you understand the ancient and deep relationship that yeasts and humans share, it’s time to understand when and why humans domesticated yeast. And what exactly do we mean by “domestication” of yeast?

Picture this: Our ancestorsare walking through the forest searching for food. It would be nice to hunt an animal and eat its meat. But it’s not so easy! So, they are also searching for fruits.

As our tired ancestors drag their tired feet, they come across something exciting – a fruit tree with a lot of ripe fruits fallen on the forest floor around it. These fruits have not gone bad but are just riper. They pick it up, smell it, and take a bite. There’s a slightly funky taste to it, but that’s okay, combining elements of sweetness, fermentation, acidity, and complexity. So, they collect all the fruit, save it, and eat it later. Little did they know that the fruits they picked up had some kind of yeast growing on them, which was fermenting the fruit, giving it a funky taste that is both intriguing and richly textured. And it’s due to alcohol!

Alcohol, but how?

^{Yeast is everywhere.}

Well, here’s a fact about yeasts – they are everywhere. Yeasts are on our skin, on trees, on the forest floor, and on fruits as well. Like us humans, yeasts need food to gain energy and survive. They get this energy by consuming carbohydrates, similar to how we eat food.

So, what happens when we eat carbohydrates?

Well, we derive energy from the food we eat and expel all the unwanted stuff as stools. Similarly, when a yeast eats carbohydrates, it derives energy from it – but the waste that it expels after eating is alcohol and carbon dioxide gas!

This process by which yeast converts the carbohydrates it consumes into energy for itself to survive and expels alcohol and carbon dioxide as waste is known as fermentation. It is the same process that takes place when bacteria are added to milk to make yogurt and in the dough when you mix it with yeast and leave it for a few hours. During this time, the yeast consumes carbohydrates in the dough and expels alcohol and carbon dioxide gas which makes the dough airy. When you bake the leavened dough, all the water, alcohol, and gas are released by the heat, and you get the yummy bread.

So, when a fruit falls from the tree and gets damaged, the yeast living on its skin start consuming the sugars (carbohydrates) in the fruit. The yeasts start eating the sugars and expelling alcohol, which is what gives the funky flavour to over-ripened fruits. This is what happens in winemaking – grapes are collected from vineyards, they are crushed, the yeasts on them start fermenting the sugars in the grape juice, and after some time, you get grape juice that has a lot of alcohol in it, which is the wine.

One study has claimed that humans evolved the ability to digest alcohol because of eating fermented fruits around 10 million years ago. Otherwise, alcohol might have been even more toxic to us than what it is now.

So, as our ancestors got used to eating fruits with funky flavours, they slowly started realising that foods do not get spoilt immediately if they are fermented. Over the next many millennia, humans started learning that fermenting food is one way of preserving it.

^{Early fermentation.}

Anthropologists have provided indirect evidence that fermentation existed even when humans hadn’t fully evolved into their modern form. They point out that early humans started using fermentation to preserve food. This was even before pottery was invented to store the food. There exist even now methods of fermenting food that do not require any containers, for instance “open air fermentation”, allowing wild yeasts and bacteria from the environment to inoculate the food. One recent proof of fermented food without any containers is a 9,000-year-old site in Sweden where bones of hundreds of thousands of fermented fish were found by archaeologists in a pit.

As humans unlocked the secret of fermentation, over hundreds of thousands of years, they continued collecting wild yeast-covered food and fermenting it. They unknowingly domesticated wild yeast into a more domesticated version of fermenting yeast, the same way wolves got domesticated into dogs.
 

Yeast and enzymes

So, now you know that yeast performs fermentation – it consumes carbohydrates and produces alcohol and carbon dioxide gas. But how does the yeast do this? We humans also eat carbohydrates, but don’t expel alcohol from our bodies! We have to buy it from the liquor store. So much for us and yeast sharing the same ancestor from a billion years ago!

This difference between us and the yeast is that when it encounters carbohydrates, it immediately springs into action and releases a cocktail of natural substances called enzymes that kickstarts the fermentation process. While our human bodies also produce various kinds of enzymes, we do not produce the ones that can convert carbohydrates into alcohol.

But all this knowledge about yeast is recent and researchers are still unravelling the secrets of yeast and exploring their various applications in human lives.

The word "enzyme" itself is a testament to the significant role of yeast in fermentation, as it is derived from the Greek words "en" (meaning "in") and "zyme" (meaning "yeast"). So, quite literally, enzymes are the "yeast within" – the invisible players driving the magic of fermentation.

One of the key figures in advancing our understanding of yeast and fermentation was Christian Emil Hansen, a Danish microbiologist working for Carlsberg in the late 19th century – not to be mistaken for the contemporary founder of Chr. Hansen, now Novonesis, Christian Ditlev Ammentorp Hansen.

^{Emil Christian Hansen.}

Christian Emil Hansen’s groundbreaking research focused on isolating pure yeast cultures, which was a pivotal moment in brewing science. His meticulous work not only improved the consistency and quality of beer but also provided valuable insights into the fermentation process. He laid the foundation for modern brewing practices and opened new avenues for the application of yeast in various industries, emphasizing its critical role in both fermentation and enzymatic activity.
 

Baker’s Yeast, a.k.a Saccharomyces cerevisiae

As research intensified into yeasts, it was realized that one yeast is dominant wherever humans used yeasts for their benefit - Saccharomyces cerevisiae, popularly known as Baker’s Yeast.

As scientists studied yeasts, they started looking into Baker’s Yeast to thoroughly understand its genetics, biology, evolution, and potential applications for humans.

The years of research on this tiny organism by researchers across the world revealed a wealth of information paving the way for countless discoveries and innovations.

Unleashing yeast’s potential to address global challenges

As scientists explored every facet of its biology, a pivotal breakthrough innovation was achieved in the 1980s: the production of insulin using Baker’s Yeast.

How was this achieved?

Well, let's paint a picture: imagine yeast as a versatile chef in a bustling kitchen. Typically, this chef excels at crafting delicious bread, fermenting dough, and baking it to perfection. But what if we tasked this chef with creating something entirely different – say, a special sauce?

In our analogy, insulin represents that special sauce – a vital hormone essential for regulating sugar levels in the body. However, our culinary expert – the Baker’s Yeast – doesn't naturally whip up insulin; it's not part of their usual repertoire.

So, scientists devised a clever solution: they taught the yeast how to make insulin. Picture it as handing the chef a brand-new recipe card, complete with ingredients and instructions for concocting the special sauce. By modifying the yeast's genetic code, scientists effectively equipped it with the recipe for insulin production.

Once armed with this new recipe, the yeast gets to work in its kitchen. Instead of its usual routine of transforming carbohydrates into alcohol and carbon dioxide, it shifts its focus to crafting insulin. To accomplish this feat, the yeast becomes a veritable artisan, fashioning its own tools – enzymes. These enzymes act as specialized kitchen utensils, aiding the yeast in efficiently converting carbohydrates into insulin. It's akin to the chef not only cooking the sauce but also handcrafting the perfect tools needed to craft it flawlessly.

After a period of diligent work, the yeast successfully cooks up a batch of insulin. Scientists then collect this insulin, purify it, and make it available to individuals who require it to manage their blood sugar levels.

^{Yeast made into miniature insulin factories.}

In simple terms, yeast can be transformed into miniature insulin factories!

This breakthrough represents just one of the many applications of yeast that humans have innovated upon, stemming from early research into their remarkable capabilities. Since then, the number of applications has expanded exponentially. However, even though there are more than 1,500 known varieties of yeast, Baker’s Yeast continues to be the most popular in all applications.

Let’s take a look at some solutions offered by yeast

As mentioned, yeast is also helping humans deal with some of the most pressing challenges when it comes to environment and sustainability:

1. Biofuel production:
Remember, that yeast can consume carbohydrates to gain energy and expel alcohol as a byproduct, which we call fermentation? Well, some researchers used this ability of yeast to ferment carbohydrates such as corn and sugarcane to produce a type of alcohol called ethanol. Ethanol is a fuel which can be used in vehicles, from cars to aeroplanes. By utilizing yeast in bioethanol production, we can reduce our reliance on fossil fuels and lower greenhouse gas emissions.

2. Carbon capture and utilization:
As humans pump billions of tonnes of carbon dioxide into the atmosphere each year causing global warming, there is an urgent need to reduce levels of the gas in the atmosphere. Scientists have developed yeast-based solutions for capturing carbon dioxide from the atmosphere and even converting it into something of high use to humans like biofuels, biochemicals, or proteins.

3. Green chemistry:
Yeast is increasingly being utilized to replace harmful chemicals in industrial processes – which is known as green chemistry. Harvesting the fermentation power of yeasts and their ability to produce enzymes, yeast can be used to produce biological chemicals that are replacing synthetically produced chemicals used in various industries.