Victoria Kirk - Producer

I always knew that yeast was an important part of beer making, but when Budweiser Brew Master Doug Muhleman took the National Geographic film crew to a steel reinforced door and said “this far and no further”, I knew there must be more to these microscopic organisms than I first thought.

Behind the locked door, preserved in liquid nitrogen was the very first strain of yeast used by Aldolphus Bush, the founder of Budweiser, over 120 years ago. Today it’s still used to give Budweiser its distinctive taste and of course its beer buzz. “Not only does yeast convert sugar to alcohol,” explained Doug “but it also creates a myriad of different flavors during fermentation. Yeast is responsible for a lot of the flavor in beer”. Considering the yeast behind the locked door in question, launched the Budweiser Empire, there was no chance we were going to get in. The risk of contamination was too high.

Intrigued, I decided to investigate further. The University of California Davis has one of the largest yeast collections in the world. It seemed like the perfect place to start. Biologist Kyria Boundy Mills, the curator of the collection took us into the main storage area. Here over 7000 different yeast strains and over 450 different spices were stacked in neat rows. “These strains represent over half of the world’s known species”, she said “we’ve isolated yeast from insect guts, decaying plant matter, cactus and in every imaginable habit around the world”.

So what is yeast? It turns out that yeast is a simple single cell organism with an incredible appetite for sugar. In just one-hour a yeast cell can eat its own weight in sugar. It’s what it does with that sugar that’s interesting. Kyria is working with biotechnology companies to produce ethanol from agricultural waste, potential medicines, pigments and different types of wines and beers. As an example she held up a test tube filled with what looked like grains of sand. “This yeast contains the same pigment that gives salmon it red color,” she said “we want to extract these properties and put them into fish feed for farm raised salmon so that they’ll be pink”.

It was a long way from beer, but I was beginning to understand why yeast was so important. Our next step was to watch yeast in action. Kyria took us to a yeast cryo-preservation chamber – a minus 80-degree deep freeze. Using gloves to protect her hands Kyria removed a single vial. Frozen yeast is dormant so her next step… yeast resurrection. It turns out it’s as simple as adding heat. Using a heat loop – a small metal pen that thaws the yeast cells, Kyria spread a few grains onto a Petri dish filled with a sugar rich solution. Under a microscope we watched the individual yeast cells come to life.

At first the cells looked round, then they began to change shape. “They’re budding”, she said, “ it means they’re growing, they’re alive.” If this was beer these yeast cells would continue eating and growing, dividing at exponential rates until all the sugar was converted into alcohol. It’s a process called fermentation. It is the job of the Brew Master to control the process, creating just the right amount of alcohol. At the Anheuser-Busch brewery in St’Louis, the fermentation tanks are temperature controlled. If the yeast starts creating too much alcohol, the Brew Masters simply drop the temperature, slowing down the yeasts ferocious appetite,

Kyria explained that yeast has another very important role to play in beer making – it determines if it’s ale or a larger. “If you use ale yeast its called top fermenting, it rises to the top of the tank and it usually ferments at a higher temperature,” she said. “This means it creates more alcohol and more flavor. So ales tend to be fruitier, more fully flavored.” She went on to explain, that laager yeasts are called bottom fermenting yeasts, they settle to the bottom of the tank and ferment at a relatively cool temperature. This is why larger is a lighter with less alcohol.

Ancient civilizations had no idea that yeast was responsible for intoxicating properties of beer – they put it down to magic or a gift from the gods. Modern science has unlocked yeasts microscopic magic – it’s but made it even more interesting. In the future we’ll be toasting new wines, new beers and even be curing illnesses. Kyria thinks there are still millions of undiscovered yeast species out there – so happy hunting Kyria.

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