It was just 345 years ago that we discovered the existence of microscopic life, but in fact we have been using it for thousands of years. We get help from microbes for fermenting food, for instance, which helps preserve it for longer. Or we ferment drinks with various yeasts to make alcoholic beverages, such as beer. At Micropia we decided to make our own beer using our own wild Micropia yeast. But how do we catch a suitable yeast for making beer? Where do we need to look? In this blog we talk about yeasts, fermentation and beer.
Yeasts are single-celled fungi that naturally live all around us. The best-known yeast is Saccharomyces cerevisiae, more usually known as baker’s yeast or brewer’s yeast. This type of yeast is used in the production of bread and of most beers. Yeasts are facultatively anaerobic, which means they can grow both with and without oxygen. When a yeast burns sugars without oxygen in order to grow, it creates alcohol as a by-product. This continues until the sugar is used up or the yeast species can no longer survive the percentage of alcohol. So for our Micropia beer we wanted to catch a yeast that is resistant to alcohol, ensuring that the alcohol percentage can rise high enough for a tasty beer.
Going on the hunt
In October 2018 our hunt for yeasts took us all over ARTIS. We stood on the rocks of the Savannah, we gathered the fruits of a plane tree, we carefully took a little yeast from a beehive, we plucked tropical flowers in the Butterfly Pavilion and we harvested the last remnants from the edible garden. And all to find a good yeast that we can use to brew a beer. But catching specimens wasn’t the end of the story. How do you know that the stuff you have caught is a yeast, and not one of the countless other sorts of microbes you can find in ARTIS? And once you’ve found the yeast, you then need enough of it to brew beer. So all the catches now had to be cultivated in the lab. Cultivation allows us to test for various properties and thus to determine whether it is a yeast or not, and whether we have more than one type of yeast living in the cultivated sample. Some of this work involves using the microscope. By observing and assessing the cells we can find out whether we’re looking at single-celled yeast cells, and not something else such as a bacterium or a tardigrade.
Cleaning and upscaling
The catches with enough yeast in them now needed to be further cultivated and cleaned. Cleaning is done using a pure culture. This involves smearing the catch out over a growth medium and letting the microbes grow on this. Since the sample is spread out thinly, each microbe will grow separately from its neighbours in the culture. So after a while separate groups of cells arise on the growth medium, known as colonies. Each colony is derived from a single cell, and so each colony comprises just one species of microbe. The yeast is cleaned by removing the growing colonies from the plate and putting them in a liquid growth medium – this gives us a culture with only the yeast we want to use. In order to get the yeast used to the beery environment, the yeast was gradually transferred from our growth medium in the lab to wort, which is unfermented beer. Once the yeast culture had become sufficiently used to this new environment and was able to grow completely on wort, the culture was taken to the brewery. At the brewery the culture was diluted in more wort in a large fermentation vat, with the aim of brewing a large quantity of tasty beer. Then it was a question of sitting back and waiting for the final result. And this has turned out really fine: a delicious and unique beer with a special story.