Sourdough Ecosystems – parallels between a sourdough starter, or rēwena/rēwana, and our environment

Over lockdown, many people discovered the joy of making their own bread using a sourdough starter – find out how this relates to protecting our local ecosystems.

By Hannah Davidson - Research Assistant, Science

16 July 2020

Read the author's biography

Lockdown loaves

Over lockdown, many people discovered the joy of making their own bread using a sourdough or rēwena bread starter. Having extra time at home, and perhaps frustration to vent by working dough, freed many of us to learn, or refine, our bread-making skills.

During morning zoom meetings, my EPA colleagues and I showed off our loaves hot from the oven. Working with a team of scientists who specialise in environmental DNA has bought a whole new dimension to our sourdough conversations. The fascinating science behind sourdough bread-making provides a neat analogy for how and why we need to look after our local ecosystems.

Read more about lockdown sourdough baking - stuff.co.nz website

Sourdough ecology

A sourdough starter is made up of different yeasts and bacteria in flour and water. When fed regularly with additional flour and water, the starter maintains a natural balance, and some of the starter may be removed to make bread.

These yeasts and bacteria (along with natural yeasts in the flour) help the bread to rise by eating sugars in the flour, and releasing bubbles of carbon dioxide. Rēwena uses potatoes to provide the sugars for the yeasts to eat.

Some starters, both sourdough and rēwena, have been maintained for generations, being passed down from baker to baker, whānau to whānau. They have their own whakapapa, and usually the precise mix of bacteria and yeast will be unique.

Ecosystems in our environment

This dynamic act of balancing a mix of different organisms is similar to how local ecosystems work. These also comprise a mix of many different species working together to maintain balance. That balance must also be maintained with different inputs into the environment, such as water and various organisms and chemicals. The biodiversity (or variety of living things in a certain place) of both sourdough and environmental ecosystems is critical for them to thrive.

Each local ecosystem is unique, with its own characteristics driven by many things – including what is alive and thriving, the climate and location, and what might be out of balance. For example, when a new species is introduced that becomes dominant in numbers it can kill or crowd out other species. A familiar example of this for us in Aotearoa is the predation of rats and possums on manu (birds), tipu (plants) and other taonga species in forest ecosystems.

Environmental DNA testing, which involves taking a sample of water from an environment and testing it to see what DNA is present (for example, from animals shedding skin cells), is a tool that can be used to learn about ecosystems. It can tell us what species are present in an ecosystem, and help us understand how healthy and in balance it is.

Keeping ecosystems healthy

Thinking about ecosystems holistically can inform how we go about keeping them healthy and thriving.

For a sourdough starter, you might discover it smells like vinegar rather than a sweet yeast, notice an absence of bubbles or see some mould to understand that it is out of sync. You would then know you need to take action to restore the balance of your starter.

For an ecosystem, you might notice the disappearance of species that indicate the environment is healthy; or that the water is a different colour; or that there is an increase in a species that may be harmful (like algae or rats). Using techniques such as environmental DNA, along with other environmental monitoring and mātauranga Māori, can help us understand our ecosystems and make decisions about the environment.

Video: Sourdough ecosystems | 1:16 mins | Transcript

Hannah Davidson's biography

Hannah hails from Otago/Southland, where she completed a Master of Science in Chemistry at the University of Otago, focussed on the topic of improving alternative plastic processes. Hannah joined the EPA in 2019 as Science Research assistant, bringing a passion for science communication and its role in environmental protection.