Monday Aperitivo – Sourdough: Living Cultures

Written by Julia Sick, edited by Michael Bom Frøst, photos by Yi-Ting Sun.

And we did it again! The Nordic Food Lab hosted its 4th Monday Aperitivo at the University of Copenhagen on the 19th of March. Our guest speakers included Rasmus Kristensen from Jalm&B, Associate Professor Emerita Åse Hansen from the Department of Food Science at University of Copenhagen and bartender Hardeep Rehal owning the cocktail bar Blume in Copenhagen.

The ingredients for this time’s lecture were flour and water…and some microorganisms, which are most often overseen too easily despite their importance to bring that gluey mass of dough to life.

Human’s use of the living culture can be tracked back 5000 years. Back then, people did not have an explanation for the spontaneous rise of bread, and rather explained it by either magic or religion. With the development of scientific microbiology in the 19th century, the rise of bread was attributed to the presence of wild yeasts from the atmosphere. They form a symbiotic relationship with lactic acid bacteria that create the characteristic sourness in the dough that is not present in most bread made with baker’s yeast.

The science table

All guests started with a tour around the “science table”. You cannot see the tiny microbes with the naked eye; however, you can see and smell the consequences of their microbial activity.

A set-up of various samples demonstrated influences of different grain varieties, fermentation time and temperature. A little “pre-taste”, if you can say so…

Set-up of the science table with different sourdough starter cultures and grain varieties.

Microscopic image of wild yeast and lactic acid bacteria from a cultivated rye sourdough. The LAB:yeast ratio in sourdoughs is generally 100:1.

The debate of the flavor creator

While the smell of freshly baked bread already crossed our smell receptors, we moved straight to our research kitchen to listen to the interactive talks between Åse and Rasmus.

But before that Rasmus, who clearly masters his craftsmanship, prepared some tasters of freshly baked sourdough bread and asked for a short sensory evaluation. We concluded on a mouth-watering bread with complex flavor and a balanced acidity, good crust and a moist crumb that was “gelatinized” with evenly distributed alveoli (wholes in the bread).

Åse, the omniscient researcher with over 50 years of experience in sourdough enriched our knowledge about its microbiology and fermentation properties. As she informed us, the sourdough flavors are developed during a long fermentation process that requires at least 12-24 hours, while fermentation through baker’s yeast only takes 1-2 hours. The lactic acid bacteria are mainly responsible for the acidification of the sourdough, whereas the yeasts are very important for the production of flavor compounds and some acids.

Rasmus mentioned that the bread that we purchase nowadays in supermarkets are most often made with commercial yeast, undergo a very short fermentation and contain various additives for preservation and taste. Therefore, he supports the idea to provide supermarkets with sourdough bread to make it available for all of us, however, this brings its challenges. One of the main difficulties is to maintain a stable culture of wild microorganisms to control the fermentation process and to achieve the same results each time. Sourdough needs to be more controlled as the variation in the composition of specific microorganisms depends on the fermentation conditions, such as flour type, extraction rate, water content, fermentation temperature, fermentation time, and how the sourdough is refreshed, as Åse explained.

Rasmus shared his experience that when serving his own bread to his friends and colleagues, they observed easier digestibility and overall better well-being. Åse explained this by the fact that grains cannot be fully digested by human, but a long fermentation allows the present microorganisms to “predigest” the indigestible compounds for us. Additionally, the nutritional value is enhanced by the use of whole grain flour as it contains a higher content of free minerals, which are made available for us during the long time of fermentation as phytate, a phytic acids, prevents the absorption of these minerals.

What’s sourdough doing in a cocktail?

For our aperitifs, we had the honor to host Hardeep. For a second, you might wonder what cocktails have to do with sourdough? And well, after this afternoon we can tell you: a lot. The first drink created was based on a sourdough extraction, basically, a rye sourdough fermented for 48h, centrifuged and pasteurized. The extraction added a mix of fruity, tangy and lemon-like flavors that he combined with Aquavit, unripe rhubarb juice and fresh dill.

Grains are the fundament for making sourdough, so the second drink was based on an extraction of 2h slowly roasted and milled purple wheat. The liquid was siphoned with nitrous oxide directly into a glass, which resulted in an exceedingly creamy and delicate texture with savory notes of cacao, coffee and cardamom.

Hardeep Rehal introducing the cocktails

Thanks to all contributors that joined us this afternoon!

Read more about our guest speakers here:

Åse Hansen, Associate Professor Emerita, Department of Food Science, University of Copenhagen.
Rasmus Kristensen Instagram from Jalm&B Instagram
Hardeep Rehal Instagram, from Blume Instagram


Åse Solvej Hansen (2012), Sourdough Bread, In Hui, Y.H. & Özgül Evanuz, E. Eds. Handbook of Plant-Based Fermented Food and Beverage Technology, Second Edition, pp.493-516