Sourdough is ancient and super hot at the same time. It can be used for all types of bread, but it is essential to the rye bread. It is the sourdough that gives the rye bread its characteristic taste and what makes it rise. You can bake rye bread using baking yeast, but it is not really the same. Despair not sourdough is easy enough – you just have get it started and to get in to the routine of keeping it alive. Here you can read about sourdough and how to bake with it.
The microbiology
It is not necessary to understand everything that goes on in the sourdough, but it is nice to have some basic knowledge. A sourdough is alive. Roughly speaking, a sourdough consists of three elements; lactobacilli, yeasts, and what they eat. The lactobacilli are responsible for making the dough sour or acidic. It is the same type of bacteria used in yoghurt cultures. They create an environment with low pH hostile to many other types of bacteria. In that way they are somewhat conserving the sourdough. And it should be mentioned that they are beneficial to our digestive system. The yeast are single celled fungi. They can withstand the low pH of the sourdough. Both the yeast and the lactobacilli can live without oxygen, but can also use oxygen for their respiration if present. If there is no oxygen the lactobacilli produces lactic acid, while the yeast produces alcohol. This is fermentation, as known from brewing or from the German sauerkraut. When oxygen is present, they produces carbondioxide like we do as we respire. When bread rise it is the carbondioxide from the yeast that makes bubbles inside the dough. In the field of microbiology there is a ground rule saying that it is the microbe or microbes which are best fitted to an environment that takes over the environment. So keeping a sourdough alive is a question of creating an environment to which the lactobacilli and yeast are best suited. They can both live from the starch in the flour, they need water, and they can live both with and without oxygen. Flour and water is the substrate in which we grow lactobacilli and yeast. When the sourdough is put away in a closed jar in the fridge it gets more sour, because the lactobacilli don’t get oxygen and hence produces lactic acid. If the yeast thrives in the closed jar it might produce alkohol and the sourdough smells a little like beer.
Getting a sourdough started
The internet is filled recipes for sourdough. A quick search on YouTube will give you a lot of tricks and tips. But make it easy, remember that a sourdough consists of three elements. Flour and water are both easy to get by. Just make a mixture in the ratio 1:1. Luckily enough, lactobacilli and yeast are also easy to get by. The air is filled with them. So just leave the mixture on the kitchen table and give it a stir from time to time. After a couple of days it starts to bubble, and you got a living sourdough. You can also get the lactobacilli and yeast from other sources. You can simply add a little baking yeast and some yoghurt. In that way you are improving your chances of success and you might speed up the process. Organic fruit peels are also covered in the wild yeast and lactobacilli from the air. Adding apple peels or grapes can also accelerate the process. Lastly, honey contains wild yeasts, which comes along with the pollen collected by the hardworking bees.
Using a sourdough
Everytime I want to bake rye bread, I take my sourdough from the fridge and pour it into a bowl the night before. Then I add a little water and flour (approximately a deciliter of each) and stir it before I go to bed. In the morning the sourdough has raised and is filled with bubbles. Before I mix in the rest of the ingredients I test whether it can float. I simply drop a teaspoon in a glass of water. If it floats the sourdough is active and perfect for baking. If it sinks i blend in a little water and flour and test again in half an hour, then it usually floats. Normally, 2-3 deciliters of sourdough suffices for a portion of rye bread dough. And now comes the most important note: remember to save a deciliter in the fridge for your next rye bread.