This one worked quite reliably for me with about 180g of flour. https://www.hefe-und-mehr.de/en/2015/05/brotbacken-fr-anfnger-xi-sauerteig-ansetzen/?noredirect=

This one worked quite reliably for me with about 180g of flour. https://www.hefe-und-mehr.de/en/2015/05/brotbacken-fr-anfnger-xi-sauerteig-ansetzen/?noredirect=en_GB https://www.hefe-und-mehr.de/en/2015/05/brotbacken-fr-anfnge... You can always ask around in your friendly neighborhood forum for a starter culture, there's a lot of people that are willing to share. If you have bakers yeast, you can just feed it and multiply the amount trivially: Half a cube (20g) or 7g dry yeast, mix with 15g sugar, 100g flour, 100g water, let rise for an hour or two in a warm place. Fill in icecube form, freeze. Each cube is about half as strong as a "regular" cube, so you may need to experiment a little with rising time for your dough.