I bought Nordic Saison from Hill Farmstead and loved it. I have a Saison recipe that I really like and I want to try and sour that. I took the dregs from a 750ml of the Nordic and threw it in a small starter (1.030). I'm including a photo after three days. It looks like things are going well but I need to create another starter to bolster the culture. Maybe a step up to 1.040 and maybe 1.5 liters this time. Can someone confirm this and include any tips?
Also I read some references (after the fact) to using an airlock with sour starters. What's the reason for this and did I ruin it by not doing that?