Mix the oats with the culture and 1 cup of water in a glass container.
Cover with a tea towel and leave to ferment in a warm location overnight or for up to 2 days.
To cook, boil 1 cup of water and mix into the oats. If it’s not warm enough you can cook the oats for a few minutes in the microwave or on the stove top.
Usually, I make fermented oatmeal with milk kefir. You could also use other dairy cultures like buttermilk and yogurt.
For vegan oatmeal, culture with vegan yogurt or kombucha.
The kitchen counter is fine for soaked oatmeal. However, if you want a strong sourdough flavour, then stash your fermenting oats somewhere warm, like above your refrigerator, near a heater, or beside your hot water tank.