Screw on the lid and leave it somewhere warm for 4-12 hours.
Store in the fridge.
Try to re-culture within 2 weeks to keep the culture active.
The first time you make your buttermilk, it may take a little longer to achieve a nice flavour. It will depend on the quality of your buttermilk culture. However, once you’ve established your culture, it should be relatively quick.
Use buttermilk for fermented baking, making cottage cheese, or as a nice alternative to milk.