1/4 cup of mesophilic cultured dairy (see section below for different types of culture)
1 cup whole cream
Mix the culture and cream in a clean glass jar.
Screw on the lid and leave it at room temperature (around 20 C, 68 F) for 12-24 hours.
Once it has cultured, store in the fridge until use.
To keep an active culture, re-culture every 2 weeks.
You can find mesophilic dairy cultures in most grocery stores (eg. buttermilk). See the section below for more detailed information.
The first time you make sour cream it may take a little longer to achieve a sour flavour. It will depend on the quality of your culture. However, once you’ve established your culture, it should be relatively quick.
The cream will thicken as it cultures, but if you want a really thick sour cream, then strain it through a coffee filter (like Greek yogurt).