Use 6 ounces/180 milliliters (6.1  fl oz) if you are certain of the freshness of the starter. When in doubt, use a full cup of buttermilk as starter.;
,, Shake thoroughly to mix. Label the jar with the date.
 This should take about 24 hours. If you find it takes longer than 36 hours, the starter was no longer active (meaning that the bacteria has died). The buttermilk may or may not be tasty if it takes longer than 36 hours but it can still be used for baking.
 This happens because the bacteria have fermented the milk, and the lactic acid is causing the milk proteins to thicken. Refrigerate immediately.
Add a bacterial starter of 6 to 8 ounces/180-235ml of active fresh cultured buttermilk to a clean quart jar.
Fill the rest of the jar with fresh milk.

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Screw the lid on on securely.
Let the jar sit out in a warm part of the room until thickened.
Check to make sure the thickened buttermilk coats the glass.
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