If using the starter culture, stir together the culture and water. Let the mixture sit while you prepare the ingredients—around 10 minutes. If using kefir whey, add it when the recipe calls for culture.
Place the tomatoes, onion, cucumbers, salt, and pepper in a large bowl and toss to combine.
Add the mixture to a one-quart glass jar that can be securely sealed.
Add the Cutting Edge Culture or kefir whey and cover with water, leaving an inch or two at the top.
Seal the container and let it sit on your kitchen counter, out of direct sunlight, for 2 days. After 2 days, place the container in the refrigerator.
When ready to serve, scoop tomatoes and cucumber mixture into a bowl. Toss with parsley and drizzle with olive oil. Serve immediately.
Storage note: This can be kept in a covered airtight jar in the refrigerator for up to three weeks.