No you don't need a culture. BUT, you can speed up a lactobacillus ferment with some whey so you can use less salt.
You need fresh whey and you can make your own easily. Just get a quart of a plain unflavored yogurt. Be sure it's 1 with "active cultures". Take a strainer and line it with paper toweling. Place over a bowl or jar. Put the yogurt in the strainer and let drip into the bowl. What's in the bowl is whey and what's left in the strainer is "Greek " yogurt.
Depending on how big of a batch you are making, you only need a couple of tablespoons of the whey to inoculate the batch.
Carol
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