Do I need a starter culture for sauerkraut or kimchi?

Starter cultures for lacto-fermentation: when they help, when they don't

Vegetables come pre-inoculated with Lactobacillus plantarum, brevis, and mesenteroides on their leaves and skins. In most conditions, these are sufficient for fermentation to establish. Starter cultures (whey, previous batch brine, commercial LAB powders) speed the first 24-48 hours but are almost never required for safety or success.

Quick answers

Should I add whey or a starter to my first sauerkraut?

No, skip it. Cabbage's natural lactic bacteria are reliable at 2% salt and 68°F.

My batch didn't start bubbling in 3 days. Should I add a starter?

More likely you have a salt or temperature problem. Check the salt % (weigh, don't estimate) and make sure you're in the 65–75°F range. Adding a starter to an already-cold batch won't help.

Can I use brine from a previous batch?

Yes. About 1/4 cup of brine per quart of new ferment visibly speeds up the first 12 hours. Useful, but not required.

Does sourdough starter work?

No. Sourdough starter is a different balance of bacteria and yeast, tuned for bread. It isn't suited to vegetable ferments.

What about store-bought pickle juice?

Usually not. Most shop pickles are vinegar pickles and pasteurized, with no live culture. Only raw, refrigerated, naturally fermented pickles have live bacteria you can use as a starter.

Are commercial starter powders worth it?

If you're nervous about a first batch, they can help. After your first few batches, no: the bacteria already on the vegetables are reliable.