Distinguish live-culture from pasteurized fermented foods

Only unpasteurized, live-culture products deliver the microorganisms — pasteurization kills them.

Why it works

Heat treatment (pasteurization) during processing kills the live microorganisms that are the active ingredient in fermented foods. Most commercially shelf-stable sauerkraut and pickles are pasteurized; most refrigerated versions are not. The live organisms and their metabolic byproducts — lactic acid, bacteriocins, short-chain fatty acids — are what interact with the gut ecosystem.

How to do it

1. Buy sauerkraut and kimchi from the refrigerator section with an ingredient list of just vegetables and salt.
2. For yogurt, confirm the label says "live active cultures" and lists specific bacterial strains.
3. Miso should be unpasteurized (most miso sold in refrigerated paste form is); avoid shelf-stable miso packets.
4. Kombucha should contain live cultures and not be heat-treated after fermentation.

Evidence

Whether live versus heat-killed organisms convey gut benefit is established in principle — live organisms colonize; dead ones do not. The distinction between live-culture and pasteurized products follows from this. (mechanistic)

Some research shows that heat-killed (postbiotic) bacteria still provide some benefits through immune signaling, but these effects are less well-characterized than live-culture benefits.

Common mistake

Buying shelf-stable sauerkraut or pickles (which are brined and pasteurized, not fermented) from the supermarket condiment aisle and assuming they provide the same benefit as refrigerated live-culture versions.