Linked from
The 41 pages that link to Lactic acid fermentation, each with the reason it gives.
YogurtNarrower topic: Yogurt cultures use this process to turn milk lactose into acid.
SauerkrautNarrower topic: This process acidifies cabbage and gives sauerkraut its defining sourness.
Sour creamNarrower topic: Bacteria acidify the cream, lowering its pH and contributing to its tang.
Crème fraîcheNarrower topic: Bacteria acidify the cream and develop its characteristic tang.