Peel and core the pineapple. Dice into ¼-inch pieces and add to a medium-size bowl.
Mince the cilantro, green onions, and jalapeño; add to the pineapple.
Mix in sea salt, whey or water kefir, and water.
Transfer to a quart-size fermentation vessel. The brine should come at least 1 inch above the level of the pineapple mixture. If it doesn’t, weigh the pieces of fruit and vegetables down with glass weights or another clean object. Seal the jar with an airtight lid or a lid with an airlock system. If using canning jar lids, be sure to “burp” the jars as needed during fermentation.
Ferment 2 to 4 days at room temperature, or until bubbly and fermented to your taste, before transferring to cold storage.