When food decays, it teems with all sorts of bacteria, both good (probiotics) and bad.  When there's enough bad bacteria, it will cause illness if ingested.  Fermentation is a way of preserving food by altering the environment in which these bacteria live.  

Stage 1: Weeding Process

Certain conditions, including temperature, pH, nutrient and oxygen supply, cause different bacteria to thrive or die.  Fermentation happens in an environment where only probiotics can thrive and the key to that, in the case of kimchi, is salt. 

The most important part of making kimchi is salting the cabbage.   Probiotics can survive a salty environment; bad bacteria cannot.   It’s essentially a weeding process.  Mrs Kim, being an old school Korean mom, says it’s like the admissions process to Harvard.  Sort of, not really!

All you really need for fermentation is salt and cabbage.  In the olden days, kimchi was made with only these 2 ingredients and a bit of beef stock for flavor.  The extras – red pepper flakes, ginger, garlic, anchovy sauce, shrimp – are purely culinary, but provide additional nutrients. 

Stage 2: Party Time!

Without the presence of bad bacteria, our probiotic friends are now able to thrive.  The most common probiotic found in kimchi is called lactobacilli.  They feast on sugars in the cabbage and fruit, reproduce with abandon (cue the Barry White track), and release CO2 gas and lactic acid as a byproduct.  These byproducts are what give kimchi its unique taste and texture.  The CO2 gas causes kimchi to bubble, fizz, and occasionally, overflow like champagne when you open the jar (I told you it was a party!).  The lactic acid gives kimchi its wonderful tartness as well as further protection against harmful bacteria.  The production of lactic acid is very important because it lowers the pH to levels where other bad bacteria cannot be introduced, which contributes to the long shelf life kimchi is known to have.  This is the same reason why pickles last a long time as they are preserved in vinegar, which also has a low, acidic pH.

Stage 3: Slow Down!  

Temperature affects fermentation rates greatly.  In warmer temperatures, the motto for probiotics is “live fast, die young!”  Kimchi will ferment too quickly, meaning the probiotics will run amuck, exhaust their food supply, run out of steam and eventually die.  The end result is an overly sour, mushy kimchi that is best made into stew.  Into the cauldron, you go.  

“Everything in moderation” applies to probiotics too!  To keep things from getting out of hand, kimchi must be refrigerated after about 12-24 hours of fermenting at room temperature.  Probiotic activity slows down at lower temperatures, where they enjoy life at a more relaxed pace and for longer. 

Stage 4: Putting Probiotics to Use in our Bodies

Having a healthy population of probiotics in your digestive system keeps bad bacteria under control.  Bad bacteria produce toxic byproducts that make you ill, so you never want them to have the upper hand.  Too much bad bacteria in your gut is often a consequence of eating a lot of meat, processed foods, sugar, etc.  It leads to problems like constipation, bloating and inflammatory conditions.   Be sure to eat a majority of fresh veggies & fruit to avoid this situation from the start.  Also, incorporate other sources of probiotics in addition to kimchi, including yogurt, miso, cottage cheese and kombucha.  You want strength in diversity & numbers!