The first very simple trick is to use a small amount of liquid that contains sugar. In the case of kimchi I use either a small amount of rice vinegar or sweet chili sauce in addition to chili powder and dried chilis. The reason I do this is simple--it kick starts the fermentation process by providing some easy to digest food for the souring bacteria. The end result isn't sweet at all, since it is converted to acid, alcohol, and CO2, but getting that wild fermentation started sooner is better (less chance of spoilage/mold/etc.).
The other thing I do is to use as little salt as I can get away with to help promote more sourness. Salt seems to delay the fermentation process and limit how sour the pickle can get. I don't want something so sour that it makes you grimace, but I like the sourness to be more assertive than the saltiness.
Lastly, I like fermenting in bags instead of glass/crocks. I'm only making pickles for me (the wife likes them occasionally, but not as often as I do), so breaking out the ten gallon pickle crock is overkill, and glass can just be kind of a pain. So fermenting them in a ziplock bag is easy, convenient, and just the right size.
So, the approximate recipe for this kimchi is as follows.
- 2 medium heads of bok choy
- 2 large carrots julienned
- 1 tablespoon rice vinegar
- 2 teaspoons fish sauce
- 2 teaspoons Sriracha sauce
- Enough salt to make the vegetables lightly salty, about a teaspoon
- Dried chili powder to taste, about a teaspoon or two
- Small red dried chilis for presentation
Mix together, taste and adjust to your preference. What you are looking for flavor-wise is moderately fiery, lightly salty, and a full umami flavor from the fish sauce. You should slightly taste the sugar from either the rice vinegar or sweet chili sauce, but it shouldn't be dominant or 'sweet'.
Load the veggies into you favorite fermentor (glass jar, crock, baggie) and set it in a location that doesn't have any direct sun, but not some place you'll forget about it. Taste it every week, and when it reaches your desired level of sourness (for me pretty sour), load it into some glass jars and store in the fridge. It will last for a very long time--I have some kimchi that is probably eight months old packed into old spaghetti sauce jars, and while the color isn't great it is still very tastey.
One of my favorite ways of eating kimchi is actually in Asian noodle soups. If you are making a noodle soup and want to add a lot of wonderful flavor, crack an egg into it a few minutes before serving and soft boil it in the broth, and right before serving add a big clump of kimchi. Authentic? Not likely. Delicious? Absolutely. Half cooked egg yolk in broth with a fiery kimchi is one of my favorite things in the world.