Temperature control is key with fermentation. When it comes to kimchi, I think the ideal temps are probably ~55-60°f at the beginning of the ferment and then going down to the 40s once the pH comes down a bit. Some people recommend fermenting completely in the fridge; their hearts are in the right place but normal fridge temps are too cold and hold back a good ferment. Kimchi made that way never really develops and tastes slightly bitter.
Fermenting at room temperature usually produces kimchi that gets too sharp before it gets to develop. And it’ll take its toll on the texture as well.
The main reason kimchi fermentation vessels are buried underground is temperature control.
If you don’t want to buy a kimchi fridge and don’t have a really cool spot to ferment in, here’s a nontraditional method I suggest (I even suggest it if you do, for reasons that will become apparent):
Ferment kimchi paste by itself ahead of time. I make a paste with garlic, ginger juice, gochugaru, onion, shiitake powder, and kelp powder (and 2% salt (don't include weight of pepper flakes and powders when calculating the salt weight)). If you have a vitamix or food processor, you can blend all the veggies together and then fold in the powders. You can also add the fish sauce and ingredients like that at this point. Don't be afraid to get weird with it. For vegetarians, I recommend liquid aminos.
So then you gotta set up the paste to ferment at room temp. Once the pH comes down below 4.6, you can throw it in the fridge and it will keep for a long time.
On kimchi day, brine your veggies (wet brining is the way to go, but I have nothing against dry brining and do that too), and then once they’re good and brined, take them and mix them with this pre-fermented past, some sugar, and, optionally, some sweet rice flour porridge (btw, I’ve heard that using soybean flour in the porridge is a good way to prevent the kimchi from getting too sour in time, but I’ve yet to try it) and set it up to ferment. But because you have the pre-ferment with a strong culture, this kimchi will get pretty active pretty quickly. Usually, I only let the kimchi stay at room temp for one day, maybe two, before throwing it in the fridge to cure for 2 weeks before using. Open the jar up and give it a gentle stir a few times during the ferment to let some funky air out.
This method is great for fresh kimchi too: the combination of the developed fermented flavors of the paste and the fresh crunchy veg…. **chef’s kiss**
But this method is great cause you have kimchi paste on hand to use whenever you want and can just kimchi anything easily at that point. Plus the veggies don’t have to sit and lose their texture at room temperature waiting for all the flavors to come together. You can also use this paste as a little flavor bomb in sauces and marinades too.
Also, use Asian chives and Korean Radish. I know they’re not easy to find, but if you’re lucky enough to live near an H-Mart or some place that carries them, use them in your kimchis. They’re great ingredients for salads and stir fries and a whole lot more too.
Here's a rough approx modified at-home version of the fishtown ferments kimchi recipe:
2 medium onions
~25 cloves garlic (~1/2 cup minced)
2T ginger juice (or minced ginger)
1/4 cup fish sauce or soy sauce or similar
1/4 cup water
1 Tablespoon sea salt
2+1/4 cups gouchgaru
teaspoon shiitake powder + teaspoon kelp powder (opt., not as called for if you're using fish sauce)
Tablespoon calcium chloride (opt.)
Blend water, salt, CaCl, and veggies together, blend it to smithereens, then fold in gochugaru and powders. Ferment at room temp for at least one week. Then keep in fridge.
1-2 heads napa (about 6 lbs or so), de-core then cut napa in half longways, then cut the halves crosswise into 1 to 2" wide pieces
Sprinkle with about 1/3 cup salt and a heavy pinch or two of calcium chloride (the calcium chloride will dissolve in the cabbage water that is released) and let it dry brine for a couple hours at least. Move it around so that you're getting all the cabbage sitting in its own brine as it comes out. You can brine overnight in the fridge if you want to.
When ready to assemble, get together 2 cups of matchsticks of Korean radish, ~3/4 cups of cut up scallions, ~3/4 cup of cut up asian chives.
Rinse the napa cabbage under cold water and ring that excess water out.
Mix brined cabbage, cut up veggies, a big pinch of sugar, and as much pre-fermented paste as looks good to you together in a bowl. So then set everything up to ferment in a sealed container with an airlock (preferably) and let it go at room temp for one day. After that, keep it in the ferment set up, but keep it in the fridge to cure.
There you go.