Trying to answer as best I can: Your culture won't smell like alcohol and it won't smell like bread yeast. It will have it's own unique sourdough smell.
Yeast gives off alcohol as part of the process. Different yeasts have different tolerances for how much alcohol they can stand. Basically once the alcohol gets to a certain concentration, the yeast will go dormant. Similar mechanics with beer.
The fact that your cultures doubled is good news. But remember, once the yeast exhausts the available sugars in the flour, they will stop bubbling. That's normal.
If you are leaving your cultures out at room temp, you'll exhaust those sugars quickly.
When I refresh my culture, I leave it out on the counter until it's bubbling and has almost overflowed the container. At that point it goes into the fridge. I will leave it there up to a month before doing another refresh.
Hard to explain but your culture should have a sourdough smell. I can't think of anything to compare it to. Using supermarket sourdough for this may be an exercise in futility as those breads can be pretty lame. My guess is there's nothing wrong with yours.
The only thing I can think that's different from what I do is leaving it out at room temp for more than half a day.
You can abuse sourdough starter up to a point but once you say you're sorry it's your friend again.
Time to make some bread?!
When I was young and poor I baked all the bread my family of 5 ate, for several years. I baked yeast and sour dough breads with various flours.
So some hints: 1. Use good bread flour! King Arthur's or Hecker's brand, if those are not available look for a high gluten wheat flour, if possible unbleached.
2. Get good at making yeast breads first. Yeast is more efficient than lactoacid bacillus and will make bread rise better. Once you have made a few batches of nice home style white, then try adding in some different flours. I used to make oatmeal, rye and Anadamer bread. All of which are variations on white. None of them will rise as well due to the lack of gluten. Then add your sour dough to the yeast dough. Yes, you can get sourdough to rise without yeast but it will take much longer and occasionally fail. Adding the sour dough starter to a yeast dough will still get you the great sour flavor with the bonus of a better success rate.
3 There is no substitute for kneading. You generally can't stir enough flour into a dough to make a firm bread, you have to knead in the last couple cups. Your problem really sounds like not enough flour being kneaded in at the end. Your boule should be smooth and have a dusting of flour on the outside. You can over knead, if the dough starts to tear rather than stretch just let it rest for half an hour.
Best Answer
It is not dangerous, but it is not necessary.
Sourdough starter is not going to ruin it, but it is not going to be REAL kimchi. Kimchi is really easy to make plus it tastes better when naturally fermented. Some people even prefer to ferment it in the fridge. It is going to take longer, but it's going to taste differently.
The is nothing unnatural about the SS, but SS is not natural for fermentation of kimchi. It is not used traditionally. It also might alter the kind of yeast and bacteria that are present in kimchi. The microorganisms present in naturally fermented kimchi are: Bacillus mycoides, B. pseudomycoides, B. subtilis, Lactobacillus brevis, Lb. curvatus, Lb. parabrevis, Lb. pentosus, Lb. plantarum, Lb. sakei, Lb. spicheri, Lactococcus carnosum, Lc. gelidum, Lc. lactis, Leuconostoc carnosum, Ln. citreum, Ln. gasicomitatum, Ln. gelidum, Ln. holzapfelii, Ln. inhae, Ln. kimchii, Lactobacillus kimchii, Ln. lactis, Ln. mesenteroides, Serratia marcescens., Weissella cibaria, W. confusa, W. kandleri, W. koreensis, and W. soli. The bacteria and yeast present in SS are somewhat different.
If you are going to add some sourdough starter, it will still come out well, but it's not going to be authentic. My question is: do you want to make REAL kimchi (김치) or do you want to make your own version of kimchi?
As an avid supporter of Korean cuisine, I want to take it one step further: James Oliver's recipe doesn't sound very Korean (sorry). He omits Asian pears and adds daikon which is predominantly used in radish kimchi (깍두기).
From my personal experience, kimchi tastes best when it is naturally fermented, no starter needed.
I also recommend an authentic Korean recipe which is surprisingly easy to make, here it is:
https://www.youtube.com/watch?v=fznTL6TzsqI
The only thing that I personally do differently, I don't add sugar at all, just more Asian pears. It still comes out nice.