Takuan (pickled daikon)
Japanese pickled daikon radish, usually bright yellow, crunchy, sweet and salty with a pungent aroma.
Takuan is daikon radish that is traditionally air-dried and then pickled for weeks or months in rice bran with salt; mass-produced versions are often made more quickly in a sweetened brine and dyed yellow. It is firm and loudly crunchy, tastes sweet, salty and slightly sour, and has a distinct, somewhat sulphurous smell that is noticeable when the pack is opened. It is eaten in thin slices as a side to rice, cut into strips for sushi rolls, or chopped into rice dishes, where its bite and freshness matter most. It is available at Asian grocers, usually vacuum-packed as a whole piece or in slices in the chilled section, and by mail order; once opened it keeps for several weeks in the fridge if tightly sealed.
Substitute:
Korean danmuji, the yellow radish used in kimbap, is practically the same thing, just usually sweeter and milder, and is often found in Korean shops. At a pinch, thin strips of daikon can be pickled overnight in sugar, rice vinegar, salt and a pinch of turmeric: the crunch, colour and sweetness come close, but the matured, pungent depth of the rice bran is missing.