Why water temperature matters? The relationship between bitterness and fertilization

Theanine is one of the amino acids to give umami taste. It can be manually increased by nitrogen (N) fertilization, but overfertilization of nitrogen also results in bitterness and astringency as it also increases other N-based compounds such as caffeine and catechins. Of course, this is not the case for this Nagomiyutaka kamairicha.