Gyokuro is the highest quality shelf shaded sencha that has been hidden from the sun for 21 days. This causes both the theanine and the caffeine in the tea leaves to increase, which yields a sweet Umami flavour. This type of cultivation is also used in producing tencha, (碾茶)
Gyokuro production in japan is under 1% from the total tea produced during the year, it requires special attention and specialist care trough each process.
My personal suggestion to enjoy this unique tea is to brew it with cooler water 50°C