These are low oxidation teas (around 5%) that are meant to capture the freshest flavors. Due to green tea trying to capture the fresh flavors, they are also quite strong. This is why we brew them at a lower temperature, to slow the extraction of those strong flavors.

Although many places grow tea, there are 2 major cultures when it comes to the production of green tea: Chinese and Japanese. Japanese monks brought tea over from trips to China as early as the 8th century during the Nara period, although it would take several centuries for tea to catch on for more than religious monks or other higher classes. Eventually, Japan began to grow its own tea culture focused on the health benefits believed to be gained from it. They would adapt their own methods of processing tea until the 1700s, where they would start to adopt the methods still in use today. 

• Chinese method: Leaves are picked early in the morning and left to wither during the day, around 12 hours. Come night time the leaves get heated up in large woks which get up to over 530 degrees Fahrenheit, for only around 10 minutes or so, just to halt the oxidation process from being able to take place. Because the kill green process happens so quickly in the processing of the green tea, it allows for the leaves to keep most of their form and more fresh flavors. At this point most leaves will go through a rolling process, some being more gentle than others. This rolling helps to spread the flavorful oils around the leaves, as well as change the presentation. From this point they are places in dryers which can get quite hot for a short time until the water content is low enough for storage and sale. 
• Japanese method: Like the Chinese method, the Japanese start their process of withering after the morning pickings, although the time it is left for can vary and even be much lower than the time that Chinese producers leave theirs for (around 4-12 hours). Once an acceptable amount of the water content is extracted through the withering, the Japanese then put the leaves in a large turning drum where there get steamed for a couple of minutes. This is done in a precise moderation, as too much steam will make spoil the leaves while too little will encourage oxidation. Once they are taken out of the steam drums they are placed into wooden drums where they will be turned for around a half an hour in warm air to remove most of the rest of their humidity. From this, they are then rolled for only around 10 minutes to let the oils coat the leaves. After this short rolling process, they are sent to dry again for another 30 minutes or so. Some processors will put the leaves through a polishing step at this point, which results in the leaves getting the iconic flat and shiny texture sometimes associated with Japanese greens, although this is not always done. At this point, they are just left to dry in warm air until the water content is low enough for storage.