The original purpose of the tea bag was to be able to easily remove the tea from the hot water after a specific brewing period, when tea will tase its best. Then there is the added benefit of convenience - a removable device means that tea can be made as easily in a mug as in a pot, without the need for a tea strainer, and that tea pots can be kept clean more easily.
Before tea bags were eventually developed, Popular infusers included tea eggs and tea balls - perforated metal containers which were filled with loose leaves and immersed in boiling water, and then removed using an attached chain. Tea bags were first introduced in the United States in the early 19th century, developed by Thomas Sullivan, a New York tea merchant, in 1908. The British however, were naturally wary of such a radical change in their tea-making methods, therefore did not adopt it until the 1950’s. The convenience factor was more important to the British tea-drinker than the desire to control the length of infusion time, hence the appearance of tea bags that did not have strings attached.
When tea bags were first developed and marketed, the idea was simply to package a few whole tea leaves in paper packets. But this method proved to be slow and complicated; it wasn't long before tea was processed in grinders and reduced to fine dust. This efficient technique increased the production of teabags but at the cost of quality.
Tea that is broken and pulverized becomes a stronger tea as it is brewed in the cup. These finely chopped teas release a lot of heavy tannins to the disadvantage of the delicate tea aroma and flavor.
Overtime, marketers have altered tea bag contents in response to a perceived notion of consumer expectations. These consumers, it was said, expected color in their cups; you could see it in the way they frantically jiggled the tea bag, as if the depth of color correlated with good flavor. The tea industry therefore began to fill their tea bags with ever more finely chopped leaves that's release their deeply colored tannins almost immediately.
If you want to taste good quality tea, loose leaf teas with no bags are always the best option.
When brewing tea, maximize the surface area and give the leaves enough space to move. The leaves will unfurl after contacting water and release their various components. The water takes on the color and fragrance of the leaves and assumes a distinctive texture and a variety of flavors.
The longer the leaves are in water the more thoroughly the components are dissolved. Maximize the surface area and give the leaves enough space. If you allow the complete unfurling of the leaves of a traditional black tea (a Darjeeling or a Yunnan, for example) during the brewing process, they can occupy four times their original volume. Japanese green teas can expand seven times, and oolong pearl teas (such as Dong Ding, Gao San Cha, or Tie Guan Yin expand 18 times!