It is very easy to make a perfect cup of green tea. All you need is good tea, good quality water heated to the right temperature, and the correct steeping time. These directions are usually written on the bags of tea that you receive.
To get the maximum flavor from your tea it is best to avoid using tap water. Filtered water is good, but the best for tea making is spring water that is neither too hard nor too soft. Mineral content varies by brand and source so it is best to experiment with different spring waters and discover the one that makes the best brew.
A high water temperature between 180 degrees F to boiling will produce a cup of tea that is highly aromatic and slightly bitter.
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In ancient times in China tea lovers would travel great distances to get the right water for each variety of tea. Lower water temperature 140F to 160F will produce tea that has a mild aroma and a sweeter taste.
The way you brew it is up to you. It might be a pot, traditional Chinese gaiwan, tea mesh ball, disposable or reusable tea bags or an infuser.
1) put the tea in the infuser
2) pour water
3) wait the suggested time
4) take the infuser out
5) enjoy
Most of the green teas can be re-infused, but the tea leaves should be warm when re infused.
so if your tea leaves became cold it is better to discard them. In Chinese medicine cold tea leaves are considered as poison.