Traditional methods and new technologies alike provide unique ways for tea fans to determine the correct temperature when boiling water for tea. From the shape and size of bubbles to electric tea kettles with built-in precision gauges, we will explore the nuances of measuring water temperature. This includes a cooling your water down technique for green tea, thermometers, electric tea kettles, hot water dispensers and the traditional Chinese method of examining water bubble size. Let’s get ready to boil!
Modern Methods:
Cooling Your Water Down: For many simply 
bringing water to a boil is the easiest and most practical way to brew water for black, oolong or pu-erh teas. Opinions on whether to bring your water to a full or rolling boil (212 °F) do vary. Many recommend a lower temperature of around 205°F because at 212 °F water becomes stale and deoxygenated. The more oxygen water has, the more taste and smoothness you will find. If you think about, it’s recommended that when you taste wine, you swish the liquid around in your mouth like mouthwash. This adds oxygen to the wine and helps bring out its full flavor. Professional tea tasters slurp their tea to do the same.
Regardless of your approach to the boiling issue, the question then is what to do about getting the water temperature right for green teas. One method is to bring water to a boil and then wait 2 minutes or so for the water to cool to around 180°-190°F. This certainly isn’t perfect since the time it takes for water to cool to this temperature can vary depending upon how much water is used to begin with, the room’s temperature and the brewing device size. 
Thermometers: A cooking thermometer provides a useful and precise way to measure your water temperature. As the water boils, you insert the thermometer into the tea kettle and take it off the stove when the correct temperature is reached. If you don’t have a tea kettle, note that a pot from the kitchen works just fine for boiling water.
Electric Tea Kettles: A variety of eletric tea kettles are produced that allow you to choose the relevant temperature setting for your desired tea. One fine example made of stainless steel is the Breville Variable Temperature kettle. It provides you with 5 pre-set brewing temperatures for Green, White Tea, Oolong, Black and French Press for coffee. Cuisinart offers a tea kettle, the PerfecTemp Tea Kettle that that sits right on the stove and has a built-in thermometer. Other companies like Bodum and C,apresso make electric water kettles without temperature settings. While convenient for boiling water at your desk for example, they are lacking the precision of the preset water temperatures.
Hot Water Dispensers with Temperature Settings: Hot water dispensers are available that allow you program in preset water temperatures for a variety of teas. Zoojirushi of Japan makes many different types of these dispensers including the Zojirushi Hybrid Water Boiler and Warmer in Stainless Steel. These dispensers are handy in that you can keep larger quantity of water hot for periods of time at your desired temperature. There is nothing like having hot water on demand for tea. We use Zojirushi machines at Mighty Leaf when we cup teas for tastings.
Traditional Chinese Method: The Chinese traditionally distinguish five stages of how water can come to boil for tea. James Norwood Pratt in his ‘The New Tea Lover’s Treasury” says: “The Chinese distinguish five stages of tea water as the boiling point is approached: “shrimp eyes,” the first tiny bubbles that start to appear on the surface of the kettle water, “crab eyes,” the secondary, larger bubbles, then “fish eyes,” followed by “rope of pearls,” and finally “raging torrent.” If you have a glass tea kettle you can watch the bubbles through the glass and if a standard kettle, take a peek by opening the lid. The kind of bubbles correspond with the following types of teas and their appropriate brewing temperature:
Shrimp Eyes: Tiny bubbles the size of a pin head that resemble shrimp eyes begin to rise to the surface and pop. A slow and gentle vapor of steam will show. At 155°-174°F this temperature is ideal for delicate green teas.
Crab Eyes: Water that gets hotter will then produce larger growing bubbles about the size of crab eyes. Vertical streams of steam rise up during this stage. At around 175°F this temperature is perfect for brewing white, delicate green and greener oolong teas.
Fish Eyes: Bubbles resembling fish eyes (about the size of an average pearl) rise to the top of the kettle as the water heats up. More steam is present moving in thick columns than in the Crab Eyes stage and the kettle will make louder noises. At 175°-180°F this temperature is ideal for green tea or white teas. However, remember that if your green tea tastes bitter, the water is too hot.
Rope of Pearls: At 195°-205°F, a steady stream of large pearl size bubbles stream to the water’s surface. This temperature is ideal for black, some oolong and pu-erh teas.
Raging Torrent: Water that sounds like a raging torrent with swirling and rolling bubbles is called ‘ruined water’. At 212°F this is considered to be de-oxgyenated and flat or what is traditionally called ‘old man water’. Please note though that 212°F or a full boil is recommended for herbal tisanes to bring out the herb’s full flavor. Exceptions to do exist though.
Remember, regardless of what method you choose, the key is that you enjoy the process and the flavor of your tea. Let us know what your preferred method is or what your daily boiling ritual looks like? Happy boiling!