We often discuss in the shop with customers the things that happen when you steep non-Fukamushi Sencha (Senchas that start as needles and unfurl fully during the steeping process).
There are 3 things you need to pay attention to: the tea-to-water ratio, the temperature of the water, and the steeping time. If you use more tea or higher temperatures, you may want to lessen steeping time.
Tea-to-water ratio for Senchas are about 1 gram to 30 mls of water as a rough estimate, but may need to be adapted for different teas. Pic 1: 7 grams of Saekaeri Sencha in a 200 ml teapot. Pic 2: 45 second steep, you can see how the leaves have not opened up yet. Pic 3: The first steep. The liquor is a light yellow and the viscosity of the tea is slightly more syrupy.
Temperature of the water for most Senchas are 60-80C (140-176F) degrees, I use 70C (162F) most often.
Steeping time – the thing to look for with Sencha is when the leaves unfurl. You wish to distribute the first steep slightly before the tea has completely unfurled. At around 70C this often happens right around 45 seconds to a minute. On the second steep, the longer you steep, the more you introduce bitterness or harder undertones. You distribute the second steep after the leaves have fully opened. You can get more servings if you use shorter steeping times.
You can see in the pictures above how in this same pot of tea, the leaves have unfurled after 30 additional seconds of steep time. The liquor is darker, and isn't as syrupy as the first steep.