Feb 6, 2016, 14:15
There is no hard fast rule, this takes some time and practice to perfect. However, I just made a nice bowl of that using 2 scoops from a traditional Japanese bamboo teaspoon. This came out to 2.5 grams. It took 55 mL of hot water to make it just right, so that would come out to 22 mL of hot water per gram of matcha. That being the case, if you wish to use 70mL, you would use about 3 grams of matcha for that.
As for the temperature, I think your temperature is a bit low. I use 90℃ water to first heat my bowl, and also to pre-wet my whisk. Then I dry off the bowl, add the matcha, then again I use 90℃ poured into a small teacup first to add to the matcha bowl. Of course the water cools down a bit from 90℃ as you transfer between vessels. Whisk vigorously, you should be able to obtain a nice green foam on top. If you don't, it probably means either you used too much water, you didn't pre-heat your bowl, or maybe both. Practice makes perfect!