Email from Florent of Thes du Japon (keep in mind, he is French and thus his English though very understandable is not perfect):
I think it's important to clarify the japanese steaming words stuff.
The traditional and unique steaming method until the 60's is steaming leaves 20-30 seconds.
That's what is said asamushi or futsumushi. But "asamushi" is more used because it is easier to understand for people. But "futsumushi" is the word which was choose officially for the minister, competitions, Japanese tea instructors Association, etc.
Originally, "fukamushi" was a new steaming method born in the late 50's, but its real development began in the late 60's.
"fukamushi" means "deep steamed" and "asamushi" means "not deep steamed". "futsumushi" which is used for the same method as Asamushi means "normal, or usual steamed". Of course, the opposition between the adjectives "Asai" (not deep) and "fukai" (deep) is really easy to understand for the average customer, but asamushi/futsumushi producers (especially in the Kansai area) where very worried about the word "not deep" ("asai" in Japanese can be consider as negative), they claim that this is not "not deep", because steaming leaves 20-30 is the traditionnal method used since the beginning for steamed leaves tea, this is normal. For this reason, the word "futsumushi" was officially choose.
Myself, personally, and also as a Japanese Tea Instructor, I completely agree with this point, the adjectives "asai" if not appropriate, and I prefer to use the official word, Futsumushi.
But in reality, the word "asamushi" is still most used and understood.
The problem become more complicated when the "middle steamed" (chu mushi) nuance appears. In competition or other, there is no "chumushi" category. All teas that are steamed more than the futsumushi (= asamushi, alright) 30s are fukamushi.
Originally, fukamushi where steamed about 1min. But progressively, appeared teas steamed 1min30, 2min, and now even more !! So, a one minute steamed teas is quite different than a 2mn steamed one. 2min steamed become a fuka, one min steamed one a Chumushi. But there is no real rule for this nuance. The frontier between chu and fuka is unclear and subjective.
But it can become even more complicated, when some vendors decide to use "futsumushi" instead of "chumushi" !
As a result you have 3 naming patterns,
The official one (which I use)
futsumushi - fukamushi
The most used one
asamushi - chumushi - fukamushi
the tricky one
asamushi - futsumushi - fukamushi
I hope my explanations could help to clarify...
Also , there is the naming i heard from a grower in Shizuoka mountains:
dento mushi (traditional steamed) (=asamushi/futsumushi) - yobun mushi (too much steamed). Of course this half serious half a joke.