ym: "Sarashina means it is 100% made from only the very core part of the buckwheat, where it contains the most sweetness. As in a normal soba, flour would be used as an addition (called tsunagi) to blend that sweetness.
Also note there are two types of soba-tsuyu (dip sauce). According to the master, the tsuyu is where the extra investment is made, and it uses a 10 year vintage tsuyu base.
No wonder the difference.
A soba-connoisseur would first realize that the scent of the tsuyu is different, and then the harmony of it with the sarashina soba."
They even disclose theingredients - which is rare for a business of such old standing (since 1789)."