"Moro-haku" ("moro" means both sides, and "haku" means polishing) was the name of a sake brewing method which used polished rice for both the "koji-mai" (the rice in which the mold of "koji" [Aspergillus oryzae] was cultivated) and the "kake-mai" (also called "fukashi," meaning the steamed rice).
It also meant highly clear sake, made according to the above-mentioned method, which is almost equivalent to today's "seishu" (refined sake).
Conversely, the brewing method using unpolished rice for the koji-mai and polished rice for the kake-mai, as well as the sake made using this method, were both called "kata-haku" ("kata" means one side). The brewing method using unpolished rice for both the koji-mai and the kake-mai, as well as the sake made using this method, were both called "namizake."
The origin of moro-haku was "soboshu" (monk's sake) which was brewed at major temples in Nara during the Heian period. The brewing method descended to some brewers in Nara, and they produced "nanto moro-haku," which enjoyed a reputation as the highest grade clean sake for a long time, just like today's "junmai daiginjo" (added alcohol-free "daiginjo" [top-quality sake brewed at low temperatures from rice grains milled to 50% of weight or less]).
From the Muromachi period, it became that many sake brands with names consisting of the production district and the term "moro-haku" were produced throughout the Kinki region in places such as Sakai, Tennoji and Kyoto. In the Edo period, the moro-haku transported from "Kamigata" (Kyoto and Osaka area) down to Edo was called "kudari moro-haku."
The word "moro-haku" was included in the Japanese-Portuguese dictionary compiled in 1603 by missionaries of the Society of Jesus who came to Japan to propagate Christianity, and the meaning was explained as the highly valued sake produced in Nara. But the dictionary did not go so far as to describe the brewing method used to produce moro-haku. This word was also translated from Portuguese into Spanish.
During the Edo period, there was no legislated sake grading system like that which existed in the Showa period, but consumers roughly ranked sake as shown below.
Ranking sake in this way well known and led to little doubt.
Naturally, the development of moro-haku brewing techniques have been closely related to rice polishing techniques. Until the early Edo period, rice was polished with a millstone and a mallet, or with a foot Chinese millstone at best, so the rice polishing ratio (the percentage of weight remaining after polishing) in those days was far less than today, when rice polishing makes it possible to produce high-quality sake, including "ginjoshu" (sake brewed at low temperatures from rice grains milled to 60% of weight or less).
However in the late Edo period, a high-grade rice polishing technique was devised in Nada-Gogo, which enabled large-scale polishing with a waterwheel, and the technique pushed Nada above Itami and Ikeda (the advanced sake producing districts) in terms of sake quality.