Those who know something about Saké usually understand that a Junmai is made from only rice, water, koji and yeast. There are no other additives, such as distilled alcohol or sugar. But, there is often a misconception on the polishing rate required for a Junmai. You might even see this misconception listed in certain books and articles about Saké, though most such literature tends to be about six or more years old.
Some people believe that a Junmai requires a seimai-buai of 70%, which means at least 30% of the rice must be polished away. That was once true, but it is no longer the case. As of January 1, 2004 the laws in Japan concerning Junmai changed, invalidating some prior information.
Now, any Saké that is made with only rice, water, koji and yeast is considered a Junmai, no matter the polishing rate. The label must simply specify the seimai-buai, the polishing rate, on it. So a Saké with a seimai-buai of only 80% can still be a Junmai. Why was this changed?
Prior to 2004, Saké breweries that produced Junmai that actually did not meet the seimai-buai requirement called it any of several different names, such as kome dake (which means “rice only”). This caused some confusion to consumers, so the new law was partially instituted to rectify that confusion.
Now, practically, you are unlikely to find much Junmai that does not have a seimai-buai of 70%, but it can and does exist. Just something to remember.