Niconico News covers a bubbly sake product, but maybe not the one you were expecting. It's sake soap.
The Mutenka Sekken (無添加石鹸, literally "soap with no additives") brand from the 63 year old Marubishi Sekken company uses traditional Japanese ingredients such as rice bran, yomogi Japanese mugwort, yuzu, green tea, cherry blossoms, cypress... and sake, specifically from the Fukuju brewery in Kobe.
The soap is made in the city of Miki, not far from Fukuju and other breweries in Hyogo Prefecture. Everything is made by hand using one of two traditional manufacturing processes, one in a kama or cauldron and another called "cold" as it doesn't use heat.
The kama method sees all the ingredients put into a large cauldron which is then heated gently by a wood fire for three days. The soap is then allowed to dry and mature, so the process takes between 90 and 180 days from start to finish.
The cold process makes soap from oil without using heat, a tricky process where instructions have to be followed closely to yield a soap that makes the most of its nutritious ingredients. The oil is converted into soap by adding an alkali which causes a reaction known as saponification that transforms the liquid over time into a solid suitable for a bar of soap.
As of 26 June 2018, the Kobe sake soap with Fukuju sake was the number one best-selling soap on the site. (And if someone can make any product that smells like a fermenting moromi, I'll take it in bulk.)