Matsuai makes this shoyu from its flagship Marudaizu Koikuchi Shoyu. This shoyu is aged ten years in refrigerated storage. The long maturation produces deep, layered flavors and aromas. The long aging time also makes this shoyu thick like syrup. It is a "koikuchi," dark style shoyu. The soy beans and wheat are grown by contract farmers in Kumamoto who do not use any pesticides or chemical fertilizers, which is Matsuai's policy.