But the traditional method of aging awamori, known as "shitsugi," is very curious and does not boast a high degree of repeatability. To explain it, we need to bear in mind that hundreds of years ago, when the Ryukyu kingdom was in its heyday, folks would have several lidded urns of awamori lined up outside the house. The urn containing the oldest awamori was closest to the door, with each urn having successively younger product inside.
When a drink was ladled out from the first urn, the amount taken was then replaced with awamori from the second urn. This in turn was refilled from the third urn and so on. Freshly distilled stuff was placed into the last urn when ready. This led to each urn having inside of it an indeterminable blend of awamori of different degrees of aging. So although kusu refers to aged awamori, traditionally it was not really possible to be any more precise than that.