Nenryoshomai was the term for the shomai itself or the system under the Ritsuryo system which required a designated amount of white rice from the provinces to be tithed to the central government every year.
According to the Denryo, raw grain collected as So was taken to the Shoso (public repository) and considered shozei (rice tax) but part of them was refined into white rice and transported to the capital during the designated period (February to August) depending upon the province they belonged. The costs of milling and transport was paid by the farmer who paid So, but later the transport costs were paid by the government according to the Kyakushiki (regulations) of the Ministry of Popular Affairs. This was donated to the Oiryo (Bureau of Palace Kitchens under the Ministry of the Imperial Household) and used to pay the Kyokan kanjin's Jyoshoku (monthly salary). Initially, part of Denso was donated as determined by the Denryo, but after the system for storing Denso as Fudokoku (staples for an emergency) started, Suiko (government loans, often seed rice) was taken from the Doyoso Shozei (movable resource) that was allowed to be taken out by the Kunishi, part of the interest earned from this was used instead of Denso to pay for Nenryoshomai. The Shozeicho and wooden tablets found from the Heijo site have shown that this was established as a system around the Tenpyo era and donations were made in units of 5 "to" (1 hyo/pyo), and it was determined that 3 hyo/pyo per head was to be transported if using a horse.
"Engishiki" (an ancient book for codes and procedures on national rites and prayers) states that about 22 provinces surrounding Kinai and the coastal provinces donated 17,330 koku of white rice and 260 koku of mochi rice to the Oiryo (Bureau of Palace Kitchens under the Ministry of the Imperial Household), 200 koku of black rice to the Kuraryo (Bureau of Palace Storehouses) and 500 koku of black rice to the Minbusho (Ministry of Popular Affairs).