There are different suppliers throughout the game. One of them can be active and gets experience whenever you create a plate according to the points the plate got. The XP gained do get a bonus of 50% on saturdays.
Quality of suppliers determines the final stats (Volume, Taste & Aroma) of all recipes. It represents the percentage bonus to the stats. This bonus will change when suppliers are changed.
Local Grocer lv 1's quality is 10.Final recipe stats is then multipied by (100+10)%
Local Grocer lv 10's quality is 28. Final recipe stats is then multiplied by (100+28)%.