How much culture to use

How much culture should be used for 3litres of milk?

Hi
On the package is wrriten 1 sachet = 1L,so 3L = 3 sachets
Please note that the amount of milk increase the incubation time and we recommend to use
1 sachet and 1L of milk for the activation of the first batch and then to use 1-2 spoons of ready yoghurt and reculture larger amount of milk
Please find video explainers here: https://www.youtube.com/c/NPSelection/videos