food has been deemed war material since the War of the Austrian Succession when the modern definition of blockades were established. Changing that would change every single war after that such that ww1 would be butterflied.
In 1900 Russia publicly declared a list of contraband of war. Food was not on it. That said Russia declared food unconditionally contraband during the Russian Japanese war. Britain protested.
In 1884 during the Franco Chinese war France declared food a contraband and Britain protested.
In 1909 naval conference between the great powers food was declared conditionally contraband. This meant that food was contraband but neutrals had to be paid for food seized.
I guess we are looking for a different naval conference of 1909 for a pod?