Factorio Forums

Food insertion has priority over ingredient insertion. You can't filter the food slot to only accept common nutrient. You can't use circuits to detect empty food slot because "read contents" does not provide food information. Can't use circuits for timing (i.e. always swing food providing inserter 1 tick before inserter providing inserter) because it's a potential race. Basically there is no 100%-proof way to ensure ingredient is not inserted as food.

I consider this a bug. Potential solution could involve either adding food item to "read contents", adding a separate signal for "food contents", or allowing a filter on food. Though any solution that's not a slot filter is potentially racy.

Suggestion that is exactly this :
viewtopic.php?f=6&t=118631