Processed food with same nutritional value and even same recipe sometimes will not stack.
Specifically, this seems to happen when one batch already existed when loading a savegame, and the other batch has been created during the current session.
Saving and reloading fixes the issue, so that the batches will stack.
(My guess would be that the internal numerical format and the savegame numerical format differ, leading the saved-and-reloaded batch to have a slightly different value due to rounding effects.)
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