We learned in the mishna, among those liable for performing primary categories of labor: And one who salts it and one who tans it. The Gemara asks: The prohibited labor of salting is the same as the prohibited labor of tanning, i.e., salting is a stage in the tanning process.... Rabba bar Rav Huna said: One who salts meat on Shabbat to preserve it is liable due to the labor of tanning. Rava said: There is no tanning with regard to food. No action taken with food falls into this category. Rav Ashi said: And even Rabba bar Rav Huna said it falls into the category of tanning only when he needs to pack the meat for a trip and salts it thoroughly. However, to eat in the house, a person does not render his food inedible, tantamount to a piece of wood. In that case, he certainly would not salt the meat to a degree that would approximate tanning.
(ה) הַמַּפְשִׁיט מִן הָעוֹר כְּדֵי לַעֲשׂוֹת קָמֵעַ חַיָּב. וְכֵן הַמְעַבֵּד מִן הָעוֹר כְּדֵי לַעֲשׂוֹת קָמֵעַ חַיָּב. וְאֶחָד הַמּוֹלֵחַ וְאֶחָד הַמְעַבֵּד שֶׁהַמְּלִיחָה מִין עִבּוּד הוּא וְאֵין עִבּוּד בָּאֳכָלִין.
(5) A person who skins [a portion of an animal's] hide large enough to make an amulet is liable. Similarly, one who processes [a portion of an animal's] hide large enough to make an amulet is liable.
Just as one who processes [a hide is liable], so too, is one who salts [a hide], for salting is one of the methods of processing. [Prohibitions associated with the forbidden labor of] processing do not apply with regard to foodstuffs.
MISHNE LAMELECH
asks why is a verse necessary to allow salting the sacrifices on Shabbat, since they are edible and according to Rava, there is no prohibition of "tanning" in food items. He writes that he discussed this question with a great Dayan, Rabbi Yaacov Alfandari and he told him that he found a commentary on Menachot dating to the time of the Rishonim and there the same question is posed and the answer is that since the Tamid and the Musaf of Shabbat are not eaten by anyone, they are not regarded as food items and therefore the prohibition would have applied. JHence the verse was necessary.
MAHARAM OF ROTTENBURG
raises the same question and provides a different answer. The issue is the burning of the salt and thus it may have been included in the prohibition. Hence, the need for the verse.