The twenty-second perek of Massekhet Shabbat begins on today’s daf and its main concern revolves around different types of prohibitions subsumed under the category of shevut (=a Rabbinic prohibition). Here, too, there is no single theme that unites all the topics addressed, although most of them deal with food preparation on Shabbat.
One of these issues relates to the laws of squeezing on Shabbat. Squeezing is not listed as a primary category of prohibited labor. Its prohibition is not based on the act of squeezing alone; indeed, squeezing can be a subcategory of at least two primary categories of labor, depending on the circumstances: It can be a subcategory of the labor of threshing, which is defined abstractly as removing the desired contents from within an unwanted wrapping or shell, and it can be a subcategory of the labor of whitening, when the squeezing is performed in the process of washing.
The relationship between squeezing and threshing is not completely clear and uniform. For example, in the practical discussions regarding milking animals on Shabbat, the question arises as to the extent to which one should understand milking as a form or subcategory of squeezing or threshing. This leads to the question of whether milking should be viewed as a Torah prohibition or a rabbinic decree. Similarly, it is necessary to delineate the fine differences between types of squeezing that can be viewed as a subcategory of threshing and other types of squeezing that are externally similar to the first type but differ with regard to the intent of the person squeezing or the purpose of the act itself.
One of the cases that appear in the first Mishna is this law:
One may not squeeze fruits on Shabbat in order to extract liquids from them. And if liquids seeped out on their own, it is prohibited to use them on Shabbat. Rabbi Yehuda says: If the fruits were designated for eating, the liquid that seeps from them on Shabbat is permitted. There is no concern lest one purposely squeeze liquids from fruit that is designated for eating. And if the fruits were originally designated for liquids, the liquids that seep from them on Shabbat are prohibited.