Cases which contain the Borer prohibition

A. Making cheese on Shabbos[1]     

Making the curd: One who curds [milk], in which he takes milk and places a stomach [or other enzyme] into it in order to curd[2] it, is liable for separating because he has separated the curd from the milk.

Placing the curd into a strainer: Similarly, if one places the curd into an elastic vessel[3] and the whey drips from inside it then this is an offshoot of separating food from waste through using a sieve and sifter and one is thus liable.

The reason: Now, although the curd and the milk are both a single species of food and there is [thus] no waste [here] at all, nevertheless since they are liquid substances which mix well which he is [now] separating, therefore this contains the separating [prohibition] just like one who is separating food from waste.

Making hard cheese:[4]  If one solidified [curd] and turned it into cheese he is liable for building.

The reason for this is: [5] because anyone who gathers parts [of an item] to each other and bonds them together until they become a single substance has [transgressed] an offshoot of [the] building [prohibition].



May one place lemon into milk on Shabbos to turn it into cheese?[6]



May one place milk in a hot area on Shabbos in order to turn it into cheese?[7]



B. Removing seeds and nuts from honey:[8]

One may place sesame and nuts into honey, although he may not [gather them[9] and] separate them with his hands [as doing so is considered separating[10]].


C. Catalyzing beverages on Shabbos[11]

It is forbidden to place dregs into beverages in order to catalyze it even though [the liquid] is already fit to be drank on Shabbos being that through doing so one causes the dregs of the liquid itself to sink to the bottom of the vessel it is an offshoot of separating similar to one who curds milk.


[1] 319/25

[2] Cheese is made by separating the milk into solid [3] This refers to a vessel made of material that can be stretched out do to having tiny holes in it, and thus allows the milk to drip out. Similar to a plastic bag.

[4] 319/26

[5] 319/26

[6] Shabbos Kehalacha Vol. 2 p. 176

[7] Shabbos Kehalacha Vol. 2 p. 176

[8] 319/27

[9] Mishneh Berurah on 319/66

[10] Mishneh Berurah on 340/11

[11] 319/29

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