The Rabbinical prohibition of squeezing fruits and the cases in which it is permitted even initially
Squeezing edible fruits on Shabbos for the purpose of drinking their juice:
A. Strawberries, pomegranates and all fruits which are squeezed when there are plenty of them:
Rabbinically it is forbidden to squeeze even strawberries and pomegranates in order to drink their liquid.
The reason for this is: due to there being segment of people which have a large amount of strawberries and pomegranates and they squeeze them for their juice just like [is done with] olives and grapes [See Q&A], and if other people also had such a large amount of [these fruits] then they too would be accustomed to squeeze it for its juice. Therefore anyone who squeezes them for the sake of its juice these thoughts of his help give [the juice] a liquid status Rabbinically, as we do not claim that [the persons thoughts of using the fruits for juice] is nullified in face of the [intended use of this fruit by the] populace.
Pears and other fruits: Similarly those pears (that we call brenis) which are common to squeeze for their juice in certain places, is forbidden to squeeze on Shabbos for the entire [populace of the] world, because it is possible that if the entire world had as much of these [pears] as the other places do, then they too would squeeze the pears for their juice. The same law applies for all fruits of the sort.
B. Edible fruits that are never squeezed for juice even when they have a lot of the fruit: 
All other [edible] fruits which are not common for [people of] the world to squeeze for their juice, to drink their liquids to quench their thirst or for pleasure, even if they have a lot of them, then even if they are commonly squeezed for medicine they do not have the status of juice due to this even Rabbinically and is [thus] allowed to be squeezed on Shabbos, as it is like separating food from food.
Now although that this person who wants to squeeze them intends to do so for their juice, nevertheless his intentions are nullified in face of the [common practice] worldwide.
Fruits which are squeezed for juice in ones area but not in others: Nevertheless in any area where the custom is to squeeze a certain fruit for its juice then its laws in that area are the same as the laws of strawberries and pomegranates and is thus forbidden to squeeze it in those places for their juice, because the intent of this [person] that wants to squeeze it is not nullified [to the world custom] since all the people of his area do this during the week. However other places are allowed to squeeze them since they are not accustomed to squeeze them for their juice even if they have a lot of the [fruit].
There are opinions which say that all fruits are Rabbinically forbidden to squeeze for the sake of their juice, as since the person squeezing it intends to do so in order drink the juice to quench his thirst or for pleasure (or even for healing) therefore they are Rabbinically considered [the status of] juice, and we do not say that his intentions are nullified in face of the worldly custom. (However if ones intention [in squeezing] is in order to give flavor to a food then it is allowed [according to all opinions] as will be explained in Halacha 3B).
The Final Ruling:
The custom in many places is to be stringent [like this latter opinion] although the main Halachic opinion is like the first opinion. Nevertheless in a place where the custom is to be stringent one may not do differently. [Practically, there is no known place today that is particular like the stringent opinion to never squeeze a fruit to drink its juice even if it is never commonly squeezed.]
C. Fruits which are commonly squeezed but which their juices are not commonly drunk plain:
Apples and lemons: Apples have the same law as other fruits [which are not commonly squeezed anywhere]. [Furthermore] even lemons do not have the same laws as strawberries and pomegranates, but rather like other fruits. [Therefore they] are allowed to be squeezed for the need of their juices even for the sake of drinking [the juice, as opposed to using it for other purposes,] according to those opinions which permit [doing so to fruits that are never squeezed for their juice].  According to those opinions who forbid [squeezing any fruit for the sake of drinking their juice] it is at the very least allowed to squeeze them for the need of food, meaning in order to flavor the food with their liquids and the like. [See Q&A regarding the ruling today if one may squeeze lemon]
The Reason: Now, although that in those places that there are plenty of these fruits they [are accustomed to] squeeze them for their juices, [nevertheless] they do not receive the same laws as strawberries and pomegranates just because of this, even in those places [that squeeze them]. [The reason for this is] because they do not squeeze their liquid for the sake of drinking it but rather for the sake of using for [flavoring] food. [Furthermore,] even if they are accustomed to squeeze the [juice] into water in order to drink, it is allowed since it is not common to drink them plain [in their concentrated state].
D. Squeezing juice from inedible fruits:
The above is only referring to fruits which are fit to be eaten however fruits which are not fit to be eaten are forbidden to be squeezed according to all opinions even into food [and certainly not in order to drink their juice].
See above Halacha 1B.
Summary-Squeezing fruits for the purpose of drinking their juice:
1. The Rabbinical prohibition:
It is Rabbinically forbidden to squeeze juice from fruits in the following cases:
-Fruits which are commonly squeezed for their juice when one possesses much of that fruit: It is Rabbinically forbidden to squeeze them anywhere in the world.
-Fruits which are not commonly squeezed for juices even when possessing much of them but in ones city it is common to do so: Then it is Rabbinically forbidden to be squeezed in that city. Regarding other cities, this will be explained below under the permitted cases.
Fruits which are not currently edible: Are [possibly Biblically] forbidden to be squeezed even into food, and certainly not in order to drink, no matter what type of fruit it is.
2. The Permitted cases:
All edible fruits which are not commonly squeezed for their juice throughout the world [see below for definition] even when possessing much of them, and are not squeezed in one’s city, may be squeezed on Shabbos even for their juice. However in an area where people are stringent to not squeeze any fruits for their juice, one may not change from their custom and may thus not squeeze juice to drink even for medicinal purposes. [Practically, there is no known place today that is particular like the stringent opinion to never squeeze a fruit to drink its juice even if it is never commonly squeezed.]
3. The definition of “squeezed for its juice”:
The rule: Only fruits which are 1) commonly squeezed in order to drink their juice plain and 2) are drank in order to quench one’s thirst, or for mere pleasure, are defined as “squeezed for their juice”.
Juice which is not commonly drunk in its concentrated form: If a fruit is not commonly squeezed to drink its juice in its concentrated state even when there is plentiful of it, then even if it is commonly squeezed to season foods, or to be used as concentrate, and have liquid added to them, nevertheless it has a definition of a fruit that is not commonly squeezed.
Juice which is commonly drunk as medicine: A fruit which is not commonly squeezed to drink its juice to quench ones thirst or for mere pleasure but rather to drink as medicine has a definition of a fruit which is not commonly squeezed.
Final Summary-It is only permitted to squeeze fruits for their juice if the following 4 conditions are met:
- The fruit is edible in its current raw state.
- The fruit is not commonly squeezed for its juice by people around the world even if they were to have plentiful of it.
- The fruit is not accustomed to be squeezed for its juice in one’s city.
- It is not the custom in ones city to be stringent and always prohibit the squeezing of fruits even when all the above conditions are met.
May one squeeze juice out from crushed fruits:
Grapes and olives: Doing so is Rabinically forbidden.
If one is unsure whether a certain fruit is commonly squeezed to drink its juice, when there is plenty of that fruit available, is it still forbidden to squeeze it due to doubt?
No. A fruit only is prohibited to be squeezed if one knows for certain that there are places which squeeze the fruit when there is plenty of it.
If in ones city a fruit is not squeezed for its juice despite there being plentiful of it, may one squeeze the juice on Shabbos even if the rest of the world does squeeze it for juice?
Yes. However this is only applies if they do not sell these juices in stores of that city, as will be explained next.
If a fruit is only squeezed for its juice within factories and then sold in one’s city, while in one’s private home they do not squeeze it for its juice even when there is plenty of it, is it nevertheless considered commonly squeezed and thus forbidden to squeeze on Shabbos?
Yes. So long as the fruits are commonly squeezed in factories and bought by the populace they are considered commonly squeezed. As a result of this, being that today many different fruits are squeezed in different parts of the world and their juice is then sold in ones city, all the fruits of these juices are forbidden to be squeezed.
Practically which fruits today are forbidden to squeeze?
In truth, today majority of fruits are forbidden to squeeze, as majority of fruits are commonly squeezed to drink their juice somewhere in the world and are then sold in ones city for drinking [see previous Q&A].
The following is a partial list of fruits that are forbidden to be squeezed on Shabbos in order to drink their juice, being that they are commonly squeezed for juice when they are in plentiful. This list is not all inclusive and may include other fruits as well.
- Apples: Today, apples are forbidden to be squeezed for their juice.
- Citric fruits such as oranges/grapefruit:  Are forbidden to be squeezed on Shabbos for their juice being that they are commonly squeezed in today’s times in order to drink their juice.
- Lemons: One is to be stringent to avoid squeezing them for their juice. Regarding if one may squeeze lemons into water or food, see Halacha 3 Q&A there.
- Watermelon, cantaloupe, honey dew, apricot, seemingly are not commonly juiced but they are juiced in juice stores and hence perhaps are forbidden to be squeezed.
May one use a juicer to squeeze fruits that are permitted to be squeezed?
No. It is only permitted to do so using ones hands, being that using a specified vessel is a mundane act which defiles the sanctity of Shabbos.
May one use a spoon to eat a fruit that may not be squeezed, such as a grapefruit?
Being that doing so causes juice to be squeezed out from the fruit this poses a problem of squeezing, and carries the following laws.
-Intends to drink the juice: If at the time of using the spoon one intends to drink the juice which squeezes out, then it is forbidden according to all opinions to eat the fruit with a spoon, being that this is exactly similar to initially squeezing a fruit for its juice.
-Does not intend to drink the juice: If however one does not have any intent to squeeze out juice and tries his best not to do so then there are Poskim which have been lenient to allow one to use a spoon even though it is impossible to completely avoid the squeezing of any juice. Nevertheless, even in this case it is proper to be stringent being that the squeezing is inevitable.
May one cut a fruit which may not be squeezed if in the process juice will squeeze out, as is common with citric fruits?
If the juice that is squeezed out will go to waste it is allowed. This applies whether the juice goes directly to waste, such as when cutting directly on the counter, or if he plans to throw it out, such as when one is cutting on a plate.
If however one intends to drink the juice it is forbidden to cut it.
May one squeeze out the juice of a fruit for no need at all but rather simply out of habit or the like?
If doing so does not benefit the fruit and the juice will go to waste then many Poskim are lenient to allow it by all fruits other than grapes and olives. However, the Tzemach Tzedek, along with other Poskim forbid this.
If a food will only become edible due to the squeezing may it nevertheless be squeezed?
No, as this poses a Borer prohibition. This may not be done in any cases, whether with intent to squeeze the liquid into food or to sweeten it.
 So rules Magen Avraham and Mishneh Berurah .
 So rules the Ketzos Hashulchan 126 [footnote 20] and other Poskim; Shabbos Kihalacha Vol. 2 p. 401;
 The Yaavetz, as well as the Tzemach Tzedek bring many arguments against this leniency of lemons, and thus side to forbid it.
So rules Ketzos Hashulchan 126 footnote 25.
 Meaning even according to the opinion which holds that fruits which are not commonly squeezed may be squeezed for their juice. However as mentioned above in 1B there is an opinion which rules that squeezing inedible foods has the same law as edible foods. Admur ruled that one is to be stringent.
 See 3 for the definition
 See Ketzos Hashulchan 126 footnote 20. And Shabbos Kehalacha Vol 2 page 400.
 So rules the Ketzos Hashulchan 126 [footnote 20] and other Poskim; Shabbos Kihalacha Vol. 2 p. 401;
 Shabbos Kehalacha Vol. 2 p. 392
 Shabbos Kehalacha Vol. 2 p. 394
 As the prohibition of squeezing commonly squeezed fruits is only due to the fact that we say perhaps if there were to be plenty of a given fruit in ones city then they too would drink its juice. Thus here where it is clearly evident that despite their abundance they do not drink its juice, therefore it is allowed.
 Shabbos Kehalacha Vol. 2 p. 394
 Shabbos Kehalacha Vol. 2 p. 392-394
 Shabbos Kehalacha Vol. 2 p. 393
 So rules Mishneh Berurah in Biur Halacha based on Chayeh Adam. And so rules Rav Farkash in Vol. 2 p. 392
 Although Admur rules like the Taz that apples are permitted to be squeezed, nevertheless this was back then when apples were never commonly squeezed to drink their juice plain. However today that this is done, then certainly they too agree that it is forbidden.
 So rules the Ketzos Hashulchan [126/6
 Shabbos Kehalacha Vol. 2 p. 404
 Although lemons are not considered fruits that are commonly squeezed to drink their juice plain and thus from the letter of the law may be squeezed even for their juice, nevertheless today one is to be stringent regarding lemons like those opinions which forbid squeezing them.
So rules Ketzos Hashulchan 126 footnote 25. The Yaavetz, as well as the Tzemach Tzedek bring many arguments against the leniency of lemons, and thus side to forbid it.
 Shabbos Kehalacha Vol. 2 p. 396
 So rules Ketzos Hashulchan 126 footnote 19
 Shabbos Kehalacha Vol. 2 p. 408-410
 So rules Ketzos Hashulchan 126 footnote 14, SSH”K 5/12, Yalkut Yosef
 Rav SZ”A in SSH”K 5/12
 It’s said that Rav SZ”A later retracted the ruling in SSH”K due to reasons of Psik Reisha Velo Yamus.
 Shabbos Kehalacha 15/17
 Shabbos Kehalacha Vol. 2 p. 420
 Shabbos Kehalacha Vol. 2 p. 446
 So rules Tehila Ledavid 320/14