Are Avocado pits Muktzah on Shabbos? Can they be used to prevent browning?
In general, all pits that are inedible, and are not designated to be eaten by local house pets and farm animals, are Muktzah. The question however is asked regarding avocado pits being that they are commonly reused to prevent the avocado from browning. Practically, the following is the law: If one removed the avocado pit from the avocado before Shabbos, and designated it to be used to prevent the avocado dip from browning, then it is not considered Muktzah. If, however, they were removed on Shabbos itself, then as soon as they are separated from the fruit, it is best for it to be immediately discarded and treated as Muktzah just like all other pits. If one only desires to use half of the avocado, then there is no problem with leaving the pit in the other half, so long as it is not removed and then replaced on Shabbos. It is interesting to note, that scientifically in truth avocado pits indeed do not help to prevent browning with exception to the area directly under the pit, and simply using an airtight container is one’s best solution.
 See SSH”K 16:10 and Piskeiy Teshuvos 308:43 regarding apricot pits that they are Muktzah unless designated to be used for children games before Shabbos. However possibly for children themselves they are not Muktzah even when removed on Shabbos. [SSH”K ibid footnote 33] However, majority of Michabrei Zemaneinu rule that it is Muktzah if removed on Shabbos. [Piskeiy Teshuvos ibid footnote 359]
 Admur 308:8; 308:60; Michaber 308:27
 As a) The pit will be thrown out afterwards and is hence considered permanently designated for this purpose, in which case we rule that this form of designation before Shabbos removes its Muktzah status. [Admur 308:53; Michaber 308:22; Ketzos Hashulchan 110:5] b) It is common to use the pit for this purpose and hence follows the law that even if it is designated before Shabbos only for a limited amount of time for a common purpose, its Muktzah status is revoked. [Admur 308:36 [regarding if used in the past]; 50-51 and 53 [regarding both if used in the past or designated for temporary use]; 1st opinion in Michaber 308:22; Biur Halacha 308:22 “Beyichud” that using in past has same law as temporarily designating]
 On the one hand one can argue that even when it is separated on Shabbos it should not be considered Muktzah as a) there is still some fruit that always remains on the pit which one may want to eat and b) it is customary by many to use it right away to place in the dip to prevent browning and hence perhaps it should be considered an automatic designated vessel until one decides to throw it in the garbage. This would perhaps follow the same law as Shivrei Keilim, in which we rule that since they were originally a non-Muktzah vessel if it remains fit to cover a vessel, then it is not Muktzah even though it has yet to be designated for this purpose. [Admur 308:24; Michaber 308:6; Mishneh Shabbos 124b] Perhaps one can apply the same argument here that since it was originally attached to a fruit and not Muktzah, so too here as well, since it still retains a common use, therefore it is not Muktzah on Shabbos. Furthermore, one can argue that since the moment one detaches the pit from the fruit he intends to reuse it to prevent browning, it never goes to a moment in which it is considered a non-designated item which is Muktzah. [See Admur 308:50 regarding Palm branches that we follow one’s intent at the time that it was removed from the tree] On the other hand one can argue that the majority of pits are not saved and are rather thrown out right away, and hence the fact that some fruit may remain on it, and that some pits are used to prevent browning don’t turn it into an automatic designation. Vetzaruch Iyun and practically one is to be stringent, although perhaps those who are lenient do not have to be protested, as rules SSH”K regarding apricot pits.