Merchandise Manufactured During Shabbos
We are not permitted to cook foods during Shabbos. If a Jew desecrates Shabbos by cooking, our Sages imposed various penalties upon the people who cooked it and those for whom it was cooked. However, the food is in essence Kosher. and unlike actual non-Kosher foods, which when cooked in a pot make the pot non-Kosher, foods cooked during Shabbos do not make the pots they are cooked in not Kosher.
It is a tragedy when any Yid fails to appreciate our being Gd's Chosen People, and that our National Heritage, History and Culture is Gd's blessing.
We loyalists understand that had we truly appreciated Torah and our relationship with Gd, our enthusiasm and love would inspire all Yidden to love and treasure what we love and treasure.
Take Shabbos as an example, which is singled out as a Sign that testifies to our special relationship with HKBH; we must mourn those who are yet to appreciate its value but the process for correction is in our hands.
When Shabbos is desecrated on behalf of others, the Magen Avraham, asserting the principle that people do not sin for the benefit of others, Paskens that no penalty is applied and the the food may be eaten immediately at the conclusion of Shabbos.
However, the Ksav Sofer (O.C. 50) reasons that in the case of an eatery for example, where there is ultimately benefit to the Jewish owner, the food is banned until such time that benefit is not derived from the work that was performed during Shabbos.
If the food served Saturday night is likely prepared during Shabbos, then if a significant proportion of Saturday night customers are Jewish, they should not eat at all on Saturday night, even after a suitable time has elapsed, since they are thereby likely to be the beneficiaries desecration of Shabbos.
We are not permitted to perform Melachah during Shabbos.
Chazal, in order to maintain the sanctity of Shabbos and its prohibited activities, impose a range of penalties upon the products that are processed in violation of Shabbos. There are a number of variables that govern the penalty and its range:
* was it a deliberate or inadvertent violation,
* the penalty may be permanent or only for the duration of Shabbos,
* its restriction may be universal or limited to those who violated Shabbos and for whom Shabbos was violated,
* it may ban only the product or even benefits derived from it.
Sh"A O"Ch 318:1
One who processes an item on Shabbos, in deliberate violation of its laws, may never use that item. Others however, may use that item at the conclusion of Shabbos, even those for whom the violator produced that product [MBerruah 318:5]
Furthermore, the MBerrurah  explains that the prohibition applies exclusively to the actual item, it may however be sold, even by the violator, in order to benefit from that sale.
Those who violate Shabbos by cooking, face an additional issue; the foods that were cooked during Shabbos are absorbed in the utensils. When this is a knowing deliberate violation of Shabbos, and the food may never be used by the violator, does the prohibition apply to the utensils which have absorbed those foods or perhaps that absorbed flavour is not the food itself but akin to the sale value of the food and therefore permitted?
The Magen Avraham [quoted in the MBerrurah] understands from the RaShBA that the food flavour absorbed in the utensils is equivalent to the food itself and therefore the violator [who has now repented] must Kasher the utensils. If not Kashered, the flavour of the prohibited Shabbos violation food, which has penetrated the utensils, will add discernible flavour to other foods.
Firstly, this flavour is deemed to be viable only for 24 hours max, after which it becomes tainted and is of no consequence.
Secondly, when the mass of the food is more that 60 times the mass of the utensil, Halacha asserts that even if all the non-Kosher absorbed in the utensil is injected into the food, it is not discernible and is of no consequence.
Thirdly, this ban applies exclusively to the violator, others may use the foods and most certainly the utensils, and the foods cooked with those utensils, even by the violator.
Fourthly, since the violator may legitimately sell the food cooked on Shabbos, it is undeniable that and the utensils themselves may be used by others.
There is a further complication - the absorbed flavour becomes tainted after 24 hours and is deemed to spoil whatever it contributes to i.e. it cannot make food cooked in that pot non-Kosher. Our Sages nonetheless decreed that the utensils must be Kashered otherwise we would use one pot for both dairy and meat - Mon Tues and Wed for dairy, Friday and Shabbos for meat.
Might this same ruling that requires Kashering apply to the Shabbos cooked food absorbed in the utensils in spite of it being tainted?
The Rashba [Teshuvos 1:175] Paskens that when performing the Mitzvah of cooking on Shabbos where it is medically required, there is no need to Kasher the utensils after Shabbos. At the conclusion of Shabbos, even the food is permitted for all. If the food was not banned during Shabbos, one might be tempted to add a little for others who have no medical need. The Magen Avraham [318:1 cited by the MBerurah 318:4] thereby derives that if the cooking was prohibited, the pot does require Kashering.
The RashBa and MAvraham are misunderstood by those who suggest their ruling equates a pot that has been knowingly used to cook in violation of Shabbos Law, with a pot used for cooking non-Kosher food.
It is quite clear in the Mishnah Berurah - this pot may not be used by THIS person for HIS food. The reason: the food is Kosher, banned by a Rabbinic penalty directed against he who violated Shabbos that bans him from eating that food. Other Jews may eat it. The Shabbos desecration does not convert Kosher food into non-Kosher food.
The RaShBA's Pesak, as explained by the MAvraham, can be described as being limited, not universal; meaning the food and so too the food flavour absorbed in the pot, is prohibited to HIM alone but to no one else. He may not cook with that pot but anyone else may. There is no prohibition preventing other people from using that pot even in the first instance. This is Paskened LeHalacha by Rabbi Zoldan [Nesiv Hachalav, p. 84, published by Tenuvah]
Other Poskim disagree entirely with the Magen Avraham's deduction from the RaShBa. They argue that only non-Kosher food has the power to create prohibited absorbed flavours that require Kashering [Yad Yehuda, YD 99:18]