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1. The Biblically forbidden forms of cooking:
A. The Principal prohibition:
Cooking [on Shabbos] is one of the Principal [forbidden] actions, being that in the Tabernacle [colored] herbs would be cooked in order to use their dye.
B. The forms of cooking:
Frying, baking and roasting: Not only is cooking in water alone included [in this prohibition], but even frying, and baking and roasting, are included in [the] cooking [prohibition].
Melting and hardening materials: As well anyone which has melted a hard item with fire, such as one who softens one of the types of metals, or heats up the metal until it becomes [as red as] a coal, or melts wax or fat or tar and sulfur with fire, or hardens a soft material with fire, such as one who places clay vessels in fire until it becomes an earthenware vessel, he is liable for cooking. [See Q&A 1-5]
Does the prohibition to soften or harden a non-food item apply even if he does not have intent to do so and it inevitably occurs?
No. The Melacha of softening metal and the like only applies when one intends to do so, and thus even if it will inevitably occur, if this occurs against ones will it does not contain a prohibition.
May one pour boiling water into a plastic cup if it will cause it to melt?
Yes, it is allowed.
Is melting/softening an object to less than Yad Soledes forbidden?
If the item can only be melted with the heat of Yad Soledes then even if it itself was not heated to that point one is nevertheless liable. However if it melted through heat that is less than Yad Soledes it is not prohibited.
Is the prohibition to soften an object applicable also by food, such as to place bread or Matzah in soup and the like?
· Foods which would only soften with hot water: Some Poskim rule that softening a hard item through heat is forbidden due to Bishul. Thus, one may not place bread in hot water. Others rule that if the food is already fully cooked there is no prohibition involved in doing so. Practically one may be lenient in all cases that the food was already cooked. Some Poskim rule regarding butter that it is forbidden to melt it despite being previously cooked, due to softening a hard item.
· Foods which would soften with even cold water: The prohibition of softening a hard food does not apply by foods which would soften even with cold water, such as bread and crackers and the like. However some Poskim are stringent even in such a case.
· Melting foods: According to the Alter Rebbe in the Siddur it is forbidden to melt all substances near a fire due to Bishul, in addition to a possible Molid prohibition. See Halacha 8]
· Foods which harden due to hot water: The prohibition of hardening a soft food such as an egg, contains the prohibition of hardening a soft substance.
May one toast bread near a fire on Shabbos or is this considered forbidden due to hardening a soft object?
1. Question: [Thursday, 11th Elul, 5781]
Is there any problem for me to place my Challahs on the Blech on Shabbos for them to become toasty?
It depends on how you plan on doing so. If the Challah is dry and you place it on top of a pot that is on the left fire or Blech just for it to warm up and not become actual toast, then it is permitted to be done. If, however, the Challah contains liquid such as condensation or ice particles from the freezer, then it must be dryed prior to heating it. Now, regarding if you may heat it directly on the Blech or electric plate, this matter is under dispute. Likewise, regarding if you may toast it to the point that the bread turns hard like toast, this too is under dispute. Practically, my advice on the subject is to circumvent the issues and not place the bread directly on top of the electric plate but rather in top of an upside-down pot or baking pan. Likewise, one should not intentionally place the bread there for long enough time for it to become actual toast although if it happens to harden while one is trying to warm it up, it is fine.
Explanation: Some Poskim prohibit toasting bread on Shabbos due to that one is hardening a soft substance, which is prohibited under the cooking prohibition. Other Poskim rule that it is forbidden due to that it is considered like Afiyah after Bishul. Other opinions suggests that perhaps it would be forbidden due to Makeh Bepatish. Nonetheless, there are authorities who rule that it is permitted to be done and negate all of the above worries.
Sources: See Admur 318:7; Piskeiy Teshuvos 318:26 and 40 and footnote 377 See regarding making toast: Poskim who Prohibit: Shoel Umeishiv 2:20; Rav Poalim 2:52; Kaf Hachaim 318:78; Har Tzevi “Ofeh” p.262; Or Letziyon 2:30-6; SSH”K 1:62; Shabbos Kehalacha Vol. 1 p. 179; Maor Hashabbos 8 footnote 158; Piskeiy Teshuvos ibid and ibid; Poskim who Permit: Daas Torah 318:5; Shevisas Hashabbos Mivashel 92; Yagel Yaakov O.C. 54; Migdanos Eliyahu 3:37; See regarding placing directly on electric plate or blech: Shabbos Kehalacha Vol. 1 page 414-415; Piskeiy Teshuvos 253:27
May one heat an egg on Shabbos to the point it becomes hard boiled?
No. This may not be done even in a [Keli Shelishi].
May one heat an egg to less than Yad Soledes?
May one toast the sides of a Matzah on Shabbos for the sake of making it a Shaleim?
On Shabbos, or when Yom Tov falls on Shabbos, according to all it is forbidden to burn the sides of the Matzah for the sake of making it a Shaleim.
C. The forms of heating:
Cooking on fire heated objects: Similarly, just as it is forbidden to cook with fire so too it is forbidden to cook with an item that received its heat from fire. For example [it is forbidden] to place an egg near a pot that was heated from fire or to break [an egg] on a cloth that was heated from fire, in order [for the egg] to fry a little bit. If it was fried there to the point of the food of Ben Drusaiy he is liable for cooking just like if he had fried it [directly] on a fire. [However, cooking on sun heated objects is not Biblically forbidden as will be explained next.]
Cooking foods that are already partially cooked: Any [food] which has not yet been fully cooked, even if it was already cooked to the point of the food of Ben Drusaiy, [nevertheless] it retains the cooking prohibition even if it is currently boiling.
A food that is fully cooked but further cooking is beneficial: If the food is fully cooked then it does not contain a cooking prohibition [even Rabbinically] even if further cooking will still make it condense in a way beneficial to the food.
Cooking fruits and the like of foods which are eaten raw: Fruits or other foods which are eaten raw and thus do not need to be cooked, nevertheless if one cooks them, he is liable. Therefore, it is forbidden to place these [fruits] by an area where they can get cooked if left there for a long time, which is defined as any place where it can reach Yad Soledes.
Hastening cooking through stirring: [Furthermore it is forbidden] to hasten the cooking of a non-fully cooked food, such as by stirring it with a spoon, even if it will regardless cook on its own.
Do chicken bones need to be fully cooked to be allowed to further heat the chicken or the dish that they are in?
If one, or the majority of one’s city, is accustomed to eat the chicken bones, then the chicken bones must be cooked to the point that they are chewable. If neither oneself or the majority of one’s city eats them, they do not need to be cooked. If one is in doubt as to whether they have been cooked to the point that they are chewable, then if he himself does not chew them, even if majority of the city does, he is not required to be stringent.
Meat bones: Do not contain a prohibition of Bishul if they are cooked but not yet soft.
If one cooks food which receives damage from, is there a Biblical prohibition involved?
Wine: It is Biblically forbidden to cook wine.
Oil: It is Biblically forbidden to cook oil.
How long must the food cook, for one to transgress the Biblical prohibition?
There are numerous instances that Admur writes the amount of cooking that makes one liable for the prohibition. The following are some of those instances:
- It is forbidden to place cold [liquid] on top of a kettle ….. for a long time that it would be able to cook, which means that it would become Yad Soledes.
- A liquid dish…., if one heats it on Shabbos until it reaches [the heat of] Yad Soledes, he is liable for cooking.
- Any food which has not been [fully] cooked before Shabbos [whether liquid or solid], one may not soak it on Shabbos in hot [liquidly] food that is Yad Soledes even if it will not dissolve in there at all. If one [transgressed and] soaked it in a Keli Rishon he is liable for cooking.
- Therefore, it is forbidden to place these [raw fruits] by an area where they can get cooked if left there for a long time, which is defined as any place where it can reach Yad Soledes.
- Similarly, just as it is forbidden to cook with fire so too it is forbidden to cook with an item that received its heat from fire. [Thus] if it was fried there to the point of the food of Ben Drusaiy then he is liable for cooking just like if he had fried it [directly] on a fire. 
Summary- The following forms of cooking are Biblically forbidden:
1. Cooking, baking, roasting, frying any uncooked food over or near a fire, or over an item heated by a fire, to the point that it heats to Yad Soledes is a transgression of the Biblical cooking prohibition. Furthermore, even if the food was already cooked to Ben Drusaiy but was not fully cooked and one placed it on a fire or on an item heated by a fire in order to continue cooking it, or even if it was already on the fire and one stirred it to hasten its cooking, then one has transgressed the Biblical cooking prohibition. The prohibition includes even cooking a food that is commonly eaten raw, such as fruits and the like.
2. Melting/Softening an object such as metal, wax, fat, tar and sulfur by a fire [or by an item heated by a fire].
3. Hardening an object such as earthenware by a fire [or by an item heated by a fire]. [See Q&A]
 Admur 318:7
 Shabbos 74b; Tur and Beis Yosef 318
 Admur ibid; M”B 318:1
 Admur ibid; M”A 318:10; M”B 318:1
 Maggid Mishneh brought in Magen Avraham 318:36-37; Sheivet Haleivi 8:57; Shabbos Kehalacha Vol. 1 p. 27
 Meaning that although in general we rule that whenever something inevitably occurs it remains Biblically forbidden, nevertheless here all agree that intent is needed to make it a Biblical Melacha, and thus without intent it remains a Rabbinical prohibition, and is allowed when the inevitable act is not wanted. ]Maggid Mishneh brought in Magen Avraham ibid] Vetzaruch Iyun from Admur 318:21 based on M”A [brought in 9D] which rules we do say Pesik Reishei by Tikkun Keli. However, one can answer based on 646:13-14 that only when one has benefit do we say Pesik Reishei by Tikkun Keli, If however one does not have benefit then we do not say it, as he has no intent to make a Tikkun at all. [See Volo. 2 Bone Chapter 1 Halacha 1]
 Sheivet Haleivi 8:57; Shabbos Kehalacha Vol. 1 p. 27
 As a) one has no intent to weld the plastic and b) being that one has no intent to weld it, softening it is not even defined as a Melacha, and in such a case even an inevitable occurrence [Pesik Reishei] is permitted, as explained in previous question. [Sheivet Haleivi Ibid]
 Shabbos Kehalacha Vol. 1 p. 27 based on Peri Megadim 318 A”A 37; Shevisas Shabbos Mivashel 31; SSH”K 1 footnote 7
 Meaning that if the item melted due to Yad Soledes heat, one is liable even if the item itself did not become Yad Soledes. [Peri Megadim ibid] If however also the heat was less than Yad Soledes one is not liable. [Rav SZ”A ibid]
 Shabbos Kehalacha Vol. 1 p. 28-31
 Shoel Umeishiv Telisa 2:20; Rav SZ”A in SSH”K 1 footnote 148 regarding eggs and 173 regarding butter
 Sheol Umeishiv ibid
 Daas Torah 318:5; Rav Poalim 2:52
 Shabbos Kehalacha ibid based on Rav Poalim ibid; Tehila Ledavid 318:33
 Rav SZ”A regarding butter
 Shabbos Kehalacha ibid based on Rav SZ”a in SSH”K 1 footnote 173
 Shoel Umeishiv Telisa 2:20
 Shabbos Kehalacha Vol. 1 p. 63 based on Rav SZ”A in SSH”K 1 footnote 148
 Shoel Umeishiv 2:20; Kaf Hachaim 318:78; Har Tzevi “Ofeh” p.262; SSH”K 1:62; Shabbos Kehalacha Vol. 1 p. 179
The reason: Shut Shoel Umeishiv 2:20 forbids it due to that one is hardening a soft substance; Kaf Hachaim [318:78] rules it is forbidden based on that he considers this like Afiyah after Bishul. Shabbos Kehalacha Vol. 1 p. 179 rules like these opinions that toasting bread is forbidden. Har Tzevi “Ofeh” p.262 suggests that perhaps it would be forbidden due to Makeh Bepatish, although he rejects the logic of saying that one is hardening a soft item.
 Daas Torah 318:5
 Shabbos Kehalacha Vol. 1 p. 188
 See Shabbos Kehalacha 1 p. 28
 Piskeiy Teshuvos 274:10 due to the cooking prohibition of hardening a soft item; See Admur 318:7; Shoel Umeishiv 2:20; Kaf Hachaim 318:78; Har Tzevi “Ofeh” p.262; SSH”K 1:62; Shabbos Kehalacha Vol. 1 p. 179; Daas Torah 318:5
 Admur 318:7; Michaber 318:3; Shabbos 38
 Admur 318:10; 253:18; Rama 253:2; Michaber 318:4 and 18; M”B 253 Biur Halacha “Vedavka Shehatvshil”; See Piskeiy Teshuvos 253:18
Other Opinions: Some Rishonim rule that further cooking of a food that has reached Ben Drusaiy is permitted on Shabbos. [See Biur Halacha ibid and 318:4; Even Yisrael 8:28; Piskeiy Teshuvos 253:18]
 Admur 253:18; Biur Halcha 253:2 “Mutar Lehachziro”
 Admur 318:24; 254:4; Rama 318:14; Olas Shabbos 318:40; Birkei Yosef 318:3; Or Zarua 62; P”M 218 M”Z 6; M”B 318:91 and Shaar Haatizyon 318:114; Kaf Hachaim 318:60
Other Opinions: Some Poskim rule one does not transgress a Biblical prohibition by cooking raw fruits that are edible and rather it is merely Rabbinically forbidden. The reason for this is because they hold that the fruits are considered no less than a Ben Drusaiy food and according to them a food that is cooked to Ben Drusaiy does not contain Biblical prohibition in further cooking. [Ridbaz 1:318; See Birkeiy Yosef ibid] However based on the ruling of Shulchan Aruch that we do hold that cooking a food that is already Ben Drusaiy involves a Biblical prohibition, therefore here too the cooking of a raw fruit would be Biblically forbidden. [Kaf Hachaim 318:60]
 The reason: As the fruits are enhanced through the cooking and hence retain a prohibition of Bishul. [Shaar Hatziyon 318:114]
 Admur 318:10
 Rav SZ”A in Minchas Shlomo 6; Shabbos Kehalacha Vol. 1 p. 200; See SSH”K 1:18; Piskeiy Teshuvos 253:18; See Minchas Yitzchak 8:25
Other Opinions: Some Poskim rule there is no cooking prohibition involved in bones. [Igros Moshe 4:76]
 Minchas Shlomo ibid
 Or Zarua 62; Kaf Hachaim 318:60; See M”B 318:91 and Shaar Hatziyon 318:114
 In 318:7 Admur implies one is only liable if one heats the food to Ben Drusaiy. In 318:9;11;24;29 Admur implies that one is liable even if cooked to Yad Soledes. Vetzaruch Iyun. Perhaps however one can explain that for food [solids] the liability for a Chatas offering only applies if one cooked a food to Ben Drusaiy while the Biblical prohibition applies once it is heated to Yad Soledes, as at that point it begins to cook. However, for liquids the liability for a Chatas offering is when it is Yad Soledes. This can also be seen within the wording of the different cases mentioned, that Admur never states by solids that there is liability when heated to Yad Soledes and rather only mentions that it is forbidden. Perhaps the reason behind the differentiation between food and liquid is because the liability is with regards to cooking the food to the point that it is considered cooked enough to eat, as only then has the food truly benefited from the cooking. Hence by solids this amount is Ben Drusaiy, while by liquids it is Yad Soledes.
 Admur 318:29
 Admur 318:9
 Admur 318:11
 Admur 318:24
 Admur 318:7
 In 318:7 Admur implies one is only liable if one heats the food to Ben Drusaiy. In 318:9; 11; 24; 29 Admur implies that one is liable even if cooked to Yad Soledes. Vetzaruch Iyun. Perhaps however one can explain that for food [solids] the liability for a Chatas offering only applies if one cooked a food to Ben Drusaiy while the Biblical prohibition applies once it is heated to Yad Soledes, as at that point it begins to cook. However, for liquids the liability for a Chatas offering is when it is Yad Soledes. This can also be seen within the wording of the different cases mentioned, that Admur never states by solids that there is liability when heated to Yad Soledes and rather only mentions that it is forbidden. Perhaps the reason behind the differentiation between food and liquid is because the liability is with regards to cooking the food to the point that it is considered cooked enough to eat, as only then has the food truly benefited from the cooking. Hence by solids this amount is Ben Drusaiy, while by liquids it is Yad Soledes.
 Admur 318:10
 Admur 318:24
 Admur 318:7