Examples of Bishul: Cooking, baking, melting metal, melting wax or tar, hardening clay vessels in a kiln, drying sticks on an oven. The general rule is softening or hardening with fire is Bishul. (MB 1)
Chatzi shiur ossur min haTorah. Therefore, even if the cooking is done to an amount of food less than a dried-fig-size and less than a third cooked, it is still ossur d’oraisa. (MB 1)
If someone transgressed by mistake (b’shogeg) and cooked on Shabbos, no-one is allowed to eat the food until (immediately) after Shabbos. Some poskim hold that there is no penalty at all on the food when he doesn't know the halacha – you can rely on this if need be. (ShA 1 – MB 7)
This penalty applies only when a d’oraisa was transgressed according to all poskim, but if it was only d’rabbonon or some poskim hold it isn't Bishul, there is no penalty. (MB 2, 3)
Cooking by means of toleddes ha’ur (an object heated by fire) is chayav. It is Bishul just as with direct fire. (ShA 3 – MB 17)
Cooking in the sun is permitted. However, Chazal decreed not to cook by means of toleddes chama (an object heated by the sun) lest people confuse it with toleddes ha’ur. Therefore, do not roll a raw egg on the hot sand to roast it on Shabbos. (ShA 3)
Cooking in hot springs is ossur mid’rabbonon on Shabbos. (MB 20) .
A leniency: “Ain Bishul achar Bishul”. Therefore you are allowed to steep a fully cooked solid food in very hot liquid on Shabbos. This rule has many exceptions therefore the following would have the issur of Bishul:
The cooked food is liquid and completely cooled down – it becomes “uncooked” once again. (This is disputed.) (ShA 4 – MB 24, 29 – BeH “yesh”)
The food is not fully cooked. (Some dispute this if the food is already k’maachal ben d’rusai.) (ShA 4 – MB 27)
The hot cooked food has been poured into a kli shayni. (BeH “im”)
The food was cooked only in a kli rishon off the fire. (Some dispute this if it is a food-type that gets fully cooked in a kli rishon. ) (MB 31)
The cooked food goes back onto the fire for the first time on Shabbos. (This is ossur anyways because of Chazara. See above Siman 253.) (ShaH 46)
The food was originally baked or roasted (dry heat). “Yesh Bishul achar Afia.” “Yesh Bishul achar Tzli”. This applies the opposite way as well: don’t put boiled food next to the fire or other heat source in a place that could become yad soleddes. “Yesh Tzli achar Bishul”. Accordingly – it is ossur to put bread into hot soup even in a kli shayni. (This is disputed. Some poskim hold there is no Bishul after any method of cooking with fire.) (ShA5 – MB41)
If you take a pot off the stove on Shabbos and you don't know if it is fully cooked- don’t return it to the stove (even with a blech). (BeH “shayach”)
What is permitted in a kli shayni?
You may mix a cooked liquid that has completely cooled down into a hot liquid in a kli shayni. (MB 23)
Solids that were cooked by merely steeping in kli rishon (off the fire) may be heated in hot liquid in a kli shayni. (MB 31)
Do not put raw foods into hot (yad soleddes) water in a kli shayni.. (See below spices are muttar) (ShA 4 – MB 34)
Pouring hot water from a kli rishon has the ability to cook the surface of raw food. Pouring hot water from a kli shayni has the ability to cook raw salted fish and any raw, very thin and soft food. (e.g. tea leaves) (ShA 4 – MB 35, 39 – BeH “kolyas”)
Pouring cold water over food (or steeping in cold water) to make it edible is allowed. (MB 37)
The following are muttar ways of making tea on Shabbos in an ascending order of preference:
Before Shabbos pour hot water from a kli rishon (kettle) over all sides of the tea leaves – let them dry – on Shabbos, pour hot water from the kettle directly onto the pre-cooked tea leaves. Beware not to put the tea leaves onto the blech (a place that can become yad soleddes).
Before Shabbos, cook the tea leaves properly on the stove – so they are cooked through and through. Continue with the above.
Prepare the tea essence before Shabbos. On Shabbos, **first** pour from the kettle into a kli shayni – then pour the cold essence into the hot water. Cooled milk can also be added. There is no problem in coloring the water.
Prepare tea essence and keep it from cooling down – **first** pour the essence into the kli shayni – then the hot water. You will be fulfilling the opinion that holds against dying the hot water. (MB 39 – ShaH 64, 65)
Just as we hold Ain Bishul achar Bishul – so too, Ain Tzli achar Tzli and Ain Afia achar Afia. You therefore can reheat roasted meat or bread next to fire. (MB 41)
Do not put raw onion or bread into a bowl of soup until it cools to under yad soleddes. (MB 45)
If you do not want to wait for the soup to cool down, at least use a ladle (kli shayni) to dole out of the soup pot so the soup bowl will become a kli shlishi. The Pri Megadim says you can be maykil with a kli shlishi (even with tea).(MB 45, 47)
Some poskim hold that a hot solid (davar gush) has a din of kli rishon even when resting in a kli shayni. (MB 45)
You aren’t allowed to put fully cooked food directly on the blech because it looks like you are cooking. However, reheating the food (or cooked liquid that has not completely cooled) on top of a pot cooking on the stove, **is** allowed – that’s not the way people cook. (ShA 8 – MB 59)
A kli rishon removed from the fire can still cook if the contents are yad soleddes. Hot solids might still keep the status of kli rishon so don’t put spices on them. See above # 348 (ShA 9 – MB 65)
Most poskim say that raw salt does not cook in a kli rishon. Accordingly, you can salt your cholent while it’s still in the pot. Some poskim hold that raw salt **will cook even in a kli shayni** – if you follow their chumra you will get a beracha. (Rama 9 – MB 71)
Sea salt has been cooked already – you can add it to a kli rishon. (MB 71)
Sugar has been cooked already. Nevertheless, since there are poskim who forbid adding it to a kli rishon – it is good to avoid this. (MB 71)
If someone salted a pot of food with raw salt while the food was still on the fire it will be ossur to eat until Motzoay Shabbos. However, if some salt was already put in before Shabbos, and just a little bit more was added on Shabbos to make it tasty, the food is muttar. (MB 73)
As stated above (#342), pouring from a kli rishon will cook the surface of uncooked foods. So, if you direct an uninterrupted stream straight onto the food – you have cooked it and won't be allowed to eat the food. (ShA 10 – MB 74)
As stated above (#341), beware of steeping uncooked food in kli shayni water (except for spices, water and oil). However, if you did, the food won't be ossur to eat. (BeH “ossur”)
**Are you allowed to pour cold water into hot water?** No, if it is a small amount of cold into a kli rishon (or **very** hot water even into a kli shayni). If there is so much cold water that the pouring will result in warm water it is muttar. (ShA 11, 12 – MB 77)
**Are you allowed to pour hot water into cold water?** Yes. from a kli shayni. But if the hot water is being poured from a kli rishon onto a small volume of cold water there is a dispute. Therefore, for yourself be machmir – but do not protest against people who pour from the kettle directly onto cold tea essence. If the cold water is of larger quantity then the poured hot water – it is muttar in any case. (ShA 11, 12 – MB 78 – BeH “sheb’zeh”)
Just as you aren't allowed to pour a bit of cold water into a kli rishon of hot water – so too you aren't allowed to put a container of cold water into a kli rishon of hot water if it will become hot. (ShA 13 – BeH “aval”)
If you leave a ladle inside a soup pot until it boils – the ladle gets the status of kli rishon as well. (MB 87)
Do not put a cold fruit or container of water next to a fire, so close that it could become yad soleddees. This is so , even if you plan on just taking off the chill from the fruit for a minute – you might forget to take the fruit away from the fire. (ShA 14 – MB 90)
As stated above, you are allowed to reheat a solid next to the fire. What about congealed gravy? It will melt into a liquid, but there is no issur Bishul since it is deemed as a solid when going to heat it. However, there is an issur of Molid if the melted food will be recognizable separately from other food. (ShA 16 – MB 100, 105)
The following cases have no issur of Molid:
Putting ice into a warm drink. (MB 102)
Putting warm drinks into ice is a dispute. Be machmir l’chatchila. (ShaH 146)
The solid food will melt only slightly to soften. (MB 105)
A small amount of congealed gravy stuck to a piece of meat. (MB 105)
Put the congealed gravy near a heat source before it turns on. (MB 106)
There are opinions that prohibit Molid only when actively chopping the solid into liquid – but any method of getting the food to melt by itself is allowed. You may rely on this opinion if you need it for Shabbos. (Rama 16 – ShaH 133)
Stirring food in a hot kli rishon (even if removed from the fire) is Bishul. There is room to be machmir even when the food is fully cooked. (ShA 18 – MB 117)
When emptying the contents of a kli rishon you can pour it out into a kli shayni or remove it from the fire and then use a ladle to scoop it out. But if the food is not fully cooked, don’t ladle it out since it is like stirring and will cook the food further. (ShA 18 – MB 117)
Do not baste raw garlic and oil on hot skewers of food – the food is toleddes ha’ur and will cook the sauce. This applies while the skewers are on the grill, removed from the grill, and even when the hot skewers are put down onto a kli shayni. Bedieved, if you basted the skewer after it was put onto a kli shayni, the food may be eaten since we rely upon the poskim who hold food in a kli shayni does not cook in any case. (ShA 19 – MB 118)
Solidified fat has already been cooked, therefore, you are allowed to baste with it even next to the fire. Just beware of smearing on a lot at a time in which case you will be melting it by force – that's Molid. (MB 118)
You may put a big chunk of solidified fat (shmaltz) on a hot bowl of rice and allow it to melt by itself. (MB 118)