The following is the policy of the OU regarding temperature levels:
Minimum required to maintain bishul or pas yisroel: 176°F
Applications:
- A Jew modified the flame in an oven to avert a problem of bishul akum or pas paltar and that flame was subsequently extinguished and relit by a non-Jew. The food cooked in the oven after the fire was relit is only bishul or pas yisroel if the oven chamber was at least 176°F during the entire time the flame was off.
- A Jew modified the flame in a boiler to avert a problem of bishul akum or pas paltar and, some time later, the company turned off the boiler for 8 hours in order to service it. If the boiler maintained a minimum temperature of 176°F during the hours that it was off, a non-Jew may relight the boiler and the food will still be considered bishul or pas yisroel.
Hagalah and pegima: 212°F
Applications:
- Equipment which requires hag’alah must be kashered in water which is at least 212°F even if the non-kosher food cooked in the equipment never reached that temperature.
- Non-kosher oil was heated to 350°F in a deep fryer. The deep fryer can be kashered with water which is 212°F even though the oil was hotter than that.
- The temperature of the water must be 212°F and it is irrelevant if the water is boiling or not. Therefore:
- Hag’alah can be done with water which is 212°F even if the water isn’t “boiling” because it is under pressure.
- Hag’alah cannot be done with water which is less than 212°F even if the water is “boiling” because it is in a vacuum.
- Hag’alah cannot be done with liquids (e.g. alcohol) which are less than 212°F but are “boiling” because their boiling point is less than that of water.
- All of the aforementioned rules also apply to one who is being pogem equipment in anticipation of kashering it before it is aino ben yomo.
- There are limited situations where hag’alah and pegimah may be done at lower temperatures but only after the situation is evaluated by a kashering expert.
Minimum baking temperature which demands libun gamur: 200°F
Applications:
- A dryer which processes non-kosher breakfast cereal at less than 200°F may be kashered with libun kal (or hag’alah) even though the cereal is dry and the flame is very close to the drying chamber.
- There are limited cases where libun gamur is not necessary even if the temperature is somewhat higher than 200°.
Libun gamur for a thin item or if applied for an extended amount of time 900°F
Applications:
- A belt which comes in direct contact with non-kosher pastries in the oven can be kashered by heating the belt to 900°F for a few seconds (using the procedure outlined in K-285 to prevent it from buckling).
- A baking pan or frying pan which was used to bake or fry a non-kosher item can be kashered by allowing them to go through an oven’s entire self-clean cycle since the pans will be heated to 900°F for many hours.
- A pizza oven was used to bake non-kosher food which came in direct contact with the floor of the oven. Momentarily heating the oven to 900°F is insufficient to kasher it.
Libun kal performed without a direct flame
—Temperature of the equipment itself as opposed to the air in the equipment 1 hour at
550°F or
1½ hours at 450°F or
2 hours at 375°F
Applications:
- Non-kosher bread was baked in an oven on pans. After the oven is cleaned, the chamber (as opposed to the pans) can be kashered by heating it until the walls, floor and ceiling of the oven reach 550°F and then this temperature must be maintained for one hour. Alternatively, the walls etc. can be heated to 450°F for 1½ hours or to 375°F for 2 hours.
- A spray dryer can be kashered by heating its walls to 550°F and maintaining that temperature for 1 hour, to 450°F and maintaining that temperature for 1½ hours or to 375°F and maintaining that temperature for 2 hours. Special care must be taken to insure that even the coldest portions of the spray dryer reach the required temperature.
- In many of the above cases, the equipment’s temperature measuring device will measure the temperature of the air in the chamber. This temperature should be ignored because libun kal requires that the equipment reach the required temperature.
- Mishnah Berurah 451:33 notes that libun kal can remove residual issur left in the cracks and crevices of a utensil. That libun kal requires a direct flame as described below; libun kal without a flame at the temperature described above would not effective.
Libun kal performed with a direct flame: 160°F on the backside of the equipment
Applications:
- A stainless steel worktable/counter was used for hot non-kosher meat. The counter can be kashered by slowly passing a blowtorch over every inch of the top of the counter until the entire underside of the counter reaches 160°F (i.e. yad soledes bo).
- The same procedure can be followed for a drum dryer heated by steam (as opposed to one heated by a flame or electric element which would require libun gamur).
Yad soledes bo – minimum: 120°F
Sources—K-185 & X-1:17
Applications:
- Non-kosher patties come out of the oven and get transferred onto a series of belts. Those belts which come in contact with patties which are hotter than 120°F must be kashered before they are used for kosher products. Those belts which come in contact with patties which are cooler than 120°F do not have to be kashered.
- A heat exchanger is used to keep warm non-kosher products from getting too hot. If the products never get hotter than 120°F and all remnants of the non-kosher product have been removed, the heat exchanger can be used for kosher products without hag’alah.
- A non-Jew curdles cheese in a temperature-controlled vat and produced whey as a byproduct. If the vats get hotter than 120°F, the whey is forbidden because it has absorbed taste from the gevinas akum. Otherwise, the whey is kosher.
- On Shabbos, one may place a cold liquid next to the fire if it is impossible for the liquid to become heated to above 120°F.
- There are limited cases where one may consider yad soledes bo to be 125°F .
Yad soledes bo – maximum: 165°F
Applications:
- Cold stam yayin, milk, or chametz was kovush in a tank for 24 hours. The tank can be kashered via irui kli rishon using water which is at least 165°F.
- Liquids which were heated to 165°F are considered fully cooked as relates to bishul on Shabbos.
For wine or grape juice to be considered mevushal: 175°F
Applications:
- Wine or grape cannot become forbidden as stam yayin after it was pasteurized to 175°F.