Kashering: Pots and Utensils: Libun: How It Works  
Kashering by “burning” (libun) burns up any residual food taste and is of two types:

• “Complete burning” (libun gamur), and
• “Light burning” (libun kal).

Libun Gamur: Heating To Red-Hot for Direct-Heat Utensils
Libun gamur (complete burning) is when the entire metal substance of a utensil, oven, or other cooking surface becomes red hot.
When To Use Libun Gamur
Heating to red-hot (libun gamur) is required to kasher utensils that are used with direct heat, such as baking pans, roasting pans, and roasting grates. Libun gamur works on anything except pottery (this is a rabbinic injunction since you might not do a good job).
How To Do Libun Gamur
Libun gamur can be done by blowtorch or by placing the item in a kiln.

Libun Kal: Heating so Other Side of Pot Singes Paper

Heating so that the heat goes through to the opposite side of whatever is being kashered is called libun kal. 
When To Use Libun Kal
This method may be used whenever there is a question of whether an item needs libun or not, such as grates on a gas stove.Grates on a gas stove are considered questionable since food may have overflowed onto them and, due to safek, we kasher using libun kal.
Note Grates on a gas stove do not need libun gamur.
Note Whenever hag'ala is effective, you may instead use libun kal, since libun kal is a stronger form of kashering. Sometimes you may find it more convenient to use libun kal to kasher an item that needs only hag'ala. You may use libun kal instead of hag'ala since libun kal is a stronger form of kashering.
Situation A stainless steel pot of the opposite gender went through a dishwasher cleaning.
What to Do Even though the pot only needs hag'ala, you may instead kasher it by libun kal by putting it in an oven at 500° F (for this application).
How To Do Libun Kal
Direct a flame, such as a blowtorch, onto the inside of a pot. Pot is hot enough when a piece of paper that touches the outside of the utensil burns (it need not burst into flame, just to smolder and be consumed).

You may not do any action that may cause religious Jews to do something wrong or cause people to think that an observant Jew is doing something forbidden (mar'it ayin). Mar'it ayin is doing something that might lead people to:

• Violate a Torah law by thinking that an observed action that is permissible under special circumstances may be applied to other cases, or
• Think that the person doing the action is violating Torah law (since the observer might not know that the action is actually permissible).

If no one can see you, you may do activities that might look like violations of rabbinic laws. If the action is forbidden by the Torah (d'oraita), you may not even do it in private (but you may not actually violate either type of law!).

Property may be given away in any manner and amounts desired during a person's lifetime. A Jew must give his property away before death if he does not want to make the inheritance according to Jewish law (such as double portion to a father's first-born son, etc.--consult a rabbi for details). A person should reserve some money to fulfill the Torah commandment of inheritance. Consult a rabbi.
Since a person cannot give away property after his/her death (since he/she does not own it anymore), an American will has no halachic validity. An American will should be written to keep the inheritance out of the hands of the government and lawyers. In order for a secular will to be effective under halacha, an acquisition should be made that starts to take effect beginning at the time of the kinyan and finalize one hour before the person's death. 
Rabbinic guidance is recommended.

The Torah forbids cooking on Shabbat.   “Cooking” means making food edible by heating it to above 120° F (49° C).
Cooking includes:

• You may not make a soft food hard (such as cooking an egg).
• You may not make a hard food soft (such as cooking meat).
• You may not, in any manner, heat (to 120° F or above ) liquids that you will drink or foods with liquids—such as sauces and gravies--whether fully cooked or not. 

According to the Torah, you may eat food on Shabbat that had been placed on the heat source Friday afternoon but was not completely cooked by sunset.
ReasonNo action is being taken and the cooking will be completed by itself.
 
According to Torah law, food is only considered to be cooked if it has been directly heated from the heat source, such as a kettle on a fire or a pot on a flame (even if that utensil has been removed from its heat source). This is called a kli rishon.
Once you pour water from a kli rishon into a glass, the glass is a kli sheni. Some foods, such as an egg or tea, get cooked in a kli sheni (kalei bishul--easily cooked). These foods are forbidden by Torah law to be put into a hot kli sheni on Shabbat.

• You must have taken it off with the intention of replacing it, and
• You may not put the utensil down onto a surface; you must continue to hold the food (or the utensil) in your hand.
• The heat source must be covered.

Gender/Kashrut Status Transfer
Foods and kitchenware (pots, pans, dishes, utensils, and containers) can absorb taste from each other and so adopt a new gender or kosher status. They can change from:

• Kosher to non-kosher,
• Kosher pareve (neutral) to kosher dairy or kosher meat, or
• Kosher Passover to kosher (or non-kosher) non-Passover.

 
Note You can sometimes change a utensil/container to kosher-pareve (see Kashering, below), but you cannot change a

• Gendered food to neutral-pareve, or
• Non-kosher food to kosher.

 
Taste Absorption
Taste gets absorbed in three ways: Heat, pressure, and soaking. 
 
Heat
To absorb taste, and therefore gender or kashrut status, through heat, a food or utensil must be heated to 120° F or more while:

• Steamed with a halachically “liquid” food, or
• In wet physical contact with the food or utensil.

Examples

• Two hot pans, which are clean on their outsides, only transfer taste from one to the other if they are wet on the outside and are touching each other.
• A hot utensil placed onto a counter only transfers gender to the countertop if there is liquid or food at the point of contact.

Note  All liquids plays a major role in facilitating taste transfer.
NOTE Taste, gender, or non-kosher status do not travel upstream into the utensil that food is being poured from. Even if you pour hot liquid (pareve or of one gender) from a pot onto a non-kosher or opposite gender food, the genders are not transferred back through the stream of liquid to the pot, even if any or all of the elements are more than 120 degrees.
Situation You pour hot liquid from some pareve vegetables into a non-kosher sink that had hot in it within 24 hours. There are dishes or utensils in the sink.
Status The dishes do not change gender unless the hot liquid fills up from the sink onto them. If so, the dishes or utensils become non-kosher. But no gender change occurs through the stream of liquid back to the pot of vegetables.
 
Note If the non-kosher sink had not had anything hot (120 degrees or above) in it for at least 24 hours, no change of gender or kosher status happens at all.
 
Note On Passover, gender and chametz status DO get transferred through a stream of hot liquid.
 
Pressure
To absorb taste, and therefore gender or kashrut status, through pressure or short-term soaking, one of the items must be spicy/charif.
 
Soaking
To absorb taste, and therefore gender or kashrut status, through long-term soaking, the food must soak for specific amounts of time.
 
Note If the food or utensil is not hot (120° F or more), is not spicy/charif, and is not soaking for a long time, there is no gender or kashrut-status transfer.
Examples
You may use a non-kosher utensil for any cold food of the opposite gender, so you may:

• Eat cold (kosher) cereal out of a meat or non-kosher bowl, or
• Use a meat or non-kosher spoon to eat kosher ice cream.

Note Even though these are permissible, they may not be done regularly but only on an ad hoc basis.
 
Food and Kitchenware: Which Influences What
Hot or Spicy/Charif Foods
With hot (more than 120° F) or spicy/charif foods:
Foods and utensils/containers transfer taste to each other.
 
Cold or Non-Spicy Foods that Soak
With cold (less than 120° F) or non-spicy/charif foods that soak:

• Foods do not transfer taste to utensils/containers;
• Utensils/containers do NOT transfer taste to foods.

NOTE No substances (not salt, or any food...) absorb gender from the open air.
 
 
The 24-Hour Rule: Eino ben Yomo
Torah Law: Reverts to Kosher-Pareve
By Torah law, a utensil/container always reverts to kosher-pareve after 24 hours (since the taste of any absorbed food becomes ruined with time). 
 
Rabbinic Law: Must Be Kashered
However, by rabbinic law, the utensil/container must be kashered before using.
 
NOTE Even by Torah law, a hot or spicy/charif food can revive the milk-meat or non-kosher status of another utensil/container (see below) even after 24 hours.
 
Accidentally or Intentionally
Food Hot and Accidentally Placed; Utensil Not Hot for 24 Hours
Kosher food hotter than 120° F (49° C) remains kosher if accidentally placed into a non-kosher, clean utensil that has not been heated to 120° F or more for at least 24 hours.
REASON After 24 hours, b'di'avad, the utensil has reverted to being kosher-pareve.
NOTE If the utensil had been “used” (heated to 120° F or more) within the preceding 24 hours, the hot food that accidentally entered the utensil would be non-kosher. Ask a rabbi for possible exceptions.
 
Food Hot and Intentionally Placed
If the hot food had been put into the utensil intentionally, the food would not be kosher.
REASON Chazal made a rule (takana) that if you intentionally place food of one gender into a utensil of the opposite gender and heat it to 120° F or more, the food is not kosher.

Cheese/Gvinas Akum
 
Gvinas akum is cheese which has been made by non-Jews and by rabbinical prohibition is only kosher if a Jew was present during the cheese making OR if a Jew put the rennet into the milk.
Note If a Jew owns the milk before processing, a non-Jew can add kosher rennet as long as it can be confirmed that the rennet is kosher, even if no Jew is present during the cheese making.
 
Origin of the Problem: Chazal were concerned that the rennet used to make cheese might be from a non-kosher animal or even from a kosher animal that had not been slaughtered properly. Shulchan aruch says that even cheese curdled by kosher plant enzymes (such as fig branch sap or substances from certain thistle plants) are subject to the takana.
Note Gvinas Akum is not related to chalav yisrael; they are separate halachot.

Note Even rennet-less cheeses need hashgacha (religious supervision), but some non-hard cheeses may be an exception. Ask a rabbi.

We are required to eat two meals on Jewish festivals, each preceded by kiddush, one in the evening and one in the morning. For both meals for each Jewish festival day (and all three meals on Shabbat), say ha'motzi over two complete loaves of bread, each of which is at least 1.3 fl. oz. in volume. 

Source of Saying Jewish Festival Kiddush
Some kiddushes are commanded by the Torah (d'oraita); the others are from Chazal (d'rabanan), as follows:
Kiddush d'Oraita

• First night of Jewish festivals
• Night of seventh day of Passover
• Night of Shmini Atzeret.

Kiddush d'Rabanan

• First day of Jewish festival
• Second night of Jewish festival
• Second day of Jewish festival
• Seventh day of Passover
• Eighth night of Passover
• Eighth day of Passover
• Shmini Atzeret day
• Night and day of Simchat Torah.

Source of Jewish Festival Kiddush Location
Saying Jewish festival kiddush at the place where you will eat your meal is a rabbinical (d'rabanan) enactment.
Jewish Festival Kiddush-Meal Quantities: Evening

• For evening kiddush for a first-night (d'oraita) Jewish festival, a minimum of 4 fl. oz. (119 ml) of wine must be blessed on and at least half must be drunk.
• For evening kiddush for a second-night (d'rabanan) Jewish festival, a minimum of 3.3 fl. oz. (99 ml) of wine must be blessed on and at least 2.0 fl. oz. must be drunk.
• For the evening meal, as on the first two Shabbat meals and for all required Jewish festival meals, a minimum of 1.9 fl. oz. (56 ml) of bread must be eaten within four minutes.

Eating Requirements for Jewish Festival Morning Kiddush
There are two separate eating requirements during the daytime. They may be combined (say/hear kiddush and start the main meal right away) but are often done separately (say/hear kiddush and then eat some light foods and beverages; the main meal is eaten later in the day).
Note Since eating and drinking requirements on all morning kiddushes (both Shabbat and Jewish festivals) are d'rabanan, the required beverage amount for morning kiddush is only 3.3 fl. oz. (99 ml) instead of the d'oraita 4 fl. oz. (119 ml) (which is required for kiddushes for Shabbat evening and all first-night Jewish festivals).

• Morning kiddush requires a halachically legal “meal” with these elements:
  • Blessing on a minimum of 3.3 fl. oz. (99 ml) of wine (or other beverage),
  • Someone's drinking at least half the beverage, followed by
  • Eating at least 1.3 fl. oz. (39 ml, or 1/6 cup) of some type of mezonot within four minutes. 
    Note If you drink at least 3.3 fl. oz. (99 ml) of wine within 30 seconds, you do not need to eat mezonot.
    Note You do not need to drink the wine or other kiddush beverage to fulfill “establishing a meal.” You may hear kiddush and then simply eat the required amount of bread or mezonot. This applies to Shabbat or Jewish festivals, evening or morning.
     

 

• The real meal (kovei'a se'uda) requires eating at least 1.9 fl. oz. (56 ml) of bread (or matza during Passover!) within four minutes. It must include enough food to satiate. 
  Note You can simultaneously fulfill the requirement to “establish a meal” and to “eat a meal” by eating one (the same) piece of bread.

Categories of Batel/Nullification
Categories of nullification of non-kosher ingredients:

• Never batel.
• Batel b'shishim when the non-kosher substance is less than 1/60th of the total volume of the food.
• Batel barov when the non-kosher substance is less than 1/2 of the total volume of the food.

When Can a Non-Kosher Substance Be Nullified in a Mixture?
Whether a non-kosher substance can be nullified in a mixture depends on 3 factors:

• Whether the owner is Jewish;
• Whether the intended eaters are Jewish; and
• Whether the non-kosher substance was added intentionally as non-kosher.

If the answers to all three cases is yes, the food is never batel.

Food “Nullified in 60 Parts”:
Accidentally Adding Non-Kosher to Kosher Food 

• Less than 1/60 of the volume of the whole.
• Mixed in and not lying on the surface.
• Not intentionally added by a Jew.
• Not listed in “Foods that Never Become Nullified” (below).

Min b'Mino
Substances are only batel when they are similar (“min b'mino”). The substances must be the same type, have the same taste, and have the same appearance (the eater cannot identify them as being different).
Note In such situations, it would be batel barov from Torah (d'oraita) but batel b'shishim (1/60^th) by rabbinical order (d'rabanan).
Example A piece of non-kosher meat is mixed in with kosher meat of more than 60 times the volume of the non-kosher piece. The non-kosher meat is batel b'shishim.
Note As a practical matter, this can only apply to ground meat.
Counter Example Non-kosher chocolate syrup or a non-kosher flavored extract mixed into milk or other liquid or onto a solid would NOT be min b'mino even though both are liquids, since their appearances, flavors, and substance are different.

Too Thin To Make Non-Kosher

• Yayin Nesech
  Wine that has been offered to a pagan god or used for idolatrous purposes (yayin nesech) is forbidden in any amount!
• Mixtures of Milk and Meat
  Mixtures of milk and meat are not ever batel if they were cooked together.
  ExceptionBatel in 1/60^th if:
  • You cannot identify either substance AND
  • The mixture is liquid in liquid or solid mixed with solid.

Examples: Milk from a pig mixed with milk from a cow; ground kosher meat mixed in with ground non-kosher meat.

• Chametz

• Jew Intentionally Adding Non-Kosher Item

• Unflavored or Flavored Non-Kosher Ingredient
  
  Non-Jew Adds Unflavored Non-Kosher Ingredient
  

  Situation A non-Jew adds a non-kosher ingredient that has no flavor. 
  Status The non-kosher ingredient is nullified if less than 1/2 of the total (it does not need to be less than 1/60th--batel ba'shishim).

  
  Non-Jew Adds Flavored Non-Kosher Ingredient

  Situation A non-Jew adds a flavored non-kosher ingredient even if to impart flavor.
  Status The non-kosher ingredient is nullified in 60 parts (batel ba'shishim).
  

  Note If a Jew had told the non-Jew to add the ingredient, the mixture is non-kosher, just as if a Jew had added it. 
• Stam Yeinam Added to Water
  Situation A non-Jew adds—to water--stam yeinam (uncooked/non-mevushal) wine that has been handled while open by anyone other than a shomer-Shabbat Jew.  
  Status As long as the wine is less than 1/7th of the final volume, the mixture is kosher. 

  Note For mixtures with liquids other than water, consult a rabbi. 

• Essential Additives

• Food Bought by the Piece

• Important Food

• Permissible in Future (Davar SheYesh Lo Matirin)

• An egg laid on Shabbat will not be nullified by being mixed with eggs laid before Shabbat.
• Matza made of chadash flour will not be nullified by being mixed with matza made from yashan flour.

• Whole Insects

• Frozen or raw chopped or ground vegetables or spices may be considered kosher even without supervision.
  Reason We assume that any bugs in the food would have gotten partly chopped or disintegrated and therefore nullified.
• If a recipe calls for chopping or grinding herbs or vegetables, you may do so without first checking them for bugs.
  Note However, if you know there are bugs, you may not chop the food for the purpose of making the bugs nullified:  You must still check for insects before cooking or eating the food and if you see any bugs, you must remove them.

Jewish Festivals are listed in the Torah and are of two types: 

1. Three pilgrimage festivals (shalosh regalim):

• Passover,
• Shavuot, and
• Sukkot (including Shimini Atzeret).

These festivals were celebrated in ancient times by "appearing before God"--by bringing offerings to the Tabernacle or Temple.

2. High Holidays: 

• The Jewish New Year (Rosh Hashana—“Yom Teru'a” in the Torah), and the
• Day of Atonement (Yom Kippur).

 
Duration
Jewish holidays that were originally one day are now observed as follows:

• Rosh Hashana--2 days.
• Yom Kippur--1 day.
• Shavuot--1 day in Eretz Yisrael or 2 days elsewhere.
• Passover has festival days at the beginning and end of the holiday and intermediary days of lesser holiness, which are called chol ha'moed. In Eretz Yisrael, Passover lasts for 7 days in total and the first and last days are festival days. Outside of Eretz Yisrael, Passover lasts 8 days and has two festival days at the beginning and two at the end.
• Sukkot has festival days at the beginning and at the end and intermediary days of lesser holiness, which are called chol ha'moed. In Eretz Yisrael, Sukkot lasts for 8 days and the first and last days are festival days (the last day is Shimini Atzeret). Outside of Eretz Yisrael, Sukkot lasts for 9 days and the first two days and last days are festival days (the 8th day is Shimini Atzeret and the 9th day is Simchat Torah).

Character
Each holiday contributes its own character to Jewish life (Passover--the theme of freedom; Yom Kippur brings atonement, etc.). 

Celebrating
How to celebrate these holidays is detailed in our Oral Law and halacha books. Jewish festivals as practiced today are similar in holiness to Shabbat. As with Shabbat, the Jewish festival has candle lighting, kiddush at two meals, and havdala.   We eat our best food and wear our best clothing on Jewish festivals (we eat our next-best food and wear our next-best clothing on Shabbat!).
The main idea behind eating meals on Jewish festivals is joy (simcha), so you should drink wine and eat meat (only if you enjoy wine and meat).  There is no third meal on Jewish festivals since people used to eat two meals each day (adding a third meal on Shabbat was for enjoyment/oneg).
 
Melachot
Any activities or actions permitted on Shabbat are also permitted on the Jewish festivals. Actions that are forbidden on Shabbat are generally also forbidden on Jewish festivals, but there are some leniencies (only if the actions are needed for that festival day).
Examples

• Lighting from an existing flame,
• Cooking and baking for the Jewish festival day, and
• Carrying outside the eruv (hotza'a--transferring objects between domains).

 
Grama
Grama (indirectly causing an action) is permitted on Jewish festivals (but not on Shabbat). For example, you may advance or delay a timer that will make a light go on or off in the future (the timer must already be plugged in and operating from before sunset of the festival day).
Note For an action to be considered indirect based on time, there must be at least 2.5 seconds after the first action is done before the resulting action begins to happen.

Psik Reisha Dla Neicha Lei
Psik reisha dla neicha lei is forbidden on Jewish festivals, just as it is on Shabbat.

D'oraita Restrictions
D'oraita restrictions apply world-wide to:

• First and seventh days of Passover,
• First and eighth days of Sukkot,
• First day of Shavuot,
• Yom Kippur,
• First day of Rosh Hashana.

Note The same restrictions apply to all other Jewish festival days but are rabbinical.
 
Women
In general, women are not required to perform the positive, time-dependent commandments. Women and girls are not required to eat any Jewish festival meals except the Passover seder meal (but they are not allowed to fast on those days).