Dishwashers may generally not be kashered except when made of stainless steel (and have no non-kasherable materials inside, such as plastic, silicone, or rubber).

You may not use cooking utensils on Passover that have been used for cooking chametz during the year unless they have been kashered. For details, click kashrus/kk-passover-kashering.htm">here.
You do not need to sell the chametz that is on the utensils unless it totals more than 1.3 fl. oz. (39 ml, or 1/6 cup).

You may make certain utensils kosher for Passover if they were chametz or non-kosher. For a list of materials that can be kashered, see the sections entitled "Items/Materials that Can Be Kashered" and "Items/Materials that Cannot Be Kashered" here: Introduction to Food Nullification: Utensils (Kashering).

A hot (120° F--49° C--or more), wet utensil transfers its gender to a countertop upon which it is placed, but only at the area of contact.
Status of Countertop

1. Gender status of the countertop:
   • D'rabanan, the countertop area of contact remains that gender until kashered (as long as the countertop material is kasherable).
   • D'oraita, the countertop reverts to kosher-neutral/pareve after 24 hours.
   Note If the utensil and counter were not wet (nor dirty with food) at the area of contact, there is b'di'avad no transfer of gender.
2. If you put a hot, wet utensil of the opposite gender on that same spot, that counter space may become non-kosher.

Status of Utensils
If the counter had not had a hot, wet utensil/container of food of the opposite gender placed on the same spot within 24 hours of each other, the utensils may be used and the utensils are still kosher.
Status of Food
This does not apply to food that is directly placed on the counter, in which case the food might become non-kosher.
 

Food Nullification in Utensils: Torah-Law and Rabbinic Decree
By Torah law (d'oraita), any clean utensil, countertop, etc., automatically reverts to neutral/pareve and kosher after not being heated to more than 120° F (49° C) for 24 hours.
But by rabbinic decree, utensils do not automatically become neutral/pareve even after 24 hours and must be kashered by heat (libun—direct heat; hag'ala—boiling in a pot; or eruy rotchim—pouring boiling water over item) or, if some types of glass, by soaking in water (meluy v'eruy ).
 
Changing Gender of Utensil
You may kasher a pot or cooking/eating utensil from:

• Non-kosher to kosher, or
• Year-round use (chametz) to kosher for Passover.

 
You may not intentionally kasher a utensil in order to change it from dairy to meat or meat to dairy; you must first kasher it from accidentally (or intentionally) non-kosher to kosher/pareve, or from non-Passover to Passover/pareve. You may then use it for either dairy or meat.

Once you have used it for that gender, the item retains that gender (unless you re-kasher it for Passover or you make it non-kosher first, then kasher it to neutral/pareve).
But if you accidentally heat meat with a dairy utensil or vice versa, you may kasher it back to its original gender by any one of the kashering methods, depending on how it became non-kosher.
 
Items/Materials that Can Be Kashered
The following materials can be kashered:

• Glass, including Corelle, if not used directly on the stove or oven. Glass does not change gender or other kosher status unless heated on a flame or in the oven. Unless it is heated in this way, glass does not ever need to be kashered (except for Passover) (see Meluy v'Eruy, below).Glass, including Corelle, if not used directly on the stove or oven. Glass does not change gender or other kosher status unless heated on a flame or in the oven. Unless it is heated in this way, glass does not ever need to be kashered (except for Passover) (see Meluy v'Eruy, below).Glass, including Corelle, if not used directly on the stove or oven. Glass does not change gender or other kosher status unless heated on a flame or in the oven. Unless it is heated in this way, glass does not ever need to be kashered (except for Passover) (see Meluy v'Eruy, below).

• Granite (not granite composite)
• Marble
• Wood, if smooth (see notes on Eruy Rotchim, below)
• Metal, including stainless steel, cast iron, and aluminum.

Note While metal can be kashered if thoroughly cleaned, welded handles and other difficult-to-clean parts may render a metal utensil not kasherable. You might be able to use libun kal on the problematic area and still use hag'ala for the remainder of the utensil.
 
Items/Materials that Cannot Be Kashered

• China
• Corian
• Corningware
• Crockpot
• Formica
• Glass that has been used directly (kli rishon) on a stove or in an oven; however it can be kashered in a kiln
• Granite (composite)
• Knives with Plastic Handles (knives with wooden handles may be kashered if there are no cracks in the wood and if the rivets do not have spaces that catch food and prevent you from cleaning it completely)
• Mixer-there might be exceptions. Consult a rabbi.
• Plastic
• Porcelain (Enamel)
• Pyrex (if used directly on stove or in oven--kli rishon)
• Rubber (synthetic)
• Silestone
• Silverstone
• Stoneware
• Teflon
• Toaster/Toaster Oven
• Waffle Iron.

 
Pot Lid Handle
Kashering
The handle on a pot lid does not need to be kashered for normal use during the year. 
Reason It does not normally get hot.
Cleaning
However, the pot lid handle must be removed and the lid cleaned where the handle attaches, if possible.
Note If the gap between the handle and lid cannot be completely cleaned, you may not use that lid for Passover and you normally may not kasher it if it becomes non-kosher. If the lid handle cannot be removed, consult a rabbi.

Pot or Pan Handle
A plastic handle that gets hot, especially if it is over a flame on a burner, may not be kashered. If the handle becomes non-kosher, it must be replaced. If a plastic handle connects directly to the metal of the utensil, consult a rabbi about what to do.
 
Food Nullification: Heat-Kashering
Three Methods of Heat-Kashering
Heat-Kashering is of three types:  Libun, Hag'ala, and Eruy Rotchim.

1. Libun (Direct Heat)
   How It Works  Burns up any residual food taste

       

• 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 does not need to burst into flame, just to smolder), or
• Put the pot into the oven at 500 ° F for 40 minutes. (First, remove any non-metal handles; they will need to be kashered separately or not used.)

   

2. Hag'ala (Boiling)
    

• Boil Method Boiling water within the pot to be kashered, and making the boiling water overflow, or
• Dip Method Dipping a smaller pot or utensil to be kashered into a larger pot of boiling water.

       

• If the pot in which you are kashering the items had been heated to 120° F (49° C), with food of that gender in the pot, or more within the previous 24 hours, the items you are kashering will assume the gender of the pot.
• If the pot in which you are kashering the items had NOT been heated to 120° F or more for at least 24 hours, any items that are kashered in it will become kosher and pareve.

     
 

3. Eruy Rotchim (Hot-Water Pour)

         

 
Food Nullification: Meluy V'Eruy
Meluy V'Eruy To Kasher Glass
Halachically, “glass” includes Arcoroc, Corelle, crystal, Duralex, and Pyrex.
NOTE In pre-war Europe, where glass was expensive and hard to obtain, it was customary to kasher drinking glasses, especially for Passover, by soaking the glasses for three 24-hour periods (meluy v'eruy), as follows:
Step 1: Submerge glasses in cold water for 24 hours.
Step 2: Empty water, refill, and submerge glasses again.
Step 3: Repeat Step 2.
NOTE If any of these materials were heated directly on a flame or other heat source, they cannot be kashered by meluy v'eruy!

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).

If a microwave oven's walls/floor/door do not become hot (more than 120° F, or 49° C), the microwave oven does not become non-kosher, dairy, meat, or non-Passover/chametz.

A microwave oven that does not normally get hot, may get hotter than 120° F if you cook:

• A liquid or moist food for a long time (even if less than 10 minutes),

• Several liquid or moist items sequentially, or

• Popcorn and similar foods.

If a microwave oven's walls/floor/door get hot, the oven can become dairy, meat, or non-kosher (if they become one gender and then the opposite gender is cooked or if non-kosher food has been cooked in it). If any surface--including walls, door, floor, etc.--that gets hot are plastic or coated metal, it cannot be returned to kosher or pareve. However, if the surfaces are all made of metal, they may be kasherable. Consult a rabbi.

WERE BOTH FOOD AND UTENSIL LESS THAN 120° F?
YES
What to Do Wash off with cold water and soap.
Status Everything is kosher and may be used immediately.
 
NO
WAS THE UTENSIL CLEAN AND UNUSED at 120° F or more FOR MORE THAN 24 HOURS?
Note Clean means no residual food, including pareve; this IS essential since the food or utensil or both were hot! If used at 120° F or more for pareve within 24 hours, ask a rabbi.
YES
Status

• Food is kosher
• Utensil requires kashering. 

What to Do

• Wash utensil with cold water and soap.
• Wait 24 hours after the spill occurred before kashering it.

Note If you wash off the utensil with hot (above 120° F) water, you must wait 24 hours after cleaning the utensil before kashering it.
 
NO
IS THE SPILLED FOOD LESS THAN 1/60th of the volume of the commonly used capacity of the utensil (if the utensil is empty) OR less than 1/60th of the actual volume of food contained within the utensil?
YES
Status

• Food is non-kosher.
• Utensil is kosher.

What to Do Wash utensil with cold water and soap and wait 24 hours before using the utensil.
Note If utensil had food in it and the spilled food was less than 1/60th of the volume of the food in the utensil, you may use the utensil immediately after cleaning it and you need not wait 24 hours.
 
NO (Spilled food was 120° F or more, utensil not clean, utensil used within 24 hours, spilled food is more than 1/60th of the utensil's volume)
Status

• Food is non-kosher.
• Utensil is non-kosher.

What to Do Utensil must be kashered.  See Hag'ala/Boiling or Libun/Direct Heat for instructions on how to kasher each material.



Note In this section, meat spilled onto a dairy utensil and dairy spilled onto a meat utensil are treated the same.

WERE BOTH FOOD AND UTENSIL LESS THAN 120° F?
YES
What to Do Wash off with cold water and soap.
Status Everything is kosher and may be used immediately.
 
NO
WAS THE UTENSIL CLEAN AND UNUSED at 120° F or more FOR MORE THAN 24 HOURS?
Note Clean means no residual food, including pareve; this IS essential since the food or utensil or both were hot! If used at 120° F or more for pareve within 24 hours, ask a rabbi.
YES
Status

• Food is kosher
• Utensil requires kashering. 

What to Do

• Wash utensil with cold water and soap.
• Wait 24 hours after the spill occurred before kashering it.

Note If you wash off the utensil with hot (above 120° F) water, you must wait 24 hours after cleaning the utensil before kashering it.
 
NO
IS THE SPILLED FOOD LESS THAN 1/60th of the volume of the commonly used capacity of the utensil (if the utensil is empty) OR less than 1/60th of the actual volume of food contained within the utensil?
YES
Status

• Food is kosher.
• Utensil is kosher after 24 hours.

What to Do Wash utensil with cold water and soap and wait 24 hours before using the utensil.
Note If utensil had food in it and the spilled food was less than 1/60th of the volume of the food in the utensil, you may use the utensil immediately after cleaning it and you do not need to wait 24 hours.
 
NO (Spilled food was 120° F or more, OR the utensil not clean, OR the utensil was used within 24 hours, and spilled food is more than 1/60th of the utensil's volume)
Status

• Food is non-kosher.
• Utensil is non-kosher.

What to Do Utensil must be kashered.  See Hag'ala/Boiling or Libun/Direct Heat for instructions on how to kasher each material.

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.

BAKING IN NON-KOSHER OVEN

An oven that has not been used for at least 24 hours is considered, d'oraita, to be neutral/pareve, but only if it is clean. D'rabanan, it is still not kosher, but this may be useful for when you can be lenient; e.g., if there is a safek.

Note Even when baking in a non-kosher oven, you must cook the food in a kosher utensil.

INTRODUCTION TO BAKING IN NON-KOSHER OVEN

Baking in a Non-Kosher Oven

How To Tell if Oven Is Clean

To determine whether a non-kosher oven with black or brown spots is clean, scratch them:

• If the substance crumbles, the spots are OK and you may bake non-liquid food in that oven without covering the food.
• If the spots do not crumble or they remain immovable or come off in flakes rather than crumbles, consider the oven not clean.

Uncovered Food; Clean (Non-Kosher) Oven

You may cook food uncovered in a non-kosher oven if:

• The oven rack and walls are clean, and
• The food is not “liquid.”
  
  Note Non-liquid is defined as not being liquid before cooking OR not being liquid after cooking, but the food does not need to be non-liquid at both times.  Examples of “non-liquid” foods:

  • Apple cobbler
  • Lasagna
  • Meat (that will create gravy at the end)
  • Pudding
  • Raw fish.

What To DoPlace two layers of foil under the baking utensil.

Double Wrapping

When To Double Wrap

Double-wrap food before baking in a non-kosher radiant-heat oven if:

• The rack and/or oven are not clean;
• The food that you are baking is liquid at any time during the cooking process; OR
• Some of the food you are baking spills onto the rack or oven surfaces.

How To Double Wrap

When wrapping food for cooking in a non-kosher oven, the wrapping material does not need to seal completely, but the:

• Food must be completely covered with two layers of foil or plastic;
• Layers must keep water vapor out from between the layers; and
• Surfaces of the utensil must all be covered.

If you have a non-kosher food utensil, kasher it before you immerse it in a mikva (tevila).
 

You may kasher oven racks by putting them in a self-cleaning oven and running the self-clean cycle. Or, clean with oven cleaner and then put into a normal oven on its highest temperature for 40 minutes.

To kasher a gas stove:

• Remove the burner grates,
• Clean off any deposits,
• Place the grates on a clean surface inside the oven, and
• Heat the grates to the oven's maximum temperature for 40 minutes.

 

To kasher an oven for Passover:

• Clean it completely, including any hard deposits, and
• Heat the oven for 40 minutes at its highest temperature.