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.

A non-spicy/non-charif liquid or food with any liquid (enough to pour, but that may be even one drop) that sits for 24 hours or more will transfer gender or non-kosher status to its container.
Situation Dairy or meat liquid-containing food is in pareve container.
StatusContainer will become dairy or meat (regardless of intention). 

All beer in the USA is kosher and does not need supervision. Many beers in other countries are also kosher even without supervision, but the status should be checked with local kashrut authorities.
Situation Some beers have lactose added.
Status If the lactose is less than 1/60^th of the total volume, the beer is not considered to be dairy.

Microwave oven floors can get hot, especially where there is no rotating glass tray and the utensil is placed directly on the oven floor. All microwave ovens should be assumed to get hot unless you have tested them personally.
Microwave Floor
Cover the floor (ideally with styrofoam or another substance that blocks heat and moisture).

Glass Tray
The glass tray does not become non-kosher and does not become dairy or meat or chametz (unless it was removed and used in a conventional oven) as long as it is clean.
Plastic Tray Support
The plastic support under the glass tray must be cleaned and must be blocked from contact with actual cooking utensils and from food if the tray:

• Has any food of the gender opposite that of the food being cooked,
• Has non-kosher food on it, or
• Is dirty and you cannot tell with what.

Food soaked in brine, vinegar, or any spicy liquid for long enough to be cooked if heated on a burner or in an oven will absorb or transfer gender or non-kosher status from/to any utensil used with it.

When a spicy/charif food takes on the gender of the cutting/squeezing utensil:

• You may not cook or eat that food with food of the opposite gender.
• However, you MAY eat the opposite-gender food immediately after eating the gendered spicy food without waiting.

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).

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!

You must be able to recognize, from at least one piece, that an ingredient is from the ground or from a tree in order to say borei pri ha'adama or borei pri ha'eitz. If not, say she'hakol.
So say she'hakol on:

• All foods that did not grow in the ground or on a tree, but also
• Foods that you cannot personally identify as having grown in the ground or on a tree—either because it has been finely ground or processed or because you personally do not know what it is.

Shavuot (Yom HaBikurim in the Torah) celebrates and commemorates the giving of the Ten Commandments to the Israelites at Mt. Sinai.
Beginning with the second night of Passover, the Israelites who left Egypt underwent 49 days of spiritual improvement and purification until they were ready to receive the Torah from God (Shavuot ends this 49-day “omer” period).  We can undergo a similar process of spiritual development each year during these 49 days (how to do that is beyond the scope of this website). According to our tradition, the Israelites in Egypt had sunk to the 49^th level of spiritual impurity (tum'a). The Israelites had to raise themselves in 49 daily stages to be worthy of receiving the Torah.  Several books and siddurs portray the 49 days of the omer as corresponding to the Seven Sefirot embedded in the seven weeks.  This awareness can help us work on and maximize the power inherent in each day of the omer to fix that particular sefira in ourselves. We thus relive this transition from slavery to freedom and the service of God each year as we try to perfect our midot (personal characteristics) to again be worthy of receiving the Torah on Shavuot.

 
Symbolism of the Shavuot Offering
In the Temple in Jerusalem, the only communal sacrifice of leavened bread was on Shavuot. Leavening in dough is compared to arrogance in humans (people puff themselves up to look more important than they actually are). During Passover we destroy, and refrain from eating, leaven--just as we try to destroy/remove arrogance from our personalities. After Passover, we continue to work on our personal traits (midot) until we reach Shavuot, when we celebrate receiving the Torah.  At Shavuot, we Jews have a right to feel important, since we are spiritually elevated by virtue of having been given the Torah.
 
Shavuot: Universal Customs
The universal custom is to eat at least one dairy food during Shavuot.
Possible reason  At the time the Israelites received the Torah, they did not have any kosher meat (they had not been required to eat kosher until then) and so the only food they were permitted to eat was dairy food.
Another universal custom is to stay awake all night (if possible) studying Torah.
 
Shavuot: Symbols
Unlike other Jewish festivals, Shavuot has no concrete symbols and no specific unique commandments/mitzvot, other than sacrifices that were brought in the Temple in Jerusalem.

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.

You should give charity daily (except Shabbat and Jewish festivals) at the time of prayer.

Begin saying L'David Adonai ori v'yish'i (Psalm 27) on the first day (at night) of Elul, not the first day of Rosh Chodesh Elul (the 30th of Av). The last day to say this Psalm is 22nd of Tishrei (Shmini Atzeret). This Psalm is recited twice daily, in shacharit after shir shel yom and in ma'ariv after alenu, including on Shabbat and Jewish festivals.