To maintain the separation of meat and dairy during cooking, the kosher kitchen must have at least two sets of utensils, one for meat and another for dairy foods.
This requirement includes dishes, flatware, pots, pans, and all other utensils used in the preparation, serving, or eating of food. Many homes will have at least some additional utensils for preparing pareve (parve) foods, especially baked goods. Using only pareve utensils for preparation and storage makes it easier to assure the continued neutral nature of the pareve foods.
The requirement to have two sets of utensils has to do with the materials from which the items are made.
Although many of the materials from which these utensils are made will seem impermeable to most observers, the rabbis of ancient times felt sure that minuscule amounts of food could become absorbed into dishes or utensils made of even marginally porous materials.
As a result, it became part of standard kashrut observance to maintain two separate sets of dishes, utensils, and pots and pans for cooking and serving.
To help keep things organized, it is imperative to choose patterns for flatware, dishes, and cookware different enough from one another to be easily distinguished. While correcting mistakes is almost always possible, choosing patterns that do not look alike helps avoid confusion.
It is best to choose pots and pans made by different manufacturers for meat and dairy use, thereby dramatically increasing the visible difference between the sets.
In order to maintain the proper level of separation, utensils should also be stored separately. Having separate and distinct cabinets and drawers is the best way to ensure that items are not used for the wrong food.
In the case of items that by their nature will be hard to distinguish from one another, such as cookie sheets or cutting boards, it is best to mark items clearly as being either dairy, meat, or pareve.
Marking with paint, etching, or using colored adhesive tags are all commonly accepted ways of marking utensils.
There is no need to have two sets of drinking glasses, however.
Because of its nature, glass is not deemed capable of absorbing even minuscule amounts of food and so cannot become either meat or dairy (Shulchan Arukh, Orach Chayim 451:26). Therefore, one may, technically speaking, use a single set of glass plates in a kosher home.
The predominant custom, however, is to have two sets of dishes, even glass, in order to maintain the look and feel of a kosher home and reduce confusion involving the use of other utensils.
The CJLS has ruled that Corelle® is considered to be glass (See CJLS responsa May Glass Cookware be Kashered). However, glass used for baking (including Corningware® and Pyrex®) or for stovetop cooking (such as Visions®) is not to be used for both dairy and meat foodstuffs.
Plastic containers or utensils should be designated for meat, dairy, or pareve use and may not be used interchangeably.
Soft or non-dishwasher safe plastics (such as Tupperware®) or disposable multi-use plasticware (such as GladWare® or Ziploc® storage items) should be marked upon use to ensure that they are reused with only the same type of food as originally stored in them.
There is no requirement for a kosher home to have separate stoves, ovens, refrigerators, freezers, or dishwashers.
However, care must be taken to prevent the mixing of meat and dairy when using appliances.
For example, if cooking meat, dairy, or pareve items at the same time on a stove, one must take care that food does not splash from one pot to another.
The simplest advice is to cook only one kind of food at a time. Similarly, only one kind of food should be cooked in an oven at any given time. Before switching from one kind of food to another, any spills should be wiped out of the oven.
If it is absolutely necessary, one may bake meat and dairy foods at the same time, as long as both pans are tightly covered.
A self-cleaning oven may be kashered by running a complete cleaning cycle.
The same rules that apply to regular ovens should be observed when cooking in microwave ovens. (A microwave oven can be kashered by microwaving a cup of water on high, see article on kashering appliances.)
With regard to refrigerators and freezers, as long as food is wrapped carefully and marked clearly, meat, dairy, and pareve foods may be stored on the same shelves.
Dishwashers present a special dilemma.
It would be simplest to have two, but this will rarely be feasible in most homes. In such cases, only meat or dairy dishes should be washed at a time.
In order to use a dishwasher for meat and dairy sequentially, it is recommended to run an empty cycle with detergent between full cycles. The same dish racks may then be used for meat and dairy.
Sinks should be treated similarly.
Only one kind of dish should be washed at a single time. All surfaces must be cleaned thoroughly between food types. The use of separate sink racks is highly recommended.
Freshly washed dish towels may be used with any type of dish.
Rather than constantly changing towels after a single use, however, many people have different color towels for meat and dairy use. The same is true of potholders.
A special law governs knives used to cut foods called davar harif—sharp-tasting foods such as onions or garlic.
These special rules apply because an item considered davar ḥarif is deemed capable of absorbing other foodstuffs, even in minuscule quantities (cf. Shulchan Arukh, Yoreh Deah 96:1–2 and Klein, p. 363).
Therefore, it is a good idea to use pareve knives to cut onions or to chop garlic, because using a meat or dairy knife would, depending on which knife was used, give the cut onion itself the status of a meat or dairy foodstuff.
Questions about the status of other foodstuffs with respect to its status as a davar ḥarif should be addressed to a rabbi.
It is a daunting task to transform a non-kosher kitchen into a kosher one.
Yet, while the process is labor intensive, each individual step is actually rather straightforward. The goal is simply to remove all non-kosher food and food residue. The information given below covers both the process of making a kitchen kosher and also how to proceed when mistakes occur.
Dishes, utensils, pots, pans, and other items must be cleaned thoroughly and then left unused for at least twenty-four hours before kashering.
One well-known custom is to bury flatware which needs to be kashered in the ground for a period of at least twenty-four hours. This practice has its source in the requirement for thorough cleansing before kashering.
(As campers know, the gritty nature of dirt makes for a useful scouring agent.) But although putting flatware into the ground or into a flowerpot is an acceptable method of preparing the utensil for being made kosher, it is not itself a valid method of kashering. (See article on How to Kasher Dishes.)
There is a custom in some communities of taking new pots, pans, dishes and other utensils to be immersed in a mikveh, ritual bath, before use.
The Committee on Jewish Law and Standards has ruled that this is not necessary. Should one choose to do such immersion, a blessing is not required. (See The responsum, Tevilat Kelim, written by Rabbis Mayer Rabinowitz and Avram Reisner and relating to Shulchan Arukh, Yoreh Deah 120:4.)
Adapted with permission from The Observant Life.