Jew Food, Part III: In Which Things Get Ridiculously Complicated.

Important note to readers: This entry is not a guide to kashering dishes or utensils, nor as an any kind of authority on answering halakhic questions on kashrut. If you landed here by asking Rabbi Google a halakhic question regarding kashrut, I would encourage you to ask a local human rabbi 😉 (most of them don’t bite!) or at least consult a website run by halakhic authorities that you trust. (In the meantime, welcome to Letters to Josep! Have a kosher lemonade and enjoy the blog! 😉 ) Chabad has a good, reliable, comprehensive guide to kashering a kitchen here.


Dear Josep,

So, we’ve covered the issues with animals and animal products, and with plants and their products. None of this has explained why I answered “no” when you asked me if I could eat something made of kosher ingredients that you would cook in your kitchen, nor why I couldn’t simply eat the vegetarian food I was offered at the conference.

The reason for this can be summarized in one halakhic term: ta’am, which translates as “flavor”.

What does it really mean, the sages asked themselves, to avoid eating a certain type of food? What of the experience of eating a non-kosher product is prohibited? So the answer in our tradition is that it is the flavor, the ta’am, of the non-kosher product, that we must avoid. This principle expresses itself in how we answer questions about the level of separation between non-kosher and kosher food and meat and milk.

The problem, of course, is that if it’s the flavor that makes the difference, how are we supposed to make a ruling about something if we can’t actually taste it out of concern that it may not be kosher?! Sephardim actually hold that you can give the food to a non-Jewish cook (or someone else who is involved in the food industry and has an incentive to give an accurate answer) and rely on his answer about whether the flavor of the non-kosher product is discernible. But for the most part, we rely on the following principles:

K’Bol’o Kakh Polto–“As It Absorbs, So It Emits”

This is the principle about the utensils we use to cook and eat the food. Halakhically speaking, utensils absorb the flavors of the food that was cooked or served on it, as long as the food is hot. How hot? The sages say: yad soledet bo; basically, too hot to comfortably touch. Aside from temperature, there is also harifut; strength of flavor. Some foods are considered to have particularly strong flavors, such as onions, garlic, and citrus fruits. Those transfer their flavor even without heat.

Practically speaking, this means we have to have two sets of dishes and utensils: one for milk, and one for meat. We also have a bunch of pots and a big vegetable knife that are pareve (neither milk nor meat), so we can make food that can be eaten with either meat or milk. It also means that we can’t use any dish or utensil that has been used to cook non-kosher food, at least with hot food.

Our two sets of utensils. For some reason, blue became the accepted color to represent dairy, while red (for more obvious reasons) represents meat. You can often find your way around a kosher kitchen knowing this
Our two sets of utensils. For some reason, blue became the accepted color to represent dairy, while red (for more obvious reasons) represents meat. You can often find your way around a kosher kitchen knowing this “color code”. (Yes, I am aware that the dairy one is green. Close enough 😛 )

It is from this principle–that utensils absorb the flavor and emit the flavor the same way–that we learn how to kasher (=make kosher) utensils. So if I normally use a pot to cook food by boiling it, that means the flavors of that food can be removed by boiling water in the pot. If an oven absorbs flavor by its heat, you need to clean out the oven of any bits of food that might be stuck in it, and then leave it at its highest temperature for an hour or so. That’s the basic idea. Now I know what you’re thinking–oh, that sounds easy enough. Have you ever tried scrubbing every last inch of the inside of your oven? Unless you have a self-cleaning mechanism, this is really irritating and difficult work… I know because we have to do it every year for Passover. (Just wait ’til I tell you about the restrictions around Passover. 😛 ) Some things need to be torched (yes, with a blow torch) to burn out the flavor.

It should be noted that modern stainless steel is a lot less porous than the metals that were once used for things like this, so this is very, very strict and probably unnecessarily so. Sephardim hold that because glass is not porous, it cannot absorb flavors and therefore would not need to be kashered. (Unfortunately for me, Ashkenazim do not hold this way.) There is a rabbi in Hebron who, after reviewing a scientific study about the absorption levels in stainless steel, ruled that stainless steel should be considered like glass, but with the caveat that no one should hold this way unless another two prominent rabbis agree with him. As far as I know, this hasn’t happened yet.

Ta’am Lifgam (Unpleasant Flavor) and Ben Yomo (Of the Same Day)

Another principle is that the ta’am is only a problem if the flavor being transferred is desirable and pleasant. So, for example, if I’m washing dishes with hot water, and I accidentally use the meat sponge instead of the milk one, it’s okay because the dish soap gives it an unpleasant flavor.

This principle allows for the principle of ben yomo–the idea that after 24 hours, a flavor that was absorbed into a utensil is no longer pleasant. So for example, if I have a pot that was used to cook meat within the last 24 hours, if I cook dairy in it, even if it was clean, the dairy food is not kosher and the pot needs to be kashered. If, however, I cooked meat in it more than 24 hours ago, the pot will still need to be kashered, but the dairy food is okay to eat, because the flavor it absorbs from the pot is not a pleasant flavor.

Batel B’Shishim (Nullified In Sixty)

Friday morning. Eitan’s amazing Shabbat chicken soup is bubbling away on the stove. One of my curious little gremlins, who happens to be munching on a slice of cheese, quietly and stealthily slides the stepstool over to the sink, and before I have a chance to stop him–drops a bit of the cheese in the soup!

What will happen?

Can Shabbat be saved?!?!

A Shabbat without a bowl of this stuff is like a Christmas without Caga-tió!
In my household, Shabbat without a bowl of this stuff is like a Christmas without el Caga-tió!

…The answer is, probably. 🙂 According to the principle of batel b’shishim, the flavor of any given food becomes nullified–batel–when it is mixed with another food that is at least sixty times its volume. So in this case, I’d have to fish out the bit of cheese I could still see if it hadn’t melted completely into the soup yet, but as long as it was just a little bit and there was enough soup in the pot, and there is no recognizable cheese in the soup, then it’s batel and the soup is fine.


Note, however, that this rule does not count for foods that are considered harif (spicy or strong-flavored), for obvious reasons. You know what one clove of garlic or a squeeze of lemon can do for a dish. 🙂

To Summarize

The easiest way to think about this is to think of kashrut as a sort of “spiritual allergy”. Someone who has a severe allergy to peanuts or gluten can’t eat things that even have tiny traces of those foods, or that were processed in the same factory or cooked using the same utensils. Kashrut is actually less stringent than this after the fact, but the level of care we take to avoid any “contamination” of non-kosher foods or mixing of meat and milk is on the level of someone with severe celiac avoiding gluten. (I’m stepping away from the peanut allegory, because there are people who will have an allergic reaction just from sitting in the same room with someone who opens a bag of peanuts… as you know, I am perfectly content to sit in the same room as someone eating non-kosher food. 😉 )

And the bottom line, of course, is that keeping kosher is hard! 😛 I grew up with it, so it comes fairly naturally, but even so, every once in a while I’ll reach for the wrong spatula or pour hot food into the wrong mixing bowl. I know enough about the laws of kashrut that I usually know when something is okay, but when I’m not sure or I think it might not be okay, I relay the question to Eitan, who is ordained on this topic (meaning he is well-versed enough to give halakhic rulings on it). Sometimes even he will be stumped and will bump up the question to a higher authority, and give one of his rabbis a call.

This concludes our Great Jew Food Tirade! If you have any other questions about it, feel free to ask. 🙂

…Still convinced you’re going to kasher your kitchen for me if and when I come visit?! 😛 If you are, I clearly have not done my job! It may take a reading of this comprehensive guide to kashering a kitchen to properly dissuade you. 😉

But, as I was then, I am very touched by your intentions. I will be perfectly happy with sandwiches on paper plates if the occasion ever does arise. 😉

Lots of love,



Missed the previous installments? Here they are:

Jew Food, Part I: Vegetarians, Avert Your Eyes

Jew Food, Part II: The Vegan Section (well, sort of.)

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