Sunday, January 24, 2010

The Science of Kashrus

Cooking milk and meat dishes (or kosher and non-kosher dishes) in the same oven creates a number of problems vis a vis the laws of kashrus. The biggest problem is when this is done simultaneously and there is the possibility of direct transfer of material from one pot to another. Most problematic is when one pot is above another, or when one is touching another. But even without direct transfer of actual food substance from one dish to another, there are two issues that one must be concerned: aroma and steam. Aroma (reicha milsa) is considered significant under certain circumstances. Thus, one may not cook a fatty meat in a small oven, unventilated oven at the same time as a dairy dish, even if the pots are not touching each other. This is due to transfer of aroma. The prohibition is a priori (l'chatchila), however. If done ex post facto (bedieved) it may be permitted (ask your LOR.)

Steam (zeiah) is a more interesting issue, in my opinion, for the steam of a liquid has the same status as the food from which it was derived. This has implications for not only cooking milk and meat dishes separately, but when cooking one after the other. Thus, the steam from a meat dish will rise up to the roof of the over and make it fleishig. Afterward, if one cooks an uncovered milk dish in the over, the steam will rise up, absorb the meat taste from the roof, and drip back into the milk dish. Uh oh, basar v'chalav - treif!!! So, if one does not have separate ovens for milk and meat, one should "designate" the oven for - say - meat, and ensure that when cooking milk the pot is always covered.

Obviously, this is an oversimplification, since there are issues like bitul, nosem taam lifgam, etc. Again, ask your LOR. (Or Rabbi Abadi, who says that there is no such thing as a "fleishig oven".)

But let's come back to a sentence which should have made you pause. The steam of a liquid has the same status as the food from which it was derived. If you just glossed over it, here is what it is saying: if one distills water from milk, the water is considered milchig. If one distills water from chicken soup, the water is considered fleishig. Now, for those who don't remember their elementary school science, distilled water contains nothing but water. Distilled water from milk is indistinguishable from distilled water from chicken soup, or from dog soup, or from industrial waste.

According to wiki, the knowledge of distillation was known in Mesopotamia at least back to the 2nd millenium BCE. So why don't the poskim (who rely on the Rosh who relies on a mishnah in Machshirim) seem to know about this??

Addendum! I should have done a search on this topic before posting it, but please also refer to this entry by Orthoprax, posted over three years ago.


Anonymous said...

Come on! It works just like homeopathy where the water magically retains knowledge of its pre-dilution state!

Anonymous said...

As a chemical engineer with almost two decades of work experience, I feel I can address distillation as your approach is oversimplified. In distillation, components having higher volitilities are evaporated from solution and then condensed into a solution having a higher volitility. The chemicals that give food its taste and smell are known as esters and are molecules with varying degrees of volititity.

To separate esters from water vapor one would require a distillation column in which different volitilities are separated from each other. An oven in the presented scenario, however, is a batch distillation and is incapable of separting all, or even the majority, of esters from the condensed water vapor. To do so, one would have to run the ove over several warm-up/cool-down cycles.

Therefore, one is left with a modified milk or meat vapor that then condenses. If, however, we could a distillation could, one plate (see bubble plate distillation) would be pure water while other plates would be a combination of water and food flavor.

Frum Heretic said...

Thanks for the clarification and correction on my oversimplification. I am aware that we are not talking about a precise distillation process here. So tell me, what kind of milk products - and how much of it - could one expect to find in a (poorly) distilled milk vapor? Could one taste it or detect it by other than a sophisticated analytical process, such as a gas chromatograph? Regardless of how little there is, it still has the status of milk or meat.

(Also by way of clarification since you mentioned smell, folks should realize that volatiles that impart smell are measured in parts per million and parts per billion. Amounts that are otherwise never an issue in kashrus. Unless, of course, such a minute amount actually imparted a taste. But let's ignore smell and stick to actual meat or milk compounds in a condensed vapor.)

Anonymous said...

I really can't answer your question because I've never tried to evaluate the distillate of either milk nor meat vapors. I am not sure one could taste milk or meat flavors in condensed vapors. Nonetheless, I would not say that it is beyond reason that one could assume that vapor might have some flavor. Remember much of what they are doing are thought exercises. Similarly, I haven't a clue whether on fifty-ninth milk/meat mixture tastes different than a one sixtieth mixture.

zach said...

Yeah, doesn't make too much sense. Even given Chemical Engineer Anonymous' comment, there would certainly be bitul. It's probably just a gezerah with no scientific basis.

I wonder if water distilled from milk in the laboratory is still considered milchig?!

Frum Heretic said...

Anonymous Chemical Engineer, thanks for your thoughtful comments. Also keep in mind that bitul is ultimately based on taste, so that even if taste were imparted by 1 in 10,000 it would considered significant.

zdub said...

Check out this discussion:

It isn't just Rabbi Abbadi that is lenient! Aruch Hashulchan and Rabbi Hershel Schachter allow consecutive cook of milk and meat uncovered (I presume, since RMF's opinion is brought also, and he says that one pot should be covered.)

Shlomo said...

But even if the water was completely distilled as per chemical engineer it would still be considered milchik or flaishik as per its previous state