Mi Yodeya is a question and answer site for those who base their lives on Jewish law and tradition and anyone interested in learning more. It only takes a minute to sign up.
Sign up to join this community
Is there a scientific explanation for the concept of "blias issur" absorption of taste in pots. Like for example if since heat expands materials maybe the taste creeps in.
(I'm not asking about whether today pots and pans absorb, rather I am asking if the concept has a scientific explanation)
Repost from Dave
From a Kosher Spirit interview with Rabbi Chaim Cohn:
KS: Can you share a unique experience that you had while working at the OK?
RCC: I once had an argument with a plant engineer concerning whether or not stainless steel can absorb or not. He maintained and brought extensive documentation to prove that stainless steel can’t absorb anything and therefore should not need kosherization. I told him, your proofs are impressive but the Rabbis decreed 2000 years ago that metal needs kosherization and I do not have the authority to go against them. We agreed to differ.
Approximately a year later, I was in the process of supervising the kosherization of a 1000 gallon reactor and after the workers had meticulously cleaned it we brought it to a boil. There was about a quarter of an inch of scum on the top of the pot. The engineer was passing by and I called him over to look at it. I said, “This was a completely clean pot.” I turned to the workers and asked, “Right?” The workers nodded their heads vigorously up and down. The engineer looked at it and said, “ I can’t argue with empirical evidence,” and walked away.
Six months later I got a call from the engineer. He said, “Rabbi Cohn, I now understand.” “Great,” I thought, and asked, “You now understand what?” He answered, “I understand why a stainless steel vessel will absorb.” I asked, “Why?” He answered, “You have to understand, when it leaves the factory it can’t absorb anything, however, when it is heated it expands and contracts and it will produce micro fissures. Your Rabbis were right, you can’t measure this and therefore have to assume the worst-case scenario that the entire volume has absorptions in it.”
As far as I know (from experience around the industry) this is a generally recognized phenomena. Consider Flavor Scalping, where the packaging absorbs the flavor of the contents and vis-versa. Now, I'm sure in the details the Halacha is way more strict in many cases beyond a scientific understanding of the situation, but the basic notion is certainly well known in the food industry.
Yes, food engineers generally don't think stainless steel absorbs, but stainless steel is a modern invention not discussed in Chazal. Other materials have different characteristics.
Wood barrels are used in some alcohol making specifically because they want the flavor transfer into the food product. The transfer isn't only one-way, and that itself can be reused to make other alcohol after the absorption has occurred.
All of the above more speaks to Kavush - leaving materials at rest over a long period of time. But part of the effect is kinetic (as described in the source of the first link), and the rate of diffusion increases under heat.
All of the above is for polymers, primarily, but the idea that this diffusion happens with some other materials is recognized in the industry, as far as I understand.
Surprisingly enough, proteins (such as those found in food, especially in meet) have a great affinity in binding to steel surface layer. On top of this, proteins also tend to affect the chemical composition of the stainless steel surface, by selectively releasing metal ions from the stainless steel alloy.
https://en.wikipedia.org/wiki/Protein_adsorption
The following article delves into some details regarding the effect of albumin (a protein commonly found in milk and blood) on stainless steel vessels:
