A basic phenomenon in chemistry plays a crucial role in industrial kashrus. When two chemicals react with one another, one will be used up before the other. The chemical used up first is called a “limiting reactant” and the chemical which is not used up is an “excess reactant”. Often the excess reactant is recovered, purified, and used again in another production.
Consider a scenario in which the limiting reactant is non-kosher, the excess reactant is kosher, and the heat needed for the reaction is 200 Fahrenheit. The excess reactant, after the reaction, becomes non-kosher. It is recovered and used in a different reaction. Without knowledge of the previous reaction, a mashgiach may believe that the ingredient is as kosher as it was originally.
This scenario is not academic. One example of the reuse of an excess reactant is in the production of a chemical compound called a methyl ester. Methyl esters are used in the production of sucrose polyester, which is used as a fat replacement in some well-known snack products.
In a non-kosher version of this production, methanol, which is a petrochemical, is reacted with tallow. Methanol is the excess reactant and tallow is the limiting reactant. Methanol recovered from the reaction is purified and reused in future methyl ester production:
Another reaction involves lard with acetic acid (also a petrochemical). The acetic acid is the excess reactant. In this case the excess acetic acid is not reused in the same process but returned to the original acetic acid supplier:
This practice prompted the IAR to review the global acetic acid industry to determine whether acetic acid could remain a group one (it turned out this practice was unusual, if not unique, and that the “dirty” acetic acid was being added not to virgin glacial acetic acid but to a side stream product).
A variation on the practice of reusing ingredients involves recycling a solvent for both kosher and non-kosher ingredients. A solvent is a liquid used to separate certain ingredients from a substance while leaving others behind (when we put tea leaves in water, water is a solvent for the flavor, color, caffeine, and other organic compounds). Solvents can be used in industrial food production to “wash” impurities from a product. Isopropanol is used to remove impurities in the production of xanthan gum. Dichloromethane is a solvent in the vitamin encapsulation process. Ethanol, water, and other liquids are also solvents in industrial production.
Solvents are sometimes used through multiple productions. Thus, a Rav Hamachshir for a Pesach production that uses a solvent should not merely determine whether the solvent is, itself, kosher for Pesach. He must also determine whether it has been used in a previous production.
An excess reactant destined for a second production or a reusable solvent may be toxic and objectionable – so foul that even a dog would think twice before eating it. The question of using such a substance that already absorbed חמץ or איסור is a שאלת חכם.
Finally, it is worth reminding ourselves that tracking rework should be on a mashgiach’s checklist. Manufacturers of margarine, ice cream, dressings and other foods do not throw away product simply because it does not meet their specifications. Rather, imperfect product is often reworked and reprocessed in a subsequent run. Confirming that all raw materials are in fact “raw” will eliminate any complication.