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Q. I heard that the string used to hold together roasts can be chametz. How can string be chametz?
[A primary source for much of the information presented below, is Rabbi Yaakov Lach, author of Chullin Illuminated and manager of a twine and rope company.]
A. There is currently only one manufacturer in the United States who takes “dirty” cotton from the fields and converts it into twine. That manufacturer produces both regular and “polished” twine, and until a few years ago he would sprinkle flour onto the polished twine at the end of the process to help it dry. The application of flour was a very messy operation done in the part of the plant where the twine was wound onto the rolls, and invariably there would be a dusting of flour on the non-polished twine as well. Rabbi Wagshall (New Square) became aware of this and prevailed upon this manufacturer to switch from flour to ground marble (rock) powder.
There is no reputable information as to whether the same issue applies to twine manufacturers in other countries.
This type of twine is used by bakeries and is also sold to companies which use it to manufacture the netting which holds together pieces of meat. Due to concerns that the twine might have a dusting of flour on it, many hashgachos are particular that the twine used in a matzah bakery and the netting used in their packing houses must come from sources which are known to be free of this chametz concern.
That said, the actual concern of flour/chametz having an effect on the person’s food b’dieved, appears to be quite minimal if the person used netting made from unpolished twine. The halachic rationale for that position is that even if the twine was made in a factory that also uses flour, the ratio of flour to twine is assumed to be relatively small and is likely decreased each time the twine is wound/unwound or handled (e.g., when creating the netting, packaging it, putting it on the meat). Thus, the only concern is that a miniscule amount of flour remains on the netting, and then if the meat is cooked on Pesach, it will affect the meat. However, it would appear that any bit of flour left on the netting would be treated as already being in a mixture which is designated as being “lach b’lach” – either because it is mixed/absorbed into the actual netting or into the meat – such that it was already batel before Pesach. Lastly, there is only a safek if there is any flour on a given netting or piece of twine, and many are of the opinion that safek of an issur mashehu is batel even on Pesach. [See Shulchan Aruch OC 467:9 as per Magen Avraham 467:9, and other Poskim discussing that halacha.]
While these lines of reasoning justify the permissibility of the meat made in a netting of unknown status, it is appropriate that a hashgachah should be careful to only allow “approved” twine and nettings to be used in certified bakeries, stores, and packing houses.
A secondary (year-round) issue which was raised by Rabbi Elisha Rubin (OK) is that there are some nettings companies that submerge the nettings in a kosher-sensitive liquid so that the netting will be “quick release” or have other special features. It is worthwhile to pay attention to these issues when selecting a netting to be used in a kosher packing house.