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Knife Sharpening

The following is a record of the presentation given by Rabbi Doniel Neustadt, former Rosh of the Council of Orthodox Rabbis in Detroit, to the AKO Va’adim Convention in February 2009, as well as the comments of some of the participants.

Food service establishments regularly send out their knives for sharpening, and it appears that there are three potential kashrus concerns with this practice, as follows:

  • The sharpening company may give the establishment different knives than the ones which the establishment gave them for sharpening. This is an especially likely in cases where the sharpening company actually owns the knives and lends them to the establishment in exchange for the rights to sharpen them. This issue can be avoided if the Mashgiach has a tevias ayin on the knives and/or marks them.
  • Knives are typically very dirty when they arrive at the sharpening facility, and therefore all knives are washed in hot water or a dishwasher before the sharpening begins. This potentially allows non-kosher b’lios to get into the kosher knives. See below for more on this.
  • The same machine is used to sharpen the (clean) kosher and non-kosher knives, and the friction created by the process does heat up the knives somewhat. If that heat would be above yad soledes bo, there would be a potential for b’lios to transfer between the machinery and knives. However, in tests which Rabbi Neustadt performed in one sharpening company, the sharpening wheel and the cooling water (where that was used) were consistently cooler than 100° F and were not hot to the touch. As such, it appears that this does not pose a serious concern.

As noted above, the simplest way to guarantee that the sharpening company returns the kosher knives to the establishment is to mark the knives and check them when they return. As for the second issue, that the knives might be washed in hot water before sharpening, a number of suggestions were given:

  • Rabbi Neustadt arranged a vendor who has knife sharpening equipment mounted on a truck services would service the kosher stores in Detroit. He washes the knives in the store, sharpens them in his truck right in front of the store, and then gives them right back. This avoids all kashrus issues (although they are not makpid that he use different sharpeners for dairy and meat).
  • Rabbi S. H. Adler reported that in Toronto they have installed a deep fryer in one sharpening company, and a COR Mashgiach uses it to kasher all knives before they are sent back to the establishments. The Mashgiach is requested to come to the sharpening company approximately every 2 weeks, the deep fryer is locked/sealed whenever he is not there, and he seals the knives before they are sent to the stores.
  • Rabbi Z. Blech said that in establishments that he certifies, all knives are kashered when they return from the sharpening company.