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The following is from an article posted on the CRC web site at
<a href="https://goo.gl/ispg9T" eudora="autourl">https://goo.gl/ispg9T</a>
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Food service establishments regularly send out their knives for
sharpening, and it appears that there are three potential <i>kashrus</i>
concerns with this practice, as follows:
<ul>
<li>The sharpening company may give the establishment <u>different</u>
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 <i>Mashgiach</i> has a <i>tevias ayin</i> on
the knives and/or marks them.
<li>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 <i>b’lios</i> to get into the kosher knives. See below
for more on this.
<li>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 <i>yad soledes bo</i>, there
would be a potential for <i>b’lios</i> 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.
</ul>See the above URL for more.<br><br>
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