1. ידות לטומאה (to contract or transmit tumah, but not to combine for a shiur)

A Mishnah teaches the principle of ידות – “handles,” i.e., items which serve as handles for food, regarding tumah: כל שהוא יד ולא שומר – anything attached to food which is a יד and not a שומר (such as a bone without marrow with meat at its end) טמא ומטמא ואינו מצטרף – contracts tumah to the food, and transmits tumah from the food, but does not combine with the food to comprise the minimum shiur for tumah. A שומר, even if it is not a יד, contracts and transmits tumah, and also combines with the food for a shiur. ידות are derived from the word "לכם" – for you written regarding זרעים – seeds (i.e., food), teaching that tumah applies לכל שבצרכיכם – to all your needs for food, including handles. A lengthy analysis explains why this derashah was written regarding זרעים, neveilah, and ovens, and seeks the source that not only can ידות transmit tumah from food, but even contract tumah to food. It concludes: מעיקרא כי כתיבא יד אהכנסה כתיבא – originally, when "יד" was written in the Torah, it was written regarding importing tumah to food (which is the subject of the passuk of זרעים). [This is extended to שומר through a kal vachomer, since a שומר protects food.] An additional explanation is offered.

1. Machlokes whether יד is effective for הכשר

Rav said: יש יד לטומאה ואין יד להכשר – there is a halachah of יד regarding tumah, but there is no halachah of יד regarding “preparation” of food for tumah through moisture. Thus, if water touches the stem of a fruit, the fruit does not become susceptible to tumah. Rebbe Yochanan says a יד is effective even for הכשר. This machlokes may hinge on the derashah quoted above ("לכם לכל שבצרכיכם"), and they disagree whether מקרא נדרש לפניו ולפני פניו – a passuk is darshened to explain the phrase before it, and also the one before the phrase before it (in this case, "וכי יותן מים" – but if water had been placed, referring to הכשר). Alternatively, they disagree in סברא: Rebbe Yochanan holds הכשר תחלת טומאה הוא – הכשר is considered the beginning of tumah, so the halachah of ידות applies to הכשר as well, and Rav holds הכשר is not the beginning of tumah. A Baraisa supports Rebbe Yochanan’s view.

1. Machlokes if there is a minimum shiur for שומר and יד

Rav said: אין יד לפחות מכזית – there is no יד for less than a כזית of food, ואין שומר לפחות מכפול – and there is no שומר for less than a [large] bean’s volume. Thus, if a יד is attached to less than a כזית of food, the יד is ineffective, and tumah touching the יד will not be metamei the food. Likewise, less than a כפול of food is not significant enough for its שומר to be effective, and tumah touching the שומר is not metamei the food. Rebbe Yochanan disagrees and says יש יד לפחות מכזית, and יש שומר לפחות מכפול. However, although he holds a שומר has no minimum shiur, he concedes that a יד does require a minimum shiur, but holds the minimum is a כפול, not a כזית.