Does food absorb a chametz ta'am if there is no heat (or equivalent) involved?

Question

This is a case where I am fairly certain that I know the practical halacha, but don't understand the issues underlying the practice.

Let's say you chop up some apples and nuts before Pesach on a chametz cuttingboard (that hasn't been used for several days prior), with a chametz knife (same), and store it in a new, never-used glass jar in your fridge. Can the apples and nuts be used on Pesach, for example as charoset?

My (limited) understanding is that the ta'am of a food is only transmitted from a vessel or utensil into the food item if heat is applied, or if the food has an intrinsic "sharpness" (like onions or radishes). And in any case the ta'am of the chametz would be stale at the time the food is prepared. Furthermore, we know that before Pesach chametz can be batel. So it would seem that there is really no reason one could not use such food on Pesach. And yet, I am sure that everyone would agree it may not be done. What am I overlooking?

A follow-up question: What if instead of charoset, you are making home-made sauerkraut? Again there is no heat, and no intrinsic sharpness in the cabbage. The only difference here is that the chopped cabbage is pounded to soften it and bring out the brine, before being allowed to ferment. Does either the act of pounding, or the natural fermentation process, behave analogously to heat insofar as the transmission of ta'am is concerned?

Answer 1

You write

So it would seem that there is really no reason one could not use such food on Pesach. And yet, I am sure that everyone would agree it may not be done. What am I overlooking?

The first part of your statement was correct. You can actually use this food on Pesach if the cutting board and knives were clean and you are sure no hametz was around and might have mixed in.

More than that

if before Pesach food was cooked (or remained soaking for 24 hours) in a hametz utensil that was not a ben yomo [wasn't used for 24 hours], the food may even be eaten on Pesach, see Mishna Brura 447:39 (quoted from footnote 4 to Artscroll's Kitzur Shulchan Aruch 112:2).

The reason is that, as you write, taste doesn't transfer if the utensils are cold and clean. In addition, hametz that might be absorbed in the dishes is annulled in sixty times its volume before Pesach (but not during Pesach).

Regarding the sauerkraut, there is indeed a rule of kavush k'mevushal (soaking is like cooking) but if the cabbage is clear of hamets and with the rule above, it can still be eaten during Pesach.

Now whether or not you can rely on this ruling in practice, either before the fact or after the fact, depends on what your rabbi will tell you. In modern days, when getting Pesach dishes is so easy and cheap, there is less need to rely on leniencies and "risky practices".

PS. As always things get complicated when cutting onions or other davar charif so the above might not apply directly in this case.