Issur to Degrade Food
25. Besides for the issur of bal tashchis, there is an issur to ruin or spoil food in a degrading, scornful manner (רמב"ם פ"ז ברכות ה"ט ). This issur is derabonon and applies even in cases where there is no issue of bal tashchis. The reason for this issur is because it gives the appearance that one rejects Hashem’s gifts (רש"י תענית כ: ).
Food That Is Not Yet Edible
26. Most poskim hold there is only an issur to degrade food that is already edible. If it still needs to be cooked or baked before becoming edible, it is not considered food for the purposes of this issur (מס' סופרים הי"ד הובא בב"י סוף סי' קע"א, שו"ת הלל אומר או"ח סי' קי"ח).
27. Throwing wheat kernels at a chosson. This is the basis to be meikel for the minhag to throw wheat kernels at a chosson on the way to the chuppoh even though they will be stepped on (שעה"צ סי' קע"א סק"כ ). Still, some are machmir to only throw them in a clean place and to sweep them up afterward (שו"ע שם ס"ה ).
28. The old practice in Yerushalayim to stick posters onto walls by the streets with a mixture of flour and eggs as glue did not transgress the issur of degrading food, since such a mixture is inedible to most people.
For Healing Purposes
29. One may use food for a purpose other than eating or regular usage if it is for healing reasons. Any way food is used in healing is not considered degrading or wasteful (תשב"ץ הובא בס' ברכת השם סי' ג' הע' ל"ח ).
30. Treating pinworms in the body. Thus, one may put bread crusts in hot vinegar and then place them on the navel for a few minutes to treat pinworms (הגרי"י פישר ), even though this will cause the bread to become disgusting (ע"פ הגמ' יבמות ע"ו. ).
