Parashas Bo · Shemos 12:17 · TT note 4
Torah Temimah on Shemos 12:17, note 4 (on וּשְׁמַרְתֶּם אֶת הַמַּצּוֹת) points to practical guarding rules (Pesachim 48b area).
Sefaria — Exodus 12:17
Sefaria — Torah Temimah on Exodus 12:17
English: “And you shall guard the matzos” — guard it so that you do not bring it to a state of unfitness. Hence they said: if it begins to rise, cool it with cold water; se’or and cracked [dough] — burn.
Practical application of shimur during baking.
Active measures keep dough from becoming chametz; once it reaches se’or or sidduk, it is burned.