Pouring boiling water on mustard powder destroys its heat, leaving it bitter and bland.

The characteristic heat of mustard is not present in the dry seeds but is the result of a chemical defense mechanism. When mustard seeds are crushed and hydrated, the enzyme myrosinase reacts with glucosinolates like sinigrin to produce allyl isothiocyanate. This volatile oil is what creates the pungent, nasal-clearing sensation associated with brown and black mustard varieties.Temperature plays a critical role in this enzymatic reaction. Research indicates that myrosinase begins to denature and lose functionality at temperatures exceeding 140°F (60°C). If boiling water is used, the enzyme is destroyed instantly, preventing the chemical reaction from ever occurring and leaving only the bitter glycosides behind.Culinary experts and food scientists, such as those at the University of California, suggest that the reaction reaches its peak potency after roughly 10 to 15 minutes of hydration at room temperature. Because the resulting isothiocyanates are unstable and dissipate quickly, an acidic stabilizer like vinegar or lemon juice is added to halt the reaction and lock in the flavor. This process is essential in the production of Dijon and English mustards to ensure a consistent level of pungency for consumers.