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The primary enemy of crisp-tender vegetables is overcrowding. Vegetables consist predominantly of water: zucchini registers roughly 94% water, broccoli 89%, and carrots 88%. As raw cut vegetables absorb heat, that volume expands outward as vapor.

If you pile diced roots or florets tightly across a tray, that escaping vapor cannot disperse. It gathers in dense pockets, boiling the vegetables in collective humidity. Preventing soggy vegetables requires maintaining at least a 0.5-inch border of bare metal around every cut piece. Use two separate trays rather than cramming everything onto one.

Pan composition matters as much as spacing. A heavy-gauge aluminum baking sheet conducts heat swiftly across its surface, creating immediate bottom contact sizzle. Insulated pans or thin steel cookie sheets distribute heat sluggishly, sweating out moisture before caramelization begins.

Toss vegetables in enough oil to form a thin, glossy sheen. Excess oil deep-fries the food and causes greasiness, while too little leaves dry surfaces that scorch rather than brown. Lay cut edges flat against the metal: that direct contact zone develops rich browning while the upper floret or stem holds its texture.