What’s the secret to making this bread moist? It’s none other than zucchini! (And no, you can’t even taste it!)
Adjust oven rack to middle position and heat oven to 325 degrees. Spray inside bottom and sides of 8½-by-4½-inch metal loaf pan with vegetable oil spray.
In medium bowl, whisk together whole-wheat flour, all-purpose flour, salt, cinnamon, baking powder, baking soda, and nutmeg.
In large bowl, whisk together brown sugar, eggs, oil, and vanilla.
Use chef’s knife to trim off ends of zucchini. Shred zucchini on large holes of box grater and squeeze dry in dish towel (following photos, below). Transfer zucchini to bowl with brown sugar mixture. Use rubber spatula to stir until combined.
Add flour mixture and use rubber spatula to gently stir until just combined and no dry flour is visible. Do not overmix (see Food for Thought, below).
Place loaf pan in oven. Bake until zucchini bread is golden brown and toothpick inserted in center comes out clean, 1 hour and 5 minutes to 1¼ hours.
Use oven mitts to remove loaf pan from oven (ask an adult for help). Place loaf pan on cooling rack and let zucchini bread cool in pan for 15 minutes.
In this bread, zucchini tastes sweet and mild thanks to its costars cinnamon, nutmeg, brown sugar, and vanilla. The zucchini actually adds something very important to this bread: moisture! (After all, zucchini is about 95 percent water.) But there’s a thin line between too little and too much moisture. (No one likes heavy, soggy zucchini bread.) This is why we squeeze out the extra water before adding the shredded zucchini to the batter.
To keep muffins, scones, and quick breads as light and tender as possible, the key is to not overmix the batter. This means mixing until just combined and the batter is not completely smooth. Why? The more you mix, the more the proteins in the flour combine to form gluten. The more gluten, the more structure and the tougher the quick bread. To prevent tough and squat breads, keep mixing to a minimum!