Cooking Class

Ensuring Tender Apples

Why do apples that go straight into the cake batter bake up too firm, while those same raw apples come out soft and tender if microwaved a bit before heading into the oven? Common sense might suggest that precooking simply hastens the fruit’s breakdown. But there’s more to the answer than that. As so often happens in cooking, an enzyme is involved, in this case a temperature-­sensitive enzyme called pectin methylesterase (PME). As the batter’s temperature climbs and lingers between 120 and 160 degrees, the PME sets the pectin in the fruit, so the slices will remain ­relatively firm no matter how long they are cooked. The catch, though, is that the PME is deactivated at temperatures above 160 degrees. Enter the microwave. A three-minute zap quickly brings the apples to 180 degrees—high enough to permanently kill any activity of the PME—so the precooked fruit emerges fully soft in the finished cake.

We even double-checked the science with a side test: heating vacuum-sealed batches of both raw and microwaved apples in a sous vide machine to the final temperature of the cake (208 degrees) for the same amount of time it bakes (1¼ hours). The microwaved apples were predictably tender, while the slices that we didn’t microwave remained firm. Furthermore, these slices never fully softened, even after we continued to cook them for another 40 minutes.

Cooking Class

Batter Up: It's a Two-for-One

To produce this cake’s distinct layers, we started with a simple base batter and, with key additions, made it work in two ways.

CAKE: Adding extra flour to 1 cup of the base batter created a tender, airy top.

CUSTARD: Adding two extra yolks to the rest of the base batter created a creamy, dense bottom.