In our unit on pressure, we used plants as a model system. What makes lettuce crispy? How do you revive wilted lettuce? It's really all about pressure- turgor pressure, to be exact.
We prepared tasting samples of dehydrated grapes (aka raisins) and kale chips to demonstrate the vital role that water and pressure play in plants. Under normal conditions, grapes are juicy and firm, and kale is hardy and stiff. We placed both in a dehydrator, which works as a low-temperature oven (~130 °F/54 °C). Water evaporates, and the cells lose turgor pressure and shrink. The grape becomes soft and mushy on the inside, and the kale, which is normally so tough and sturdy, shatters like a chip.
And for reviving that wilted lettuce? Soak it in cold water, of course.
Grapes Boiling water Dehydrator
1) Wash grapes well. 2) Bring a pot of water to a boil. Blanch* grapes in boiling water for 30-60 s. 3) Pat grapes dry. 4) Places grapes on dehydrator racks. Turn on dehydrator. If it has a temperature setting, some recipes suggest 140 °F. Our dehydrator has only one temperature setting of ~130 °F, so we just went by touch. A wrinkled grape with a still-moist center takes 3-4 hours.
*Blanching dissolves the waxy cuticle on the surface of grapes. The wax is a natural defense mechanism against water evaporation.
Kale Olive oil Salt Pepper Paprika, cumin, other seasonings
1) Rinse and dry kale leaves. Cut lengthwise in half, and again in thirds. 2) Toss kale with olive oil in bowl. Sprinkle with salt, pepper, and other seasons. 3) Arrange leaves in single layer on dehydrator racks. Turn dehydrator on. Let run for ~2 hours.