Moisture Content
Moisture content is how much water is trapped inside a food or material.
A dry sponge is a stiff block with no water inside it. A wet sponge holds tiny drops of water trapped in all its small holes. The more water fills those holes, the heavier and softer the sponge feels. Moisture content measures how much of that space inside is filled with water.
Explaining moisture content by grade level
An orange is heavy because it holds a lot of water inside. You can find out how much by weighing it before and after it dries out. The water part is the moisture content. Most fruits have more water in them than you might guess.
Projects that explore moisture content
This experiment tests how moisture content shapes popcorn results by adjusting it in two directions. Soaking kernels in water for an hour adds moisture. Drying them in an oven removes it. You then pop each batch in a hot-air popper and count the unpopped kernels to see how the water inside each kernel affects whether it pops.
Fruits hold a surprising amount of water, and drying an orange reveals exactly how much. You weigh a whole orange, slice it thin, spread the slices on foil, and let a desk lamp and fan drive off the moisture through evaporation. When the slices are completely dry, you weigh them again. In this experiment the orange lost about 81 percent of its weight, and nearly all of that came from the water trapped inside.
You dry blocks of redwood, teak, black oak, and red maple in an oven and measure how much each one shrinks. Different types of wood hold different amounts of moisture, so they shrink by different amounts.