Marinades and Dry Rubs: How do they work?

KITCHEN SCIENCE: October 17, 2024

CONCEPTS

Marinades

Adsorption vs Absorption

Acids in the kitchen

TOOLS & SUPPLIES

Tofu, extra-firm

Food dye

Distilled white vinegar

Salt & sugar

Knife

Cutting board or dinner plate

Four cups or bowls, each at least nine ounces in size

Masking tape or painter’s tape and a pen or permanent marker

Tap water

Clean spoons or other utensils for stirring

Measuring cups

Measuring tablespoon

Sheet of white paper

Clear plastic wrap

A fork or a slotted spoon

A timer or clock

The Power of Marinades

In this activity you’ll test how various ingredients affect the adsorption (yes, with a “d”) of a marinade ingredient onto the surface of a food. (The word “adsorb” is used to describe the process by which a substance adheres to the surface of an object, as opposed to being absorbed into it.)

METHOD

  1. Cut the tofu block into eight cubes, where each cube is about one half an inch on each side.

  2. Label four plastic cups as follows: "water," "salt," "vinegar" and "sugar."

  3. To the cup labeled "water" add one cup (C) of water. To the cup labeled "salt" add one tablespoon (Tbsp.) of salt and one C of water. To the cup labeled "vinegar" add one-quarter C of vinegar and three-quarter C of water. To the cup labeled "sugar" add one Tbsp. of sugar and one C of water. How well do you think the different ingredients will stick to the tofu cube's surface?

  4. Add eight drops of food dye to each of the cups. '

  5. Using a clean spoon or other utensil for each cup, stir the solutions so that the dye gets mixed in and the salt and sugar are completely dissolved in their cups.

6. Carefully add two tofu cubes to each of the four cups. Let the tofu cubes marinate in the cups for 45 minutes at room temperature. (Do not worry if the cubes in the salty water float.)

7. While the cubes are marinating, lay a white sheet of paper on a nearby surface and cover it with clear plastic wrap.

8. When the cubes are done marinating, use a fork or slotted spoon to remove the cubes from each cup. Place the cubes on the sheet of paper, leaving the cups that held the cubes nearby so you know which cup each cube came from.

9. Examine the cubes. (If not all of the sides on a cube are equally dyed, examine an averagelooking side on the cube.) Which cubes became the most dyed? Which were the least dyed? How do they compare with the cubes from the cup that only had water and food dye? What does this tell you about how well the different ingredients (sugar, salt and vinegar) stick to the surface of the food?