Summary
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Abstract
Brrrr, freezing cold! It's the worst nightmare of any fresh fruit or vegetable! If the produce in your kitchen had legs, they would run in a panic every time the freezer door opens. Why? Well, freezing temperatures are not kind to fresh produce. Freezing kills the plant tissues and alters them on both a chemical and physical level. Chemically, the enzymes in the produce become more concentrated and do not work normally, so that discoloration, off-flavors, vitamin breakdown, and toughness may develop. Physically, the water inside the cells of the fruits and vegetables crystallizes and expands as it freezes. The cell walls become cut and damaged by the sharp crystals, so that when the produce thaws, the water leaks out, and the produce becomes floppy and limp.Manufacturers of frozen produce try to get around these problems in two ways:
- They utilize a technique called blanching to inactivate the enzymes that cause problems.
- They freeze the produce very quickly and to very low temperatures (-40°F). This minimizes the size of the ice crystals; thus, less damage is done to the cell walls.
In this cooking and food science fair project, you will investigate the power of blanching to improve the quality of frozen vegetables. You will peel and chop a vegetable into equally sized pieces, and then divide it into two groups. One group will undergo blanching, where it will be immersed for 1-2 min in rapidly boiling water, and then immediately scooped up and plunged into an ice water bath to stop the cooking. After the blanching, the vegetable will be drained and frozen in a single layer as rapidly as possible. The other group will not undergo the blanching process, but will simply be frozen in a single layer. Compare the color, texture, and toughness of the two groups after they are frozen solid for a week and a half and then thawed. A testing method for toughness is given in the Science Buddies science fair project, Tough Beans: Which Cooking Liquids Slow Softening the Most?. You can also select a sample piece of vegetable from each group, cut a cross-sectional slice, and examine it using a magnifying glass. Note any structural differences that you see.
Bibliography
- McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004. pp. 18-19, 24, 146-147, 206, 277-278, 495-496.
This source describes the process of blanching:
- W Contributors. (2008, May 22). Cookbook: Blanching. Wikibooks. Retrieved October 9, 2008.
This source describes how to prepare different types of vegetables for freezing:
- Heller, K., Bond, J.M. (1996, July). Freezing Vegetables. North Dakota State University Agriculture and University Extension. Retrieved October 9, 2008.
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Variations
- If you have a freezer capable of "deep-freeze" temperatures, evaluate the physical properties and ice crystal sizes that are produced when blanched produce is quickly frozen at the lowest freezer temperature possible, against the physical properties and ice crystal sizes that are produced when blanched produce is frozen at 0°C (the freezing point of water).
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