Key concepts
Fat
Nutrition
Food
Snacks

Introduction
Do you enjoy eating potato chips? If you do, you are not alone. Potato chips are a very popular snack food. In fact, many people eat the equivalent of more than one bag of chips per month. When eating potato chips, have you ever noticed that your hands get greasy? Maybe you have heard people explaining that potato chips are bad for you because they contain too much fat—some of it unhealthful. Is this true? Try this activity and find out—by spotting the fats in potato chips!

Background
Fats are actually a main component of our diet and are important for our bodies to work. A healthy diet consists of about 20 percent of calories from fat. Why is fat useful to us? Our body uses fat for storing energy and for digesting essential fat-soluble vitamins. Our brain also needs fats to function well. So why do we hear all these stories about bad fats? The reason is that there are different types of fats in foods and not all of them are healthy.

If you have ever looked at nutrition labels of foods, you might have noticed that the fat category is subdivided into “saturated,” “unsaturated” and (sometimes) “trans” fats. The different names represent the various types of fats that result from each kind of fat molecule’s chemical structure. But which of these are “bad” and which are “good” fats? Unsaturated fats—mostly found in plant-based foods and oils—have been shown to be beneficial to your health. Saturated fats—which mainly come from animal sources—have been associated with an increased risk of cardiovascular diseases. “Trans fats,” in particular, which are artificially processed, should be avoided in a healthy diet.

Most food we eat has some amount of fat in it, often in an invisible form so we do not even notice it. But did you know that potato chips contain up to 35 percent fat? Some of this fat is greasy, meaning it is partly melted and leaves a film on many things it touches. Because of this, an easy way to make these fats visible is the so-called grease spot test. Grab some chips and see for yourself in this activity!

Materials

  • Clean working area that can get greasy
  • Graph paper
  • Wax paper
  • Two sheets of regular paper
  • Rolling pin
  • Scissors
  • Timer
  • Digital kitchen scale
  • Two varieties of potato chips (Use regular baked chips and reduced-fat chips. It is best, but not required, if both varieties are the same brand.)
  • Tape
  • Well-lit window (and permission to tape pieces of paper to it)

Preparation

  • With your scissors, carefully cut two pieces of graph paper into rectangles approximately 18 by 12 centimeters (seven by five inches).
  • Cut two slightly larger size pieces of the wax paper.
  • Take one sheet of the regular paper, the cut graph paper and the wax paper and label each one “Regular Chips.” Label the other set of three papers with “Reduced-Fat Chips.”
  • On the kitchen scale, weigh about 28 grams (or one ounce) of each kind of potato chip, the regular and reduced-fat variety. Set each pile aside on your table for now.

Procedure

  • With your hands, take a couple of regular potato chips out of the bag. Look at them closely. Do they look very greasy?
  • Crumble the potato chips with your fingers. How do your fingers look? Can you see some shiny grease on them? How do your fingers feel when you rub them against one another?
  • After washing and thoroughly drying your hands, repeat the first and second steps with the reduced-fat chips. Do they look very different? Are your hands less greasy after you crumble them with your fingers?
  • Clean your hands again and put the sheet of paper labeled “Regular Chips” down on the table. Take the piece of graph paper labeled “Regular Chips” and place it on top of the regular piece of paper.
  • Take the pile of regular chips that you prepared and spread them evenly on the graph paper so the whole area is covered with chips.
  • Place the wax paper labeled “Regular Chips” on top of the chips.
  • Carefully press down on the wax paper and crush the chips. Try to keep the pieces evenly spread out on the graph paper. Use the rolling pin to crush the chips into smaller pieces.
  • Set your timer for one minute, and let the crushed chips sit on the graph paper for the full minute. After the minute has passed, put the wax paper and the potato chips into the trash. Try to remove all of the extra chip bits from the graph paper, too. Do you notice a grease stain on the graph paper? How large is the grease stain?
  • Tape the graph paper to a well-lit window so you can see the stain clearly; let it hang there for about 10 minutes. How much of the graph paper is covered in grease? Are there any areas that are not translucent? What are the sizes of the individual grease stains on the graph paper?
  • Also look at the regular sheet of paper that was underneath the graph paper. Did any of the grease spots leak through the graph paper? How many grease spots do you see on this sheet of paper?
  • Repeat steps 4 through 10 with the reduced-fat chips. How does the grease spot on the graph paper look this time? Is more or less area of the graph paper covered with grease? What do you notice when you compare the sizes of the individual grease spots with the spots left by the regular chips? On the underlying sheet, do you count more or fewer grease spots?
  • Finally, look at the nutrition labels on both bags of potato chips. How much fat is in each of them? Do these numbers agree with your grease spot results?
  • Extra: As you look at the grease spots on the graph paper, try to count all the squares that are covered in grease; this way you also have a quantitative measurement of the fat content in the two different potato chip varieties. Compare the results for both of the chip varieties. Did you expect these results? How many more squares were covered in grease using the regular chips compared with the reduced-fat ones?
  • Extra: Often foods with reduced fats have additional ingredients to take the place of the missing fats. Examine the labels of the two bags of chips. Do you see differences in the ingredient lists? What other differences do you see on the nutritional labels?
  • Extra: What other foods do you think contain a lot of invisible fats? Try to produce grease spots with other foods that you find in your kitchen. Some examples of foods to try are nuts, chocolate, cheese or cereals. Were you surprised about any of your results?
  • Extra: Potato chips are, of course, not the only type of “chip” you can eat as a snack. And many can easily be made at home—using healthier, unsaturated fats. With an adult, look online to find recipes for baked chips made from sweet potatoes, plantains or even kale. Could you make a snack that is healthier than store-bought potato chips? With an adult's help, try out some of your new baked chip recipes!

Observations and results
Did you see some really big grease spots on the graph paper after crushing the chips? This is no surprise—fat is a major ingredient in chips, as you probably noticed when you looked at their nutrition labels. When you just look at the chips, however, you do not necessarily see all the fat they contain. Only when you crumble the chips with your hands do you start to detect these invisible fats as your fingers become very shiny and slippery from all the grease.

When crushing the chips on the graph paper, a big grease spot should have appeared. If you held the paper against a light source, you saw that all the areas covered with grease became translucent. Why is that the case? The reason why fats produce grease spots is that they are nonvolatile, meaning they have a very high boiling point and do not evaporate easily. In contrast to water, fats that get absorbed by paper cannot get enough heat to evaporate at room temperature. An easy way to test this is to take a sheet of paper and put one drop of oil next to a drop of water. At first, both areas look wet and translucent but after awhile the water evaporates and the spot dries whereas the fat spot remains visible. This is because when fat is absorbed into the paper’s pores, the grease-stained part of the paper—which is normally white due to the scattering of light that shines through it—allows less scattering, and the light passes through it, appearing darker in color and translucent.

When you compared the two different potato chip varieties, you probably observed that most of the squares were covered with fat for the regular chips and the underlying sheet of paper might even have had significant grease stains as well. Using the reduced-fat chips, however, should have resulted in a much smaller grease-covered area, both on the graph paper as well as on the sheet underneath. This makes sense because these kinds of chips contain less fat that can be absorbed by the paper.

More to explore
What Is Fat?, from TEDEd
Learning about Fats, from KidsHealth
How Greasy Are Your Potato Chips?, from Science Buddies
Science Activity for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies