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Experiment: What is Viscosity? Learn the Definition of Viscosity!

viscosity

What is Viscosity and why is it important in Baking? Do this experiment with Guar Gum and learn how it reacts with acids

What exactly is viscosity, anyway? You are probably wondering this. Well, viscosity, which sounds like vis-cos-it-ee when you say it, is pretty much all about the thick and thin of liquids. If you suffer from food allergies or you know someone who does, you will like this experiment. It teaches about the properties of guar gum, a very important ingredient for commercial baking, and especially people who have to avoid a protein known as gluten.  So read on!

Do you remember the definition I gave you in the Unit 4 Reading "The Science of Gluten-free Cake Baking" from our cooking club curriculum? Well, in case you weren't paying any attention, I'll repeat myself!

Viscosity is a way to measure how well an ingredient resists flow. In other words, it tells us how fast or slow the ingredient actually flows. Got it, now?

molassesviscocityAn ingredient that flows easily like water has low viscosity. You pour it and it moves fast! What about ketchup? Ketchup takes longer to flow out of the bottle so it has a higher viscosity. Now think about honey or molasses. Have you ever heard the saying, "You are as slow as molasses"? Do you think honey or molasses has higher or lower viscosity than ketchup, and why?

That's right! it will probably take honey longer to flow out than it does ketchup.

Now, what about the viscosity of guar gum?

Take a look at the picture at the top of the page. That is guar gum with water added to it. Looks pretty thick, right? Like toothpaste!  In this experiment we are going to test what vinegar does to guar gum. 

I bet you are also wondering, how do we know which is the right amount of guar gum to add to a recipe? Ha! I will tell you from personal experience NOT A LOT! As you can see from this picture, a 1/4 teaspoon of guar gum is pretty thick! Wouldn't you say it has a high viscosity? Yes it does! But what if we add vinegar?  What happens to the viscosity in guar gum? How much guar gum is just right to make the perfect gluten free cake? Hm, you guys have a lot of questions, why don't we put on our science caps and find out the facts!

This is what you need to get started on our experiment:

Our Viscosity Experiment will need special equipment:

Psst!It takes about a minute for the guar gum to set up. You will see it get thicker as time goes on and it absorbs the water.

  • One 4 oz glass
  • a fork or spoon for stirring
  • a paper or styrofoam cup with a hole in the bottom of it (Attn Facilitators: the smaller the hole the longer the experiment takes) You can also use a funnel like the one pictured if you have one handy.
  • a shallow bowl (a ramekin dish or tea cup will probably work fine)
  • A stopwatch timer
  • 1/4 cup of water
  • 1/2 teaspoon of Guar Gum
  • 1 Tablespoon vinegar
  • pencils for recording the information

Viscosity Experiment Directions:

Psst!How long did it take? Did the guar gum have less viscosity when you added the vinegar?

  • Pour 1/4 cup of water into the 4 oz glass.
  • Now pour it through the hole while timing how long it takes for all the water to flow out.
  • Measure 1/2 teaspoon of Guar Gum and pour it into the glass.
  • Stir with a fork or spoon until the powder is dissolved.
  • Now watch for a few seconds as the liquid gells up and sets. Talk about how high the viscosity is.
  • Attempt to pour it out. It will probably be too thick to measure, as it would take all day to move through that little hole.
  • Talk about this with the group.
  • Next, ask a member to measure 1 tablespoon of apple cider vinegar and pour it into the glass.
  • Have another student stir the glass again. Discuss what happens when you add vinegar. Now pour your liquid through the hole.
  • Be sure to have someone time it while you do this.

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