What makes foams stand up straight

Above: A little soap and water is all it takes to make your own science experiment. Courtesy Junction of Occupational Therapy Function. Douglas Durian, a professor of physics at UCLA suggests the following: "Take some shaving cream and put it in your hand. Touch it. Run your fingers through it.

Ask yourself, is it a solid, a liquid, or a gas? The gas subdivides the liquid into a matrix of tiny bubbles. Good foams usually contain complex molecules that toughen the walls of the bubbles. Milk fat, for instance, serves this purpose in whipped cream. The way the bubbles stick together or slip past one another determines how the foam behaves.

Much of what is known comes from trial and error. No theory currently exists for predicting exactly how stiff or oozy a foam will be based on its traits like the size of its bubbles or the amount of liquid it contains. And the precise stiffness of a foam is crucial for many uses. Just imagine: a fire-retardant foam that must flow quickly through the valve of the extinguisher and then cling tightly where it lands; or a counter-biological weapons agent that expands to fill cracks and crevasses and kills microbes hiding there.

Durian would like to take the guesswork out of foams by learning more about their fundamental physics. Just know that even with the freshest eggs, there is no way to completely eliminate the risk from salmonella in raw eggs and poultry products. Please also remember that the very young, very old, ill, pregnant, and immuno-compromised are more susceptible to food-borne illness than the average healthy adult. Copper bowls are recommended for a variety of reasons.

They were popular for whipping egg whites even as early as the bundle-of-straw whipping days! Copper prevents overbeating by preventing strong sulfur-sulfur bonds from forming between proteins.

The downside is that it introduces extra copper into your food, which some experts think could pose a health risk. Copper bowls are also expensive and difficult to keep clean. Plastic bowls are not recommended because they have porous surfaces that can trap fat particles even after washing.

Yes; plastic bowls can trap fat particles, but will that really hurt your foam? The best option is to use a glass or stainless steel bowl along with a dash of cream of tartar to prevent overbeating. Those that oppose copper bowls on a nutritional basis are taking the safest possible stance. I recommend that route as well why take the risk? You will need to add cream of tartar to prevent overbeating. Cream of tartar a source of tartaric acid is added to egg whites to prevent overbeating.

It works by decreasing the pH of the egg foam and preventing the formation of sulfur-sulfur bonds between proteins, which are responsible for the crumbly, leaky texture of overbeaten foams. Acids, like cream of tartar, flood the egg with excess hydrogens.

This allows egg whites to be beaten for much longer without overbeating. Salt is commonly recommended as a substitute when cream of tartar is unavailable. Salt definitely does NOT work. In fact, salt increases whipping time and decreases foam stability by competing for bonding space along the protein, which weakens the protective protein wall around each bubble. In the photo below, the foam on the left was whipped with cream of tartar.

The foam on the right was whipped with salt. The cream of tartar foam looks fluffy and uniform, with stiff peaks and a fine texture. The salt foam is overbeaten and leaky, with a crumbly-looking texture. If your recipe asks you to whip your egg whites with a pinch of salt, just know they REALLY mean to say cream of tartar instead.

Sugar is delicious and completely changes the texture of egg white foams. Most recipes call for adding sugar only at the end of beating, but the occasional recipe directs you add it from the start. Is it really necessary to wait? Yes; it does make a difference whether you add the sugar at the start or finish of beating. Sugar can both help and hurt egg whites. This leaves you with a syrupy, dense foam. Add it a tablespoon at a time toward the end of whipping and the egg whites have time to incorporate more air before any competing sugar molecules are introduced.

The purpose of the slow addition is to prevent the sharp sugar crystals from popping too many bubbles before they are able to dissolve. And the really great news about sugar foams aka meringues is that the sugar adds structure and stability by thickening the fluid surrounding the bubbles and protecting them from breakage. In fact, it completely prevents the liquid portion of the foam from draining toward the bottom of the bowl, as will happen over time with ALL un-sugared raw egg white foams.

You can leave it out all day and night and not a drop of liquid will leach out. The egg foam on the left was beaten with sugar from the start.

The egg foam on the right had the sugar added slowly only after reaching very soft peaks. Perfect for pies or meringue cookies! Add sugar one tablespoon at a time only after reaching soft peaks. This will give you perfect, stable meringue every time. Adding water to your egg whites thins them out and makes them easier to beat. Not really. Maybe a soft foam is okay with you, but the added water will quickly drain from the bubble walls, leaving you with a fragile, dry foam with a watery layer at the bottom.

To the egg white below, I added a teaspoon of water, which is about as much water as you would introduce by leaving a large bowl wet after a rinse. As you can see in the right hand photo, the water drained out fairly quickly, leaving my foam layer dry and brittle.

Avoid adding water to your egg whites. This is why recipes often tell you to use a clean, dry bowl. Almost every recipe involving egg white foams will require you to recognize soft peaks, stiff peaks, and an overbeaten foam. Knowing which phase your egg foam is in removes most of the confusion cooks have regarding egg foam recipes. A foam becomes stiffer as more air is whipped into the mixture.

The slideshow below shows an un-sugared foam in its different phases. Note that there are a range of soft peaks and a range of stiff peaks. The slideshow below shows a sugared foam meringue in its different phases.

Know your peaks. Its tip can be a little droopy beginning stages of stiff peaks , as long as the base of the peak is firm and able to hold angular shapes. The longer you whip, the smaller the bubbles get and the smoother and more reflective the surface of the foam.

This happens when the egg proteins have bonded so strongly with each other that they squeeze the liquid out from between them, which results in thin, fragile bubble walls and a growing puddle of watery egg liquid at the bottom of the bowl.

If you overbeat your foam, you may need to start over. Plain eggs whites move quickly from soft peaks to overbeaten, so keep a close eye on them! Adding cream of tartar at the beginning will help prevent you from overbeating your eggs, and it really makes a world of difference see number 4. If you added sugar to your foam, your overall foam will be heavier, stickier, and with finer, smaller bubbles and a shinier surface, and most importantly, it will be more forgiving.

Another consideration with sugary foams is grit. I tried, and the motor on my mixer overheated long before anything bad happened. Fats and detergents soaps destroy foams. Even if you get them whipped, a few drops of fat will continually work to degrade your foam. Detergents can be just as damaging. In fact, they both work to destroy egg white foams in much the same way.

Soon, the protein-protein bonds that made a protective wall around each bubble are weakened, and the bubble pops. The fat or detergent molecules move on to find the next bubble to cozy up to…and destroy. You get the idea. The most common method of fat contamination is from egg yolk. If you allow some yolk, oil, butter, chocolate, soap or detergent to co-mingle with your egg whites even in trace amounts! Haha, if you have to ask…well, you can check the symptoms on WebMD yourself.

Recipes for mousses and cocktails often call for raw egg whites, but luckily there are several safe alternatives to choose from. Pasteurized liquid egg whites are available in a carton and are as safe and shelf stable as milk. Powdered egg whites can be kept at room temperature and last quite a long time.

The simple act of cracking an egg can transfer bacteria from the shell into the inside of the egg. Pasteurized egg products have been treated with enough heat to kill harmful bacteria like salmonella. The heat of that process also denatures some of the proteins in the egg, which changes the appearance and whipping properties somewhat. On the left in the photo below is a foam whipped from pasteurized carton eggs.

On the right is a regular raw egg. As you can see, the carton egg foam is a bit softer and coarser in texture. However, their volumes are very similar, and both were able to reach stiff peaks. The best alternative in my experience : pasteurized egg whites from the carton. Physical Science. Earth and Environmental Science. Behavioral and Social Science.

See the Materials and Equipment list for details. Wash your hands after handling raw eggs. You should not eat any of the foams you make in your experiment. Share your story with Science Buddies! Yes, I Did This Project! Please log in or create a free account to let us know how things went.

Science Buddies Staff. Accessed 12 Nov. Introduction A scoop of vanilla ice cream in a tall glass. Bibliography These sources discuss what forms are and how they can be formed and stabilized: McGee, Harold. On Food and Cooking. New York, NY: Scribner, Barry, P. The Strange Physics of Foam. Retrieved May 20, This source describes what emulsifiers, like the lecithin in egg yolk, do: Wikipedia Contributors. Wikipedia: The Free Encyclopedia. Retrieved May 15, Note: A computerized matching algorithm suggests the above articles.

It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results! Learn more about the News Feed. Test tube rack; available at Home Science Tools. Impact safety goggles; available at Home Science Tools. Experimental Procedure Note: Because the test tubes used in this experiment are not "food-grade" designed for food preparation , and because raw eggs are not safe to eat, you should not eat any of the foams you make in your experiment.

Preparing for Testing Create a data table for each of your test liquids: Tap water This will serve as your negative control, meaning it will produce a negative result and will not make a foam. Nonfat Milk Data Table Time min Trial 1: Distance from the starting level to the top of the liquid cm Trial 2: Distance from the starting level to the top of the liquid cm Trial 3: Distance from the starting level to the top of the liquid cm Average distance from the starting level to the top of the liquid cm Trial 1: Distance from the top of the foam to the starting level cm Trials 2: Distance from the top of the foam to the starting level cm Trial 3: Distance from the top of the foam to the starting level cm Average distance from the top of the foam to the starting level cm 0 3 6 9 12 15 20 Food Scientist or Technologist.

Log in to add favorite More Menu Read More. Food Science Technician. Variations Using instant, nonfat, dry milk powder and tap water, investigate how changing the amount of milk protein affects the time it takes for the foam to collapse. Investigate what happens when you create a foam and then leave it exposed to the air and evaporation remove the rubber stopper. How does this change the rate at which the foam collapses? Investigate if the rate of foam collapse is dependent upon how much foam surface area is exposed to the atmosphere.

See if temperature affects foam volume or longevity. Experiment with other emulsifiers, like honey and dry yellow mustard. Try combining ingredients to see if foam volume or longevity is improved. Add fat, like cooking oil, to a test liquid to see how that impacts foam volume or longevity. Focus on egg whites and investigate how salt, water, sugar, egg yolk, fat, temperature, and egg age affect the foam volume and longevity.