What binds oil and vinegar?

Activity Type:

If you’ve ever attempted to make salad dressing from scratch, you know that getting the oil and vinegar to mix properly is one of the biggest challenges. Oil and vinegar separate no matter how hard you shake, stir, or whisk them together. This occurs because the molecules that make up vinegar and oil are very dissimilar and attract one another.

Depending on the type of vinegar you are using, acetic acid and water are also typically combined with other acids and alcohols to form vinegars. Polar molecules are those that have a slightly negative charge at one end, or pole, and a slightly positive charge at another end. Examples of polar molecules include water, acetic acid, and alcohol. One or more electronegative atoms in the molecule pull negatively charged electrons toward them, leading to an uneven distribution of charge within the molecule and the development of these slightly charged poles. Because their slightly negative poles have an affinity for their slightly positive poles, polar molecules are typically drawn to other polar molecules. Hydrophilic, which literally translates to “water loving,” refers to polar molecules that are drawn to the polarity of water molecules. ”.

Oils are a different story. Oils are a type of fat (like butter, shortening, and lard) and are considered non-polar. Fats and oils are composed primarily of long molecules called fatty acids (usually bound together by glycerol molecules into groups of three called triglycerides). Most of the atoms in a fatty acid molecule share electrons evenly and are neither negatively nor positively charged (although fatty acids do contain small regions of polarity—just not enough to make the whole molecule polar.) Non-polar molecules love other non-polar molecules and will glom together when mixed with water. You can observe this phenomenon by placing a few drops of oil on the surface of a bowl of water—eventually the drops will form a single large oil slick. Oils repel polar molecules such as those found in vinegar. Because oils also repel water, they are called hydrophobic, which means “water-fearing.”

We need an emulsifier to combine polar and non-polar molecules to create something delicious like mayonnaise, which is essentially a mixture of water and oil. Emulsifiers are the hand-holders of the molecule world. They can simultaneously attract and “hold hands” with both polar and non-polar molecules due to the presence of both hydrophobic and hydrophilic regions in them. This results in the formation of an emulsion, a particular kind of mixture. For instance, separation of the oil from the vinegar will take much longer or not happen at all after thoroughly mixing oil and vinegar with an efficient emulsifier.

You will test a few everyday items to see which one works best as an emulsifier in salad dressing in this experiment, and the results are edible!

a minimum of three of the emulsifiers listed below: honey, dry mustard, garlic paste, tomato paste, and

Whisk, spoon, or other stirring implement

Four small, clear-sided glasses, bowls, or jars: one for the control and three more for the four emulsifiers that will be put to the test.

Please be aware of the following even though the supplies used in this activity are frequently found in home kitchens:

The dry mustard and vinegar used in this activity can cause respiratory irritation if inhaled. Avoid swallowing, shaking, inhaling, or sniffing these products during the activity.

Glass can pose a risk. Clear plastic vials or cups will work for this activity, but they will be much harder to clean and reuse.

Unfortunately, if you work in a space or with equipment where non-food safe materials are handled (such as a laboratory), you should not taste your results.

It might be helpful to premeasure individual portions for each student or group in a class or assign a measuring spoon to each of the emulsifiers. You might want to adapt this process to use volumes that are suitable for your particular lab equipment. For use in a lab setting with test tubes, pipettes, and a scale, print the lab protocol and materials list.

In a clean kitchen space used only for food safe materials, set out four small, clean glasses with clear sides on a stable work area.

To each of three glasses, add ½ tsp of an emulsifier to be tested, putting a different emulsifier in each glass. Label each glass with the emulsifier that was added, and label the empty glass “control.” Label the data sheet with the emulsifiers you will be testing. Unseparated (left) and separated (right) mixtures of olive oil and balsamic vinegar.

To each glass, add four tablespoons of vinegar, and swirl to fully mix in the emulsifier.

To each glass, add four tablespoons of oil. Take a moment to observe the layers of oil and vinegar as they avoid mixing with one another. This is what separation looks like, a process you’ll need to be familiar with in order to collect data in the next step.

Using a fork or a whisk, vigorously stir, whisk, or whip the oil and vinegar in the “control” glass for 30 seconds (time it with a clock or stopwatch). At the end of 30 seconds, start the stopwatch and watch the sides of the glass for 1-5 minutes for signs of separation. When you see that most of the oil has separated from the vinegar, stop the stopwatch and record how long the process took on your data sheet.

Repeat step 5 for each of the glasses containing an emulsifier, rinsing off and drying the whisk after each mixing. If an emulsion has not separated after 5 minutes, write “over five minutes” and the time of day on your data sheet.

After you have mixed and observed all of the emulsifier combinations, go back and check to see if any of the emulsions that didn’t separate earlier have now separated. Record your observations on your data sheet in the column marked “separation time.”

You can repeat steps 1-6 to try out other herbs or spices, such as salt and pepper, to see how they effect the separation time of your dressings. You can also experiment with other vinegars or oils to see how their separation times differ, or investigate the effect of temperature on separation time. When you are done, grab a carrot or piece of lettuce and give your emulsions a taste! [Refer to safety precautions described above.]

Did the mixtures with the emulsifiers take more or less time to separate than your control? Is this what you expected?

Based on your observations of separation time, which emulsifier would you recommend using for making salad dressing?

How would you expect the separation time to change if you added more emulsifier? Why? What about if you added more oil than water?

Lemon juice is mostly citric acid and water. Would you expect it to mix better with olive oil or vinegar? Why or why not?

Look for recipes for other salad dressings or vinaigrettes online. For each, try to identify which ingredient is the polar molecule (hydrophilic), which ingredient is the non-polar molecule (hydrophobic), and which ingredient is the emulsifier.

To learn more about how food science can assist you in creating your favorite condiments, read Ali Bouzari’s SciFri article “Secrets of the Sauce” and listen to our interview with him (excerpt below). You can also print the article for classroom use.

NGSS DCI PS1-A: Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.

NGSS MS-PS1-1: Develop models to describe the atomic composition of simple molecules and extended structures.

NGSS HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

Ariel Zych is Science Friday’s director of audience. She is a retired teacher and scientist who enjoys cooking, observing insects, and being outside in her free time.

Try your hand at being an experimental chocolatier by analyzing the effects of various melting and cooling techniques on the luster, firmness, and texture of finished chocolate.

Perfect for dressing, dipping and marinating. Plus, it’s made from scratch!

One of the most useful items in a cook’s kitchen is a basic vinaigrette (say it with me, vi-ni-gret, not vinegar-et). Although they make for an easy, flavorful salad dressing, they are also useful for marinating meat and vegetables before grilling or roasting. Additionally, once you master the fundamental vinaigrette formula, you have access to countless flavor combinations that don’t call for a specific recipe. So let’s get started and learn how to make a simple vinaigrette. For the video guide, click here.

Watch on your Android, Apple TV, Fire TV, iPhone, iPad, or Apple TV.

Really, all you need to make a vinaigrette are four ingredients: oil, vinegar, an emulsifier, and flavorings. Simple oil and vinegar in a 3-to-1 ratio make up a vinaigrette’s body. By using this special ratio, the dressing is given body and a smooth texture without becoming overly sour or acidic. You also need an emulsifier to keep the oil and vinegar suspended in a gorgeously even mixture. Emulsifiers work as a glue to prevent your vinaigrette from separating by mixing easily with both oil and water. Dijon mustard, honey, egg yolks, tomato paste, and even roasted garlic are frequently used as emulsifiers in vinaigrettes (some are better emulsifiers than others). Last but not least, adding herbs, salt, and pepper will give your vinaigrette a lot of flavor.

2 Mix your emulsifier and herbs

Start by combining the emulsifier with the herbs and spices of your choice before constructing the vinaigrette. I always add a minced clove of garlic to my vinaigrette because I like it to have a particularly strong flavor. If you want a flavor that is slightly garlicky but not overpowering, minced shallot is fantastic. Keep it simple with a simple blend of herbs, pepper, and salt for an extra-mild vinaigrette. A clove of minced garlic, some freshly cracked pepper, 1/2 tsp. dried oregano, and 1/2 tbsp. Dijon mustard serve as emulsifiers in my go-to vinaigrette. I add salt to taste once the vinaigrette is mixed.

Next comes the vinegar. Here is where you can significantly alter the vinaigrette’s character. Red wine vinegar has a strong, tangy flavor that I love, but you can also use other acidic liquids, such as citrus juice, or sweet balsamic vinegar, mild champagne vinegar, or sherry vinegar.

Mix the herbs and emulsifier with two tablespoons of vinegar (or another acidic liquid). These ingredients should be thoroughly combined before being used to create an emulsion with the oil.

Choose a neutral oil for your vinaigrette, such as canola, safflower, sesame, or grape seed oil. These oils are frequently referred to as “salad oils” because of their mild, undetectable flavor. Use extra-virgin olive oil, walnut oil, or toasted sesame oil in combination with salad oil for a more flavorful dish. You’ll need a total of 6 tablespoons of oil to achieve a 3-to-1 ratio of oil to vinegar. The outcome will depend on how you combine the oil and vinaigrette. Traditionally, the vinaigrette is vigorously whisked while the oil is gradually added in a thin stream. With the aid of the emulsifier, this disperses the oil into tiny droplets that are then readily suspended in the vinegar. Even though it only takes a few minutes, this process requires a lot of effort.

How To Prepare Oil And Vinegar Dressing