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Vinaigrette

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Ingredients to make Greek salad dressing. Photo credit: Julle Magro (magro-family/Flickr)

Homemade vinaigrettes are about as easy as they look: mix oil, vinegar, and spices; shake before pouring. For those who want vinaigrettes without the inelegant step of shaking before serving, the solution is simple; add an emulsifier.

Understanding the role of an emulsifier first requires some familiarity with the primary components in vinaigrette, vinegar and oil. Vinegar is composed of acetic acid and water, which are polar compounds. In a polar molecule, one or a group of atoms have a stronger pull on the electrons in the molecule. Due to this uneven share of electrons between the atoms, weak charges form on opposite ends of the molecule [Figure 1a]. The weakly positive and negative charges on the polar molecule are called dipoles. Oil, on the other hand, is a type of lipid, which is a nonpolar compound. Since the atoms within the lipid are largely identical, the electrons are evenly distributed across the lipid molecule [Figure 1b]. Therefore, nonpolar molecules do not have such well-developed dipoles.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

Figure 1. a) Acetic acid and water are polar molecules. b) Lipids are nonpolar molecules.

In solutions, compounds follow the chemistry fiat, like dissolves like. Polar molecules only interact with other polar molecules. Likewise, nonpolar molecules prefer to be surrounded by other nonpolar molecules. When a polar solution, like vinegar, is vigorously mixed with a nonpolar solution, like oil, the two initially form an emulsion, a mixture of polar and nonpolar compounds. However, this emulsion is unstable and will very quickly form layers in what’s known as phase separation. The solutions separate into layers according to their respective densities due to an aversion to each other. (In this case, because oil has a lower density than vinegar, it happens to be the layer floating on top.)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

Phase separation in vinaigrette. Photo credit: Jan Persiel (janpersiel/Flickr)

To prevent phase separation, an emulsifier can be added to the vinaigrette to stabilize the emulsion. Emulsifiers are amphipathic compounds, meaning the molecule has both a polar and nonpolar section [Figure 2]. Common food emulsifiers include egg yolk, soy lecithin, garlic, and mustard. Egg yolk contains the emulsifying agent lecithin. The vegan version is isolated from soy and is thus known as soy lecithin. Lecithin is a commonly used emulsifier in many other food products, such as chocolates, mayonnaise, and Hollandaise sauce. Amphipathic compounds found in garlic include diallyl sulfide, allyl methyl disulfide, and diallyl trisulfide [1]. Mustard, the condiment, is made from mustard seeds. Emulsifying agents in the condiment, such as the pectin rhamnogalacturonan, originate from the mucilage of mustard seeds, a thick, glutinous layer that surrounds the seed hull [2,3].

Figure 2. a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

a) Lecithin is an example of an emulsifying agent. b) Emulsifying agents stabilize emulsions by interacting with both the polar and nonpolar compounds. (b) adapted from Ioana.Blog.

So with a helping hand from emulsifiers, homemade vinaigrettes can still be as simple yet elegant as they seem, and best of all, ready to serve whenever.

Greek Salad Vinaigrette (Recipe from Ina Garten’s Barefoot Contessa)

½ cup olive oil
¼ cup red wine vinegar
2 cloves garlic, minced
½ tsp Dijon mustard
½ tsp ground black pepper
1 tsp salt
1 tsp dried oregano

  1. In a bowl, whisk together the vinegar, garlic, mustard, salt, pepper, and oregano until well mixed.
  2. While still whisking, slowly add the olive oil.
  3. When a stable emulsion forms, serve with salad or store in a covered bowl or bottle.

References cited

  1. Kimbaris, A.C., Siatis, N.G., Pappas, C.S., Tarantilis, P.A., Daferera, D.J., Polissiou, M.G. Quantitative analysis of garlic (Allium sativum) oil unsaturated acyclic components using FT-Raman spectroscopy. Food Chemistry, 2006; 94: 287-295.
  2. Cui, W., Eskin, M.N., Biliaderis, C.G., Marat, K. NMR characterization of a 4-O-beta-D-glucuronic acid-containing rhamnogalacturonan from yellow mustard (Sinapis alba L.) mucilage. Carbohydrate Research, 1996; 292(1): 173-183.
  3. Leroux, J., Langendorff, V., Schick, G., Vaishnav, V., Mazoyer, J. Emulsion stabilizing properties of pectin. Food Hydrocolloids, 2003; 17: 455-462.

Alice PhungAbout the author: Alice Phung once had her sights set on an English degree, but eventually switched over to chemistry and hasn’t looked back since.

Read more by Alice Phung


Vinny Dotolo

Vinny Dotolo is one half of the culinary duo dubbed as “Kings of Dude Food”. Alongside John Shook, the pair opened Animal, a meat-centric restaurant located in L.A.’s Fairfax Village. Following the success of Animal, the duo have since opened the equally acclaimed Son of a GunTrois Mec, and Petit Trois.

Vinny Dotolo

What hooked you on cooking?
Mainly the kitchen culture and obviously the delicious food and the never-ending learning process.
The coolest example of science in your food?
I guess science happens every day in our kitchens. Looking at it from a scientific perspective, I think the transformation and cooking of proteins.
The food you find most fascinating?
Eggs have always kept my mind racing.
What scientific concept–food related or otherwise–do you find most fascinating?
Emulsifications.
Your best example of a food that is better because of science?
Fermented foods.
How do you think science will impact your world of food in the next 5 years?
In general, I think understanding food and how and why things happen in the kitchen. Different techniques seem to be popping up constantly.
One kitchen tool you could not live without?
Vita prep.
Five things most likely to be found in your fridge?
Pickles
Cheese
Lemonade
Jam of some kind
The baby’s food
Your all-time favorite ingredient? Favorite cookbook?
Lemons are my favorite ingredient, they brighten everything up! Favorite cook book is tough. I have such a diverse collection but the one that changed my life and perspective and appreciation for food is the French Laundry.
Your standard breakfast?
Toast and coffee.