Lipids and Emulsifying Agents: Mayonnaise

painted egg

It’s All About Eggs

This egg was hand-painted by Barbara Muth, a friend who is a very talented egg painter. In addition to painting eggs or decorating them in other elaborate ways, we use eggs for many purposes, including eating them, cooking with them in various recipes, using them in scientific research, using them to make a durable paint, and using them in magic tricks. However, think for a few minutes about the “real” purpose for which an egg was designed.

Eggs and Chickens

hen One way in which hens and human females are similar is that both ovulate on a regular basis, even if the eggs which are produced aren’t fertilized. As you hopefully know, human females ovulate about once every 28 to 29 days, and the vast majority of those eggs never get fertilized, but the woman has her period, instead. Similarly, hens ovulate about every 1½ to 2 days. One difference is that after ovulation, a hen’s reproductive system will subsequently add a yolk and albumen to the actual egg, then coat the whole thing with an eggshell, prior to releasing it from her body. Those unfertilized eggs are packaged into cartons and sold in our grocery stores.
(This is Morwen, a little, 3-lb, Cochin Banty fluff-ball.)

rooster In humans, if a couple has intercourse at just the right time so that his sperm can swim up the woman’s reproductive tract and be present when she ovulates, there’s a good chance she’ll become pregnant. Similarly, if there are roosters around, a hen and a rooster may mate, and his sperm must swim up her reproductive tract to fertilize the actual egg cell before the hen’s body adds the yolk, egg white, and shell.
(This guy is out at Dr. Fankhauser’s farm.)

hen on nest One difference between chickens and humans is that, while a human zygote (the cell that results from the union of the egg and sperm) immediately begins to develop, chicken zygotes can wait up to a week or so to begin development and will only begin development if kept at a warm-enough temperature. That way, a hen has time to lay several eggs in her nest, yet all the chicks will hatch at the same time. After laying a number of eggs, a hen may “go broody” and brood her clutch of eggs (incubate them, sit on them to keep them warm).

chick embryo The warmth provided by her body allows the zygotes to develop into chicks. Regardless of the order in which they were laid, three days after she begins to incubate them, the embryos in the eggs will all look like the 72-hr. embryo in this photograph by Dr. Fankhauser. To insure that the embryos are kept warm enough to develop properly, during the time they are developing, the hen sits on her eggs continuously, only leaving her nest once a day for just long enough to defecate and eat a quick meal.

hen and chick Then, 21 days later, her eggs hatch, and she has a family of fuzzy chicks to raise. They still need to be kept warm for a few more weeks, and she has to teach them what’s good to eat and put up with them jumping up on her back to play.
(Morwen went broody and was given some “adopted” eggs from Dr. Fankhauser’s farm. Here she is with two-day-old Nim.)

What’s in an Egg?

An egg has to provide protection, food, and air for the developing embryo for the whole 21 days. Think about how much space would be needed to store all the food you eat in 21 days! All the vitamins, protein, and energy the embryo chick needs to grow must be packaged into the egg — that’s the growing embryo’s only source of food for that whole time. As mentioned above, the hen’s reproductive tract adds three main things to the egg before it is laid.

One note here about “egg safety:” because egg shells are porous, there is a possibility that washing eggs may actually give bacteria a route by which to enter the egg. If eggs are washed just before use, this would not be a problem because the number of bacteria would be negligible. However, if eggs are washed just after the hen lays them (as is routinely done in “egg factories”), then packaged into egg cartons, then sit for a while until shipped to a grocery store, then sit for a while at the grocery store until purchased, then sit for a while in your refrigerator until used, that may give any bacteria that did enter the egg a chance to grow and multiply, so by the time the eggs are used, the bacterial count may be significantly higher, perhaps enough to make someone sick. To prevent bacterial growth in eggs, if washing is even needed (which it usually is not), they should not be washed until just before use.

How Does It All Fit in There?

So how do you cram 21-days’-worth of nutrition into one egg yolk? The amount of vitamins and minerals needed by a small embryo growing into a small chick is small enough to fit without too much of a problem, and the hen’s body manages to cram sufficient protein into the yolk, too. (Note, by the way, that the nutritional value of an egg is dependent on the hen being well-fed. Hens who live in “egg factories” and only get human-made “laying mix” to eat typically lay eggs with very pale yellow yolks, while free-range, farm hens who get to eat dark-green leafy vegetation, food scraps, etc., typically lay eggs with dark orangish yolks due to the presence of a lot more vitamins.) A bigger challenge is to fit 21-days’-worth of energy (Calories) into as small of a space as possible.

The solution to that problem is rather interesting. You may recall hearing that 1 g of protein or 1 g of carbohydrate stores/provides 4 KCal of energy, while 1 g of lipid (fat, oil) stores/provides 9 KCal of energy. That means that by providing the growing chick embryo with energy stored in lipids (fats) rather than carbohydrates (sugar), the same amount of energy will require only 44% as much storage space. For example, an average egg weighs about 50 g and contains about 5 g of lipids, so that’s equivalent to 45 KCal of energy. If that 45 KCal of energy would be stored as carbohydrate, instead, that would weigh a little over 11 g. That means the overall weight of the egg would have to increase by a little over 6 g, or 12.5% of the original weight of the egg.

vinegar & oil However, there is one small detail to be worked out when storing energy as lipids. That 50-g egg contains about 38 g of water. Granted, a lot of that water is out in the albumen (egg white), but there’s a lot in the yolk, too. As you may recall, and as shown in this photo, oil and water do not mix. This little glass contains vinegar (a water-based solution), which is the brownish liquid on the bottom, and salad oil, which is the pale-yellow liquid on the top. Even if we’d shake up this glass, the vinegar and oil would just separate, again. Thus it won’t work to have an egg yolk that contains just water and lipids, because the same separation would occur there. An egg yolk needs to also contain some substance that would enable the oil and water to stay mixed together.

lecithin The solution is to include lecithin, a type of phospholipid. Note that this molecule contains a glycerol backbone that is bonded to two fatty acid chains (from the bottom two carbons) and to a phosphate group (from the top carbon) that is also bonded on to “something else.” The long, fatty acid chains are hydrophobic, and as such are soluble in lipids such as fats, oils, cholesterol, etc. The phosphate group is ionic, and has a lot of polar oxygen atoms in it, so that “end” of the phospholipid molecule is hydrophilic (water-soluble). Because of that, phospholipids, such as lecithin, are emulsifying agents, substances which are soluble in both oil and water, thereby enabling those two substances to mix together. That forms an emulsion in which the fat is divided into tiny droplets and dispersed among the water-based solution.

Soap is another example of an emulsifying agent: it allows oily “dirt” to mix with water so it can be washed out of one’s clothing or off one’s dishes. Milk and blood are other examples of emulsions.


lemon The lecithin in egg yolk can emulsify a lot more than just what s in the yolk, and that’s the basis of the emulsion known as mayonnaise. In mayonnaise, an egg yolk is used to blend together an acidic, watery substance and an oily substance. There are several conjectures as to the origin of mayonnaise, but the most popular story is that it originated in Mahón in Minorca, Spain, and from there was introduced into France, possibly with the original French name of “mahonnaise” (meaning of/from Mahón, in the style of Mahón). From what I’ve read, in the original Spanish and French versions, olive oil is always used, and either lemon juice or vinegar may be used as the acid. Also, it sounds like while the original Spanish version never contains powdered mustard, in the traditional French version, mustard is always added as a seasoning.

Now, the use of mayonnaise has spread worldwide, and there are many national and “gourmet” variations on the type of acid (lemon juice or any of a wide variety of vinegars), type of oil (olive oil, cheap “salad” oil, or a variety of other oils), and types of other spices (rosemary, basil, hot peppers, etc.) which may be added. There is also a wide variety of other additives, from the sugar and starchy fillers used in commercial mayonnaise (especially “light” mayonnaise) to tomato-based products (tomato paste, ketchup) to pickle relish to blue cheese, etc., which may be added. When mayonnaise is mixed by hand with a whisk, typically only the egg yolk is used, but when mixed in a blender, often the whole egg is added. Some kinds of egg-free “mayonnaise” use lecithin from soy beans. While cheap, store-bought mayonnaise may contain things like distilled white “vinegar” (chemically-synthesized acetic acid diluted to 5%), low-grade, generic “salad” oil, starch and other fillers to mimic the consistency of mayonnaise, and sugar, on the other hand, the taste and quality of home-made mayonnaise can be varied greatly through the creative use of lemon juice or different vinegars (balsamic, wine, malt, cider, rice, etc.), different oils (olive, hazlenut, walnut, avocado, corn, etc.), and different herbs and spices (mustard, chili powder, curry, rosemary, garlic, etc.). Many people who take the time to make their own mayonnaise will use high-quality, organic, cold-pressed oils, and if using olive oil, will also choose extra-virgin (the first, highest-quality pressing from the olives). If using lemon juice, they will squeeze their own from fresh, organic lemons, or if using vinegar, will use an organic vinegar, perhaps a balsamic or wine vinegar. They may also seek out a source for fresh-from-the-farm, organic eggs from free-range chickens, or if space allows, raise their own chickens and use their own eggs. Use of a spice grinder to grind whole spices immediately before adding them to the mayonnaise can greatly enhance the flavor as compared to using purchased, pre-ground spices from which the flavor has had time to “evaporate.”

Recipe for “Generic” Mayonnaise

  1. Your cooperation is requested in keeping the oil in the designated space in the lab room and in using only designated glassware to measure it — if spilled on the floor, it is VERY slippery and dangerous. This recipe makes about 1½ C of mayonnaise, and you should bring a clean container in which to take it home.
  2. Watch as your instructor makes his/her demonstration batch of mayonnaise so you can see how it is done. Your instructor will use some of his/her demonstration batch of mayonnaise to make blue cheese and/or garlic dip, and you are encouraged to try some of that dip and/or your own mayonnaise with the veggies that have been provided (apple slices with blue cheese dip are especially good).
  3. equipment
  4. Gather all your supplies and equipment:
  5. Note that some of the blenders here in the lab have much larger, wider bottoms, and thus do not work well for making a single batch of mayonnaise. If you are using one of those blenders, double-up and work in pairs to make a double batch, doubling all the ingredients used.
  6. Note: here in the lab, “generic” oil and/or vinegar, etc., will be provided, but you are encouraged to try this, again, at home using better-quality ingredients of your choice. Gather all your ingredients and begin to add them to the blender as follows:
  7. kinds of acid
  8. Decide whether you wish to use 2 T of lemon juice or vinegar (or a mixture of them).
  9. juicing the lemon
  10. If you are using lemon juice, you will first need to juice a lemon. Since you need 2 T of lemon juice, if your lemons are small, you may need two, but one “big” lemon should provide adequate juice.
  11. juice added to blender
  12. Place the 2 T of lemon juice or vinegar into the blender.

  13. kinds of mustard
  14. Most recipes include 1 tsp powdered dry mustard. (Note: if you make this at home and have a spice grinder or mortar and pestle, you can grind your own spices to add, but remember the flavor will be stronger, so you may wish to use less.) Add the mustard to the blender.
  15. egg ready to add
  16. Obtain 1 egg. It is often recommended to first put the contents of the egg into another dish to make sure they are OK before adding to your recipe.
    (Morwen donated an egg for the mayonaise in these photographs.)

  17. Mix briefly to blend, then TURN OFF THE BLENDER. If necessary, scrape down the sides with the rubber scraper. CAUTION: DO NOT INSERT THE SCRAPER WITH THE BLENDER MOTOR RUNNING!!!

  18. other spices
  19. Optional ingredients such as red or black pepper, salt, or whatever tastes good to you (some cookbooks recommend up to ¼ tsp salt and/or a “dash” of powdered cayenne pepper) may also be added and blended in at this time.

  20. kinds of oil
  21. Decide whether you wish to use 1 C of “salad” oil or olive oil (or some other kind of oil).

  22. oil ready to add
  23. If you have not already done so, measure out 1 C of your oil, now. Then remove just the center of the blender lid.

  24. With the blender motor running on the highest speed, SLOWLY and carefully DRIZZLE in the 1 C of oil through the hole in the lid. DO NOT DUMP IN ALL THE OIL AT ONCE — IT WILL NOT EMULSIFY THAT WAY. You will hear the sound of the blender change as the mayonnaise thickens. As the mayonnaise thickens, you may also hear the whirring of the blender blades spinning in an air pocket, and if that happens, you may need to turn off the blender to “burp” it (pop/release the air bubble by inserting the rubber scraper into it). Make sure to remove the rubber scraper and replace the blender lid before resuming blending!
  25. mayo in storage jar
  26. Use the rubber scraper to transfer your finished mayonnaise to a clean container with a lid. Optionally, at this point, you may stir in crumbled blue cheese, finely chopped veggies, smashed/diced garlic, or other spices. If you are not the last person to use the blender, you can just scrape your mayonnaise out with the rubber scraper (if you were “creative” in your use of spices, be extra careful about cleaning out the blender for the next person). After the last person makes his/her mayonnaise, the blender will need to be cleaned with hot, soapy water.
  27. After everyone is done, all utensils should be thoroughly cleaned with hot soapy water. Oil is difficult to remove, yet it is very important to do so. Be careful around sharp blender blades. All spilled oil on the floor, countertops, etc. should be thoroughly cleaned up — spilled oil on the floor can be very slippery and dangerous. Carefully clean all spills off the countertop.
  28. Take your mayonnaise home and and store it in the refrigerator. Optionally, grated cheese, onion, and/or any suitable spices or herbs may be stirred into your mayonnaise to give it a variety of flavors. Try your mayo on a sandwich or whatever and record in your lab notebook how it tasted or any other observations.

Other Things to Include in Your Notebook

Frodo Make sure you have all of the following in your lab notebook:

Copyright © 2010 by J. Stein Carter. All rights reserved.
Based on printed protocol Copyright © 1978 D. B. Fankhauser
and © 1988 J. L. Stein Carter.
This page has been accessed Counter times since 18 Dec 2010.