After pulling out the oil for last post’s vinaigrette, I had a hankering for another oil based dressing – mayo. I rarely bother with homemade mayo, because I always have a jar of Hellmann’s handy…but I was out. So, I yanked my vegetable oil from the shelf, rolled up my sleeves, and started whisking.
Mayo is an extraordinary example of a stable emulsion. Under usual circumstances we all know that water and oil don’t mix. But, in a stable emulsion, water and oil have been combined under constant agitation to form a di-phase system. Tiny droplets of the discontinuous phase have dispersed and suspended into the continuous phase. (The most stable commercial emulsions are created with high-shear processing equipment to form these tiny droplets. However, producers carefully watch their flow/pressure parameters on this equipment, as too much shear will cause stable emulsions to break.) 
Many food formulas exist where temporary emulsions destabilize into separate water and oil phases. (You’ve seen this occur in two-part vinaigrettes – even after shaking, the oil and water are attracted back to themselves.) In cases where a stable emulsion is required, we turn to emulsifiers. Emulsifiers are molecules with a hydrophilic (water-loving) end, and a hydrophobic (water repelling) end. Thus, the emulsifier acts as link between oil and water components in a formula. With mayo, the egg yolk (specifically the lecithin in egg yolk) acts as an effective emulsifier. Other examples of emulsifiers you may find on the labels of foods you love: polysorbate 60, polysorbate 80, lecithin, mono and diglycerides, and more.
Mayo provides reasonable functionality in an array of recipes. A really good mayo prevents water from weeping out in cold potato/pasta/tuna salads, reduces oil pooling in hot dips, and binds yummy ingredients in a crab cake.
Homemade mayo is a quick recipe to make in your own kitchen, and it can give you a decent arm workout…but if you ask me, when you bring out the Hellmann’s…you bring out the best. (wink! wink!)
A Food Science tid-bite: Margarines, ice cream, creamy dressings, several sauces, some meats, and some chocolates utilize emulsion technologies in their formulas. Check out the labels on these products, and let me know what you find. Want a quick emulsifier for homemade sauces and dressings? Prepared mustard can work wonders.
Source: Genevieve L. Christen, ed and J. Scott Smith, ed. Food Chemistry: Principles and Applications. Science Technology System, 2000
I love your blog!I came across your site from the foodieblogroll and I’d love to guide Foodista readers to your site. I hope you could add this homemade mayonnaise widget at the end of this post so we could add you in our list of food bloggers who blogged about mayonnaise,Thanks!
Hi Alisa. Thanks for your interest! I’ve added the Foodista link to the post.
Food Science Secrets readers: If you haven’t done so already, check out Foodista.com – you’ll find a tempting stash of recipes and cooking techniques.