The condiment is an emulsion, meaning it combines oil and water (which ordinarily do not mix). To successfully execute an emulsion, the ingredients must be added slowly while quickly mixing nonstop. If that sounds like a lot of work and finicky technique, it's because it is. Texturally, mayo is so persnickety that Costco's creative team actually pulled the plug on developing Kirkland mayo before the product ever hit shelves. Skip the extra steps, advises Garten, and leave laborious mayo-making to the retailers.
Mayonnaise is an emulsion, known for its difficulty to achieve stability. Costco's attempt to launch a Kirkland Signature mayonnaise was halted due to this challenge.