"Just Mayo" just isn't mayo, according to federal regulators. (Hampton Creek Foods)

When regulators at the Food and Drug Administration this month accused the company behind vegan-friendly "Just Mayo" of mislabeling its product, they relied on a decades-old government description of what actually qualifies as mayonnaise.

“The use of the term ‘mayo’ in the product names and the image of an egg may be misleading to consumers because it may lead them to believe that the products are the standardized food, mayonnaise,” the FDA wrote in a recent warning letter to San Francisco-based Hampton Creek Foods. The agency said the name "Just Mayo" implies the product is real mayonnaise, when in reality it does not "meet the definition of the standard for mayonnaise."

[FDA: 'Just Mayo' isn't mayonnaise because it isn't made with eggs]

For starters, regulators said, it doesn't actually contain eggs. In addition, it has "additional ingredients that are not permitted by the standard of identity for mayonnaise, such as modified food starch.”

So what exactly is Uncle Sam's official standard for mayonnaise?

[Big Food's weird war over the meaning of mayo, America's top condiment]

For that, you have to dig deep into the Code of Federal Regulations, Title 21, Chapter I, Subchapter B, Part 169, Subpart B.  There, you will find the government's 430-word description of what qualifies as real mayo. The full definition is included below for your reading pleasure. But for any aspiring mayo magnates, here are a few general guidelines to follow if you want to stay in the FDA's good graces:

  1. Mayonnaise must contain "not less than 65 percent by weight of vegetable oil."
  2. Acidifying ingredients. That includes "vinegar or any vinegar diluted with water to an acidity ... of not less than 2.5 percent by weight," or a limited amount of "lemon juice and/or lime juice in any appropriate form."
  3. Eggs! For the love of mayo, don't forget the eggs: "Liquid egg yolks, frozen egg yolks, dried egg yolks, liquid whole eggs, frozen whole eggs, dried whole eggs, or any one or more of the foregoing ingredients ... with liquid egg white or frozen egg white."
  4. Other optional ingredients, such as salt or certain spices, "except saffron or turmeric."

There are a handful of other requirements, including the labeling all ingredients. But those are the basics of harmonious mayo production.

Here's the full government definition for mayonnaise, which appears in the regulations just after the rules for French dressing, but just before the rules for salad dressing and vanilla extract:

§169.140 Mayonnaise.

(a) Description. Mayonnaise is the emulsified semisolid food prepared from vegetable oil(s), one or both of the acidifying ingredients specified in paragraph (b) of this section, and one or more of the egg yolk-containing ingredients specified in paragraph (c) of this section. One or more of the ingredients specified in paragraph (d) of this section may also be used. The vegetable oil(s) used may contain an optional crystallization inhibitor as specified in paragraph (d)(7) of this section. All the ingredients from which the food is fabricated shall be safe and suitable. Mayonnaise contains not less than 65 percent by weight of vegetable oil. Mayonnaise may be mixed and packed in an atmosphere in which air is replaced in whole or in part by carbon dioxide or nitrogen.

(b) Acidifying ingredients.

(1) Any vinegar or any vinegar diluted with water to an acidity, calculated as acetic acid, of not less than 21⁄2 percent by weight, or any such vinegar or diluted vinegar mixed with an optional acidifying ingredient as specified in paragraph (d)(6) of this section. For the purpose of this paragraph, any blend of two or more vinegars is considered to be a vinegar.

(2) Lemon juice and/or lime juice in any appropriate form, which may be diluted with water to an acidity, calculated as citric acid, of not less than 21⁄2 percent by weight.

(c) Egg yolk-containing ingredients. Liquid egg yolks, frozen egg yolks, dried egg yolks, liquid whole eggs, frozen whole eggs, dried whole eggs, or any one or more of the foregoing ingredients listed in this paragraph with liquid egg white or frozen egg white.

(d) Other optional ingredients. The following optional ingredients may also be used:

(1) Salt.

(2) Nutritive carbohydrate sweeteners.

(3) Any spice (except saffron or turmeric) or natural flavoring, provided it does not impart to the mayonnaise a color simulating the color imparted by egg yolk.

(4) Monosodium glutamate.

(5) Sequestrant(s), including but not limited to calcium disodium EDTA (calcium disodium ethylenediamine- tetraacetate) and/or disodium EDTA (disodium ethylenediaminetetraacetate), may be used to preserve color and/or flavor.

(6) Citric and/or malic acid in an amount not greater than 25 percent of the weight of the acids of the vinegar or diluted vinegar, calculated as acetic acid.

(7) Crystallization inhibitors, including but not limited to oxystearin, lecithin, or polyglycerol esters of fatty acids.

(e) Nomenclature. The name of the food is “Mayonnaise”.

(f) Label declaration. Each of the ingredients used in the food shall be declared on the label as required by the applicable sections of parts 101 and 130 of this chapter.

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