What are the origins of eggnog? Were there other forms of nog that did not involve egg?

Etymonline identifies eggnog as a combination of egg+nog, which they say was first recorded c. 1775. They point that nog is a regional name (apparently originating around Norfolk, Englandh) for a either a "strong ale" or an "old, strong type of beer brewed in Norfolk".

The Oxford English Dictionary similarly identifies "nog" as "a kind of strong beer brewed in East Anglia" (Norfolk is in East Anglia). We'll return to whether this is actually the origin of nog in eggnog later (spoiler: no one is sure).

The first reference to eggnog is a c. 1775 poem by a Maryland pastor:

Fog-drams i' th' morn, or (better still) egg-nogg,

At night hot-suppings, and at mid-day, grogg,

My palate can regale...

More reference to eggnog/egg nog appear in 1788, in both New Jersey and Philadelphia, pointing to perhaps mid-Atlantic origins for the drink, or at least the name. (More early references here, from linguist Ben Zimmer, probably the best know English-language etymologist, if such a title exist.)

The current (or at least alternative) British name for the drink is "egg flip", which I think gives us good clues to its origin. Flips are a genre sweetened alcoholic cocktail, often heated, that generally contain eggs. We get our first reference to a drink called a flip in 1693. Still today, on both sides of the Atlantic, there are still a genre of cocktail called "[flips](https://en.wikipedia.org/wiki/Flip_(cocktail%29)", but not all flips are hot and the drink is not very popular--mixology has gone another direction.

One mid-19th century cocktail guide ([Thomas Jerry](https://en.wikipedia.org/wiki/Jerry_Thomas_(bartender%29)'s How to Mix Drinks, available in full on Google Books in the 1862 edition) has six different recipes for flips, both hot and cold. The later 1887 edition apparently has doubled that number. The author writes, "The essential in 'flips' of all sorts is, to produce the smoothness by repeated pouring back and forward between two vessels, and beating up the eggs well in the first instance; the sweetening and spices according to taste." It also has a recipe for eggnog (or rather, six recipes for eggnog), but in another sections. The eggnog recipes generally include milk (the one exception is "General Harrison's Egg Nog", which seems to be idiosyncratic), while the flip recipes as a rule do not.

Notably, Thomas states that eggnog, as recipe not merely a name, is American in origin. Unfortunately, he does not connect it with the flip cocktails found elsehwee in his book. A well-traveled drinker (he tended bar in at least six states), Thomas notes, "At the South it is almost indispensable at Christmas time, and at the North it is a favorite at all seasons." Though he identifies eggnog as American, he says "it has a popularity that is cosmopolitan", and that in Scotland it is known as "auld man's milk." Interestingly, one of Zimmer's earliest egg nog references also connects it to Christmas (and in the South, no less). The association between the drink and the season is clearly an old one. There was, for instance, an infamous "eggnog riot" at the US Military Academy at West Point around Christmas time 1826. The commanders tried to cut down on cadet drinking, but the cadets proceeded to spike the non-alcoholic punch and become quite unruly.

Zimmer, as a linguist rather than a historian, does not connect egg nogs to flips, nor to other similar milky drinks like milk possests and milk punches. Possets were originally made from milk curdled with some sort of alcohol, typically wine or ale. Shakespeare mentions them several times. From reading that 19th century barman's guide, the milk punches seem to contain no eggs and the flips no milk. The combination of the two in egg nog might be unique, or it might be a development of the earlier flip or indeed the earlier posset (possets date back to the 15th century). Wikipedia claims that some sixteenth century possets that contained both milk and egg, but this is uncited and in a little searching I've been unable to find historical proof of a posset drink with egg. I emphasize drink because possets of the 18th century were being thickened with biscuits and did not even necessarily contain alcohol (blog has the best history of possets I could find), becoming more like a dessert similar to a trifle than a drink similar to eggnog. So while many people connect the idea of posset to eggnog, the two appear to share a morphology rather than a true genealogy. The connection with the flip seems more sound.

As for how the "nog" of Norfolk got to the Mid-Atlantic colonies, there's no clear connection. Going back to Ben Zimmer, he notes:

The egg part of eggnog (or egg nog) is transparent enough, but no one is quite sure how we ended up with nog. Nog shows up in the late seventeenth century as a regional term for strong beer in East Anglia, the easternmost region of England. A fellow named Humphrey Prideaux wrote a letter in 1693 from the county of Norfolk, describing "a bottle of old strong beer, which in this country they call 'nog.'" One theory for the origin of nog links it to noggin — which, before it became slang for "head," could refer to "a small mug" or "a small drink of spirits." Another suggestion is that the word is related to the Scottish term nugg or nugged ale, meaning "ale warmed with a hot poker."

But, in short, there are other kinds of nog or nugged ale without egg. The origins might strong beer or heated beer or a heady drink some kind, but might also possibly indicate a particular type of mug or a small amount of liquor. However, no one calls those nogs generally (none of those nog appear in America, as far as I can tell), and no other American or English mixed drink seems to have adopted the "nog" into their name, making eggnog one of kind. An alternate etymology connects eggnog to "egg-n-grog", but we have no evidence of anyone ever drinking anything called an "egg-n-grog", so it probably is safe to dismiss it.

Though not everyone agrees, I think it's likely that eggnog came out of the "flip". Some argue it inspired by milk punch or possets. There are many kinds of flip drinks; though they all contain egg, they are made with a variety of alcohols. Thomas Jerry's barman's guide mentioned above lists two rum flips, an ale flip, two egg flip (one with ale, one with cognac and rum), and a brandy flip. Though only two are called egg flips, all contain eggs. You could see these as eggnog's cousins. Alternatively, you could see the milk punch tradition (Thomas lists four recipes) as related, but if so, it seems more distantly related as two of the four they rely on the milk curdling, something unmentioned in eggnogs, and in general seem to have a fairly different preparation procedure involving filtering rather than frothing, as with the flip and egg nog.

Here's two flip recipes with different alcohols (be cognizant of the risks of eating raw egg; to avoid all risk, make sure to use pasteurized eggs, or to live in the U.K. where salmonella isn't endemic):

Ale Flip

Put on the fire in a saucepan one quart of ale, and let it boil; have ready the whites of two eggs and the folks of four, well beaten separately; add them by degrees to four table-spoonfuls of moist sugar, and a half a nutmeg grated. When all are well mixed, pour on the boiling ale by degrees, beating up the mixture continually; then pour it rapidly backward and forward from one jug to another, keeping one raised high above the other, till the flip is smooth and finely frothed. This is a good remedy to take at the commencement of a cold.

Egg flip (another method)

Beat up in a jug, four new laid eggs, omitting two of the whites; add half a dozen large lumps of sugar, and rub these well in the eggs, pour in boiling water, about half a pint at a time, and when the jug is nearly full, throw in two tumblers of Cognac brandy, and one of old Jamaica rum.

Keep in mind the book contains several other flip recipes as well as several true eggnog recipes.

Based on the name "nog" possibly begin associated with beer or ale, I half suspect that the ale flip may have been the first version of the drink to bear the name "egg nog". If so, the more familiar hard spirits derived versions must have been innovated shortly after. However, there's really no direct evidence of this, as the earliest reference Zimmer found that actually indicates what's in the stuff calls eggnog "a mixture composed of new milk, eggs, rum, and sugar, beat up together"; that is, spirit-based, rather than ale-based. It's also unclear which is the original, the cold version or the hot. It does seem as though what made egg nog different from the flip, more than anything else, was the addition of milk, and later cream. It's impossible to tell if this is a later classification method or the original innovation--there could well have also been no difference at all between flips and eggnogs originally, with eggnog simply being an alternative name that caught on regionally. I suspect name eggnog might have been coined to parallel egg flip (remember, flips are never actually eggless so it's not necessary to differentiate the egg flip from any other sort of flip), and egg flip was of course named for how you originally mix up the eggs and alcohol.