by Julia Thiel
A few, as it turns out—including Michael Ruhlman. Aged eggnog is nothing new (though most people don't wait an entire year to consume it). It's likely that back before modern technology, when hens didn't lay eggs in the winter, eggnog would have been made in the fall and then kept in a cool place until the holidays. George Washington reportedly created his own eggnog recipe involving rye whiskey, rum, and sherry, which he'd let sit for several days in a cool place. According to indepthinfo.com, it was "reputed to be a stiff drink that only the most courageous were willing to try." And many of the recipes for aged eggnog that have surfaced online date back to the late 19th and early 20th century. (Sadly, there were none in the old cookbooks I recently wrote about.)
Whether it's three weeks old or three years old, aged eggnog is actually safer to drink than fresh eggnog made with raw eggs—as long as you put plenty of booze in it. (Not that raw eggs are all that dangerous in the first place. The USDA estimates that one in every 20,000 eggs contains salmonella bacteria, which means that the average consumer would encounter a contaminated egg once every 84 years.)
In 2009 microbiologists at the Rockefeller Institute for Medical Research decided to test their hypothesis that the alcohol would kill any bacteria in the eggnog they made in the lab every holiday season (from the late Dr. Rebecca Lancefield's recipe). They made the eggnog before Thanksgiving as usual, but added enough salmonella to mimic getting between one and ten bad eggs to the recipe and then tested it for bacteria over a three-week period. Adding the alcohol immediately reduced the number of bacteria, but there were still plenty left. After a week there were still quite a few, but after three weeks the eggnog was completely sterile.
The ratio of alcohol to other ingredients matters for sterilization, of course. Science Friday's Flora Lichtman, who's covered the Rockefeller experiments, said that the concentration of alcohol in the finished eggnog is 20 percent. But when Cook's Illustrated tested out the recipe, they found that it was 14 percent alcohol, which matches up pretty well with the 13.5 percent ABV that I calculated (I assumed that they used 80-proof alcohol and large eggs).
When I made eggnog last year (from this Chow recipe, via Michael Ruhlman's blog) I found that aging for a few weeks did indeed tame the alcoholic burn of the eggnog—while it didn't make the nog taste any less boozy, it did seem better balanced. Three weeks ago I made the same recipe and put it in the fridge to age alongside last year's batch, and earlier this week I did a side-by-side tasting. The three-week-old eggnog tasted much like I remembered it from last year's batch: rich, creamy, and sweet, with an alcoholic kick that lingered on the finish.
Pretty much every article I'd read said that aged eggnog will continue to improve the longer you keep it—Ruhlman tried a two-year-old eggnog a few years ago and loved it—but I did find one blog post that disagreed. Last year Booze Nerds tried six different versions of the same eggnog recipe (not the one I used), fresh and aged for up to five weeks, with all the one-week intervals in between. They described the four- and five-week-old versions as having an "eggy, almost metallic flavor" that they didn't like; the three-week-old eggnog was the favorite. I didn't taste any metallic flavor in my eggnog, but I wonder if what they were describing was similar the sharpness I noticed in the year-old eggnog.
I later tried a toned-down version of each version (two parts eggnog to one part milk/cream mixture), which allowed the flavors of the more aged eggnog to come through better. By comparison, the three-week-old eggnog actually seemed a little flat—very creamy, but with less complexity than the more aged version. They're both very good (in small quantities), but I'd probably add a little less milk and cream to the younger one.
If you want to age your favorite eggnog recipe, Cook's Illustrated offers this tip to ensure that you include enough alcohol to sterilize it: use at least 1.5 ounces of 80-proof liquor for every egg, and don't add the dairy until you're ready to serve it. It's getting a little late to age eggnog for Christmas, but if you made it this weekend it would be ready to drink before New Year's. Or you could live on the edge and try it after just two and a half weeks, since the odds that it's infected with salmonella in the first place are very low. If you'd rather not risk it, just use pasteurized eggs.