Bog Nog is one of our most popular winter seasonals. In most of our kettle sours, the sweetness of fruit balances the acidity of the sour base, but cranberries are so tart that this is certainly the most sour beer we regularly make.
For those who may not know what a kettle sour is, I’ll give a quick explanation. Most sour beers these days get their acidity from Lactobacillus, the same kind of bacteria that gives yogurt its tang. This bacteria takes simple sugars and turns them into lactic acid. We can and do use Lactobacillus in our fermenters, in conjunction with yeast, and that’s called mixed fermentation. This method can make some great sours, and in general it’s fair to say they have a complexity that kettle sours lack, but it has some big drawbacks. The biggest is that once Lacto is in your equipment, it’s really hard to get it out. Tanks, hoses, everything that beer touches, has to be basically nuked if we don’t want all of our beers to end up tasting sour.
Kettle souring, on the other hand, doesn’t lead to any concerns about contamination. Basically, we do the entire first half of the brewday, until the kettle is full and about to boil. Then we cool it down to the bathwater temp Lacto thrives in and add a bunch of bacteria, right in the kettle. By the next morning, that kettle is full of sour wort. Then we proceed with the rest of the brewday, starting with boiling the wort in that kettle, which kills all those bacteria, and presto! No contamination! We pitch yeast to finish the fermentation, and add the fruit toward the end of fermentation. Kettle sours lack a bit of the complexity one can get from a mixed-fermentation. But in a beer that fruit will dominate anyway, this isn’t really a big deal, and a totally reasonable tradeoff.
The base of most of our kettle sours is about half and half pilsner malt and malted wheat, with very light hopping. The fruit amounts vary, but in the case of Bog Nog it’s about 130 pounds of cranberries for a full batch.
Bog Nog pairs well with a flourless chocolate cake or torte, and with turkey sandwiches.
ABV: 5.9%, Bitterness in IBU: 8, Color SRM: 3, Fermentation Temp: 40C/22C, Grain to Glass: 18 days