A brewer's-eye view of beer, in an open fermenter, at high kräusen: that is, yeast in fine fettle!
Top fermentation, generally associated with ales, is a mode of fermentation in which the flocculating yeast rises to the surface of the fermenting wort, rendering it possible to 'skim' the crop of yeast from the top of the vessel, ready for transfer to the next batch of wort. <...> High kräusen is a German term, also widely used in English, which refers to the large, billowing, unkempt head of foam that forms on the surface of beer at the peak of fermentation. <...> In a traditional fermentation cellar, beer ferments in open vessels that allow the brewer to visually control different stages of fermentation.
—The Oxford Companion to Beer
This is a fermentation panorama that most American 'craft' brewers don't often see, because most do not ferment their beers in open fermenters. Nor do they experience the full redolence of yeasty aromas which waft from open fermenters.
But the brewers at Bluejacket —a brewery and restaurant, newly opened in Washington, D.C.— do.
The photo is courtesy of Bobby Bump, lead brewer at Bluejacket, who posted it to Twitter, 23 November 2013. The beer will become a Belgian-style blond ale, yet unnamed.