Currently, two recognized categories exist for the porter style - brown and robust - according to the style guidelines promulgated by the Association of Brewers (Boulder, Colorado). Both brown and robust porters have identical original and terminal gravities (1.045-1.060 and 1.008-1.016, respectively), but they differ in bitterness, flavor, body, and color. The full-bodied, full-flavor robust porters have 25-40 IBUs and are 30+ °SRM; brown porters are lighter in body and mouthfeel, have 20-30 IBUs, and are 20-30 °SRM.
I propose a reclassified system that recognizes the use of lager yeast strains, brown malt, and dry hopping. My unofficial, proposed classification system follows:
Pennsylvania porter: Pennsylvania porter is the classic American porter of the 19th and early 20th centuries. It is a bottom-fermented, ester-free beer with fair-to-medium mouthfeel that will dry toward the end of the taste and may also include slight diacetyl and burnt malt components. Typically, malt and hops are balanced (O.G. 1.049-1.053; IBUs 20-25), and the hops are characteristically American. It is brown/black in color with red tints or a mahogany cast in the glass.
Certain regional homebrew competitions already recognize what is termed "East Coast Porter." Based on the research presented in this article, this variant could be incorporated into the Pennsylvania porter style.
Prosperity porter: Prosperity porter can be bottom or top fermented and has a chewy dextrin mouthfeel that gives way to malt, caramel, biscuit, and some burnt notes. In keeping with its heritage as a keeping beer, prosperity porter's original gravities are in the 1.070-1.080 range - substantially higher than in the current robust porter guidelines. IBUs are 35-50, with dry-hopping acceptable; hops are noticeable in the nose and taste. Esters are not preferred, although this beer will develop sherrylike qualities with aging. It is brownish-black in color with tints of red in the glass.
Micro porter: A tribute to modern craft brewers and their penchant for experimentation, micro porter holds the greatest amount of latitude for gravities (1.048-1.070) and bittering (30-??). The beer is top fermented and highly hopped with maximum alpha-acids, possibly dry-hopped, and may have esters. It has medium mouthfeel and body. Caramel notes together with burnt notes are typical; biscuit or toasty notes are acceptable. It has a deep brown/black color that may be opaque or have reddish highlights.
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