IPAs fail in three areas: wort production, fermentation, and distribution/retail.
Many brewers often overlook the importance of water chemistry when making hoppy beers. Higher than desired mash pH can darken wort (not yet fermented beer) and muddle the crisp flavors of hops. This is the same reason baking soda is used in pretzels. The high pH encourages a mallard reaction (caramelization) to give the pretzel it’s nice brown appearance, but we don’t want too many of these types of reactions in our session IPA. Poorly filtered or non-filtered water can also contribute unwanted chlorine which, again, may lead to a malty flavor and inhibit yeast activity. In addition, if the brewer fails to bypass a water softener, they can end up brewing with water high in sodium, which can add a fullness and sweetness at low concentrations, and contribute a salty flavor at higher concentrations. Two popular brewing salts are calcium sulfate (gypsum) and calcium carbonate (limestone). The ratio of these two salts contributes to the perception of malt and hop flavors. Brewing water with more gypsum than limestone will accentuate crisp, hop bitterness, while brewing water with more limestone will accentuate full mouthfeel and malty characteristics. Obviously, full-mouthed, sweet, salty, dark malt flavors aren’t what we are going for wit these hoppy styles, so the importance of brewers understanding their water chemistry cannot be overstated.
Once the wort reaches the cellar, the yeasts begin to ferment the beer in two stages aerobic and anaerobic (with and without oxygen). If the yeasts are not healthy or there are not enough of them, the oxygen may not be completely consumed and may darken the beer. A cooked vegetal flavor indicates an off flavor compound called DMS and can be caused by not chilling the wort quickly enough after boiling. Diacetyl is a compound most popular as microwave popcorn butter flavor, but it is commonly produced during fermentation by brewer’s yeast. The thing is, the yeast will also metabolize this compound and render it tasteless if given enough time with a warm enough temperature. This flavor can indicate the process may have been rushed out of the brewery before the yeast could clean up the beer. DMS and Diacetyl are also common flavors that indicate infection, so only the brewer knows for sure. The consumer will know they hate the beer, but will they know who to blame? The brewer? The cellarman? The infected lines at the bar? The answer may be all three or something unknown along the way. The most common causes of IPA fails in the cellar include inappropriate yeast pitching rates, over filtering, poor sanitation, oxygen exposure, the physical action of pumps beating up hop oils, and improper storage temperature.
Sherry and cardboard flavors are a symptom of distribution and retail problems, mainly the degradation of hop oils and alpha acids due to oxidation, age, high temps, or a combination of the three. This oxidation also affects the malts by making the beer darker and maltier. When an abused or neglected beer is poured, the color will appear darker than expected. The lack of head retention will also be noticeable by observing the size of the bubbles. Hop oils play an important role in the structural support of the tiny bubbles that create a nice, pillowy head. When these oils are degraded, the pressure of the escaping CO2 becomes greater than the strength of the bubble wall. This leads to a premature collapse of the head. A quality hoppy beer should have a nice layer of bubbles to the last sip, even without agitating the glass. An abused hoppy beer will have its head collapse almost instantly. Common causes for these types of flaws include oxygen ingress at packaging, lack of cold storage at any stage of distribution, poor rotation of inventory, and over-purchasing by retail accounts.
Brendan Megowan, “Common IPA Fails”, Beer Paper LA (February 2016), 21.