Sure, a few innovative brewers have managed to successfully pull off the odd cucumber Pils or sweet potato porter, but such examples are rare, and even well-done veggie beer typically features the produce aisle in only a supporting role.
Occasionally, though, you may find that a beer tastes plant-like even when you’ve stuck to only Reinheitsgebot-approved ingredients. In these cases, the issue is likely more one of process than it is of produce. Here, then, are a few common culprits and some suggestions to solve them.
Dimethyl sulfide (DMS) is usually described as having an aroma and flavor reminiscent of canned corn, but some individuals perceive it as cooked vegetables, especially cabbage, onions, or celery. DMS arises naturally as part of the malting process, but the heat of kilning usually eliminates this volatile compound. However, in very light malts, especially Pilsner varieties, the duration or intensity of kilning can be insufficient to fully drive DMS away. In wort prepared with a large proportion of Pilsner malt, an extended boil of 90 minutes or more is recommended.
Certain hops varieties, such as Summit, remind some tasters of garlic or scallions. Hallertauer Hersbrucker can occasionally come across as grass or hay. These qualities are as intrinsic to these hops as the pine and grapefruit that typify other varieties. If your latest pale ale reminds you of onion dip or a hay bale, then try using different flavor and aroma hops next time. (Note that hay-like qualities may indicate hops that were harvested prematurely. You’re unlikely to run across this in commercial hops, but keep it in mind if you grow your own.)
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Kettle hops material can be significant, especially in IPAs and other hops-forward styles. While little can be done about late additions, hops matter can be reduced by using high alpha acid varieties for bittering. Look to such cultivars as Chinook, Warrior, Magnum, and Apollo for appreciable bittering potential. In extreme cases, consider using an extract of hops oil, available commercially as HopShot syringes.
Dry hops deliver incredible hops aroma, but brewers need to take care not to leave dry hops in contact with beer for too long. Alcohol acts as a solvent to efficiently extract hops aroma compounds, but extended contact can also dissolve unpleasant vegetal aspects. Most professional brewers with whom we’ve spoken recommend a dry hopping period of about a week.
While subtle grassy notes can be appropriate in small amounts for farmhouse styles, vegetal characteristics are almost always considered flaws. Carefully considering your ingredients and process can effectively reduce or eliminate your vegetation frustration.