This flavor is less offensive to me compared to other off-flavors on this list. If you didn’t add vegetables during the brewing or fermentation process, but your beer tastes like veggies, there could be several reasons for this. If you used a lot of Pilsner malts in your beer, it might be susceptible to Dimethyl sulfide (DMS), which some describe as a canned corn, cabbage, celery, or onion-like flavor. DMS is produced during the malting process, so if your recipe has a high proportion of Pilsner malt, extend the boiling time to 90 minutes instead of the usual 60.
If Pilsner malts are not the cause of the vegetal off-flavor, it’s possible that certain hop varieties are responsible. Some types of hops can give off flavors reminiscent of garlic, green onions, grass, or hay. If you don’t enjoy these flavors, try using different hop varieties next time.
If you dry-hopped your beer, this could also contribute to the off-flavor. Most professionals recommend dry-hopping for no more than one week. As with other flavors on this list, too much dry hopping can result in a negative impact on the beer’s taste. Avoid dry-hopping your beer for four weeks, or you may regret it.
If your beer tastes like freshly-cut grass, you may have a grassy off-flavor. Again, similar to other off-flavors on this list, this may not necessarily be a bad thing. Certain hop varieties naturally have a grassy flavor, especially when added late in the boiling process or during dry hopping. If you didn’t use these hop varieties, it’s possible that too many hop particles made their way into your beer. Normally, most of the hop particles are filtered out when transferring the wort from the kettle to the fermenter. If your strainer is not effective enough, consider racking your beer from the kettle to the carboy next time. If that seems like too much work, try using a different hop variety with a higher alpha acid content. This will allow you to use a smaller quantity of hops while still achieving the desired bitterness.
Similar to the vegetal off-flavor, if you dry-hopped your beer, this could also contribute to the grassy flavor. Most professionals recommend dry-hopping for no more than one week.
This off-flavor is a variation of the first one on the list (alcoholic) and the fourth (estery) and can be caused by the same problem: high fermentation temperatures. When fermentation temperature is too high, yeast produces more esters. Unfortunately, some esters can remind us of the smell of nail polish remover, paint thinner, or super glue. In the past, I used to pitch my yeast as soon as the temperature reached the upper limit of the yeast’s ideal range. As I eventually learned, this created a problem. The wort continues to warm up during fermentation, especially in the first few days. This often leads to off-flavors. It’s better to pitch the yeast at the lower end of the temperature range, allowing the wort to warm up within the ideal temperature range. If temperature control was not the issue, it’s possible that your beer was oxidized.
Technically, the term for this off-flavor is “astringency,” but most of us who have tasted young red wine would recognize it as a tannic flavor—the sensation that makes your mouth feel dry and makes you want to pucker up. I experienced this flavor once when I misread the temperature during the mashing process. I had the temperature too high, which extracted tannins from the grains. The temperature during the mash should not exceed 168-170°F (76°C).
If you enjoy the taste of a musty library, you might prefer a peaty scotch instead. In beer, musty flavors can resemble the smell of decomposing yard waste, rotten wood, old books from your grandfather’s collection, or even your attic. Or worse, it can be similar to the smell of a wet towel left in your hockey or gym bag. The best defense against this moldy off-flavor is thorough sanitization. If you are absolutely certain that you followed proper sanitization steps, you may be dealing with moldy grains. Alternatively, if you are confident that you used fresh ingredients, your beer may have been oxidized.
Acetaldehyde can be found in various foods we are all familiar with, such as coffee and ripe fruit. Think of tart green apples or dry cider. Yeast produces acetaldehyde during primary fermentation in almost every beer. Normally, yeast consumes acetaldehyde later in the fermentation process, preventing this off-flavor. However, if your fermentation was not healthy, enough acetaldehyde will remain. Like most of the off-flavors on this list, you can avoid it by ensuring proper sanitization of all equipment and anything that comes into contact with your wort, especially after the boiling process. Make sure to aerate your beer well before adding the yeast and avoid introducing oxygen into the beer once fermentation is complete. Also, don’t bottle your beer too soon.
Sulfur is the technical term for this off-flavor. Apparently, it is a common smell when fermenting lagers. In this case, it is completely normal. All yeast strains produce a by-product called hydrogen sulfide. Fortunately, for ale brewers, the vigorous fermentation process usually eliminates this flavor. But if you brewed an ale and noticed that unpleasant smell, you might want to consider using yeast nutrient next time to ensure a vigorous fermentation.
Phenolic compounds contain hydroxyl and carbon molecules, which are responsible for many of the flavors we enjoy in food, such as the spiciness in chili peppers, the distinct flavors of cloves, cinnamon, and nutmeg, and the smoky aroma found in many Scotch whiskies. Like many other off-flavors on our list, these compounds can be desirable in beer. However, if it was not your intended taste profile or if your beer has a chemical or plastic-like flavor, you may have encountered one of the following problems:
You may have too much chlorine in your water. Try using bottled water to see if it improves the taste next time.
Your choice of yeast strain may be the cause. If you don’t appreciate this flavor, opt for American or British yeasts instead.
Sanitization is also a possible issue. Despite what I mentioned earlier, wild yeast could be the culprit. Pay close attention to sanitization during your next brew, and consider replacing your hoses if you have been using them for a while. I personally prefer to buy new hoses after 10 brews, just to be safe.