This FAQ guide to debugging a problem rather than as an easy to read novel. Its main intention is to help the fermentation specialist isolate the problem and fix the process issues immediately.

Different unique flavors and aromas
Flight of craft beer for tasting and sensory notes

It is perceived as artificial butter, butterscotch, caramel or toffee aroma and flavors. Sometimes it expresses as a milky slickness on the tongue. It is caused by inadequate boiling or oxygenation of the wort. 3-7 days of Diacetyl rest (slightly raising the wort temperature ~20-25OC towards to end of fermentation) helps in controlling it, as the yeast will naturally metabolize these away. Diacetyl is often confused with kettle caramelized malty notes. A bit of training can help isolate the two very different faults.

If not taken care of, this can cause serious hangover or headache in beers.

Green apple-like aroma and flavor. Although Acetaldehyde is a natural precursor to ethanol formation, its residual levels in the finished brew is not desirable. At excessive levels, it might even give a paint solvent/ nail polish smell. One of the primary causes of this sensory note is insufficient healthy yeast count. Making a vigorous starter batch and ensuring adequate oxygen and nutrients could help. Most home brewers give a Diacetyl rest for 3-7 days to help minimize the problem. A slightly warm conditioning and patience is all it takes for the yeast to metabolize some of the unwanted Acetaldehydes and Diacetyls naturally.

Another reason for acetaldehyde is fermenting inverted sugar instead of natural unpasturized honey during mead making. Adulterated packaged honey is therefore avoided by mead makers.

Sulfur (H2S) – The aroma of rotten eggs or burning matches from the beverage is a result of H2S residue. It gives the beer a smell of the LPG gas or decomposing organic waste. It is a sign of stressed yeast. The easiest way to replicate (in your experiments) is by using bread yeast to produce ethanol (stressed yeast= high sugar, high alcohol and no oxygen). Amateurish quest to produce the highest ABV possible of adding too much sugar in wine and malt in beers will also yield these Sulfur aromas. Using the right strain of yeast, adequate oxygenation and nutrients help in keeping the problem at bay. Winemakers and brewers use a few drops of copper sulfate to remove these unpleasant flavors. However, use it sparingly because of copper toxicity regulations in food.

One of the easiest way to get rid of this smell is:

  1. Use proper brewer’s yeast instead of baking yeast for fermentation
  2. Fine with a few drops of copper sulfate solution.

Your home brew has the stench/ smell of a skunk? It is a result of improper handling and storage of beverages (especially imported bottles). Hops react to riboflavin (from grain) under UV light to produce this skunk flavors. This is the reason why we keep the beers in dark bottles away from sunlight.

That being said, white wine is also very susceptible to UV light. In wine, it is called ‘goût de lumière’, which means the taste of light especially in sparkling wine. In some light beers, patrons add a slice of lime before serving. This is to mask these skunk notes.

Ever wondered why Corona beer is served with lime? Imported beer in clear glass gets skunk and citrus notes help mask the off flavors.

Rotten Vegetal – Similar to cooked, canned, or rotten vegetable aroma and flavor (cabbage, onion, celery, asparagus, etc.) One whiff of the brew is all it needs to detect it. If it smells like the LPG or propane gas, then probably they have contamination issues. In wine, it is often a result of excessive contact with dead yeast post-fermentation. Breakdown or autolysis of yeast cake at the bottom is the culprit.

The industry is moving to conical fermentation, which allows aging and storage in the same vessel without raking. Home-brewers, unfortunately, have to rake their wine every couple of weeks to remove the dead yeast (aka lees or yeast cake) sediments. If you are too worried about oxidation, pumping some CO2 in the new container before raking would help. CO2 being heavier than air provides a shield against oxidation.

Buttery, Waxy Goat Cheese: These are the buttery flavors often characteristic of wild fermentation. The yeast produces fatty acids (especially caprylic acid) to impart these notes in the brew. It is desirable in Lambic beers and prolong cask-aged wine. Some winemakers introduce Lacto-malic culture to induce these notes. However, using improperly stored or oxidized hops can also introduce these cheesy notes.

Rancidity: smells like baby vomit or putrid smell of spoilt dairy. This is caused by butyric acid because of the breakdown of fats. It is usually caused because of contamination. Another reason is the use of oily ingredients (nuts, Choco butter etc.) whose fat breaks down during fermentation. An untrained taster often confuses it with DMS

At low levels a sweet, cooked or canned corn-like aroma and flavor. These Sulphur based compounds are produced during germination. The precursor is SMM (S-methyl methionine) that is converted into DMS. Stale and improper malting is the primary reason for this fault. Other reasons could be improper mashing, cooling the wort slowly and wild yeast infection. It is often confused with Rancidity.

This is one of the most common faults in amateur home brew. It could be because of process issues or improper bottling and storage. It is discussed in detail in the links.

Grainy, husky beers: Similar to nutty, harsh flavors of fresh green wheat. It is often prominent in home brewers using self-malted grains. Giving the malt a 2-4 weeks rest (in paper bags) helps get rid of it. In addition, improper mashing can cause it. Avoid mashing for more than 2 hours or over-sparging with boiling water.

Estery: Aroma and/or flavor of any ester (fruits, fruit flavorings, or roses). Personally, I like a bit of banana notes with my wheat beers but too much of anything is undesirable. The usual culprit is poor temperature control. Each yeast has different thermal sensitivity. The same yeast can give clove flavors at low temperatures but banana/ fruity notes at high temperatures. Maintaining lower and constant temperatures is the key to keep them manageable.

However, isolating the contribution of the fruity notes from the fruits/ flowers/ hops and that from the yeast cannot be done without access to the recipe. Making a tea from the ingredients is the first step towards understanding these notes before altering the fermentation temperature conditioning.

Metallic: Tinny, coiny, copper, iron, or blood-like flavor. It could be an equipment, ingredient or a process issue. Fermenting in aluminum or non-food grade fermenters is the usual culprit. Commercial breweries install a powerful magnet at the end of their grain mill to pull out any metallic shavings from the grain and keep these flavors at bay. Some fruits, especially the beetroot has a prominent metallic flavor and should be avoided. In Eastern India (especially near mines), this could be an indication of groundwater contamination.

Using RO water and monitoring the wort chemistry would help. New stainless steel equipment also gives these flavors, probably because of micro-scratches and free ions on the metallic body. A strong acid wash, followed by alkaline neutralization helps to remove it from the brand new equipment.

Sour/ Acidic: Excessive tartness in aroma and flavor. It can be clean (lactic acid) or sharp vinegar-like (acetic acid). PH below 3.0 is a sign that ethanol was oxidized to acetic acid and there is probably no recourse. At mild levels, pH (especially in wine) can be altered by the addition of some Calcium Carbonate (food grade chalk powder CaCO3). Vinegar CH3COOH in Latin means sour wine, which can be a reflection of how common this problem is.

If too much acetic acid is there, we will get a burning sensation in the nose, which is not desirable. In some beers like Gose, Wild Ales, Weise and Sour Beers, a slight amount of tartness is desirable. However, do check the mashing process if the wort is getting sour. At low levels, it is often hard to distinguish between acetic acid and lactic acid sourness. Here, the smell comes handy. Lactic acid has no smell but vinegar has a distinct smell of nostrils burning.

This is usually caused by using old expired hops. At low levels of oxidation, one gets the catty notes (cat urine, tomato or grape leaves). However, at a higher level of degradation, one gets the cheesy notes. Making hop tea from the ingredients helps to identify them early. Storing hops in oxygen-free and inside a refrigerator helps counter this issue. In wine, larvae of some insects when crushed also yield similar urine like rancid bitter notes.

This could be due to a variety of reasons.

  • Firstly improper mashing which leads to many unfermentable sugars.
  • Secondly incomplete fermentation due to poor yeast health. One of the easiest way to replicate this is by using baker’s yeast for making beers from the same wort.
  • Stuck Fermentation.

Although Indians have a slightly sweet palate, but excessive sweetness in beer is a flaw. To deliberately introduce residual sweetness, one could use crystal/ caramel/ carapills malts. Milkshake IPA and milk stouts have added lactose (an un-fermentable sugar) to get a balanced sweet palate.

Phenolic: Spicy (clove, pepper), smoky, plastic, plastic adhesive strip, and/or medicinal (chlorophenolic) like smells and flavors. German wheat beers and some English styles need these notes but often too much of a good thing is also bad. Another problem is that it can come from a variety of reasons, so debugging takes longer.

  • Culprit to be root caused is the chlorinated water, which gives medical and bleach-like aromas.
  • Second could be the yeast strains, try switching to a strain with a crispier finish. English stout yeasts are often attributed to clove flavors.
  • Third is the sanitizer residue especially iodine and chlorine. Try switching to a rinse-free sanitizer.
  • Fourth, mashing technique: Over sparging, using too hot water or even crushing the grain too much can introduce these notes.
  • Fifth and the most obvious reason could be adding excessive spices. Spices lead to an increased warmth perception (higher perceived ABV) which is why some winemakers deliberately add excessive cloves and whole spices (garam masala) in their wine.
  • Lastly, in wine, this is called ‘Brett’ wine because of the yeast Brettanomyces strains (contamination) that were introduced in the vat.

Campden powder can be used to remove chlorine from your brewing water.

Musty/ Earthly: Stale, musty, or moldy aromas/ flavors. Sometimes earthy notes like mushroom and beet are perceived. It is usually a sign of fungal contamination and should be taken seriously. If there are any wall seepage and waterlogging issues, they should be fixed immediately. Using a humidity controller and proper sanitization also is also recommended.

In wine, it is called cork taint, because the cork was not kept soaked in wine during aging (bottles were kept upright instead of at a slant in the cellar). It is often caused by the compounds called  2,4,6-trichloroanisole (TCA) or 2,4,6-tribromoanisole (TBA).

Cork taint: wine faults

If there are signs of malo-lactic fermentation (small microbubbles in wine during secondary that does not disappear), then adding Potassium Sorbate (wine stabilizer) before back-sweeten can also introduce these earthly notes.

The addition of some herbs, mushroom, cannabis/weed/hemp, etc. can also introduce these Earthly flavors. A bench test of these additives can root cause the culprit.

Yeasty: A bready, sulfuric or yeast-like aromas or flavors. It is most often because the beverage is not aged properly and has too much yeast floating around. The quickest way to get rid of them is to wait for a couple of weeks under an airlock.

Some gelatin beer fining agent and 24 hours of cold crash (keeping finished fresh ferment in a refrigerator) often does the trick to remove these off-flavors.

Diamond: Chemically these are Potassium Tartrate crystals, at the bottom of the wine bottles. Wine with excessive levels of tartaric acids tend to exhibit these diamond/ sugar like structures during aging. The best way to get rid of them is to cold crash (24 hours at 4o C) and then bottle. It is a sediment in the bottle and does not affect the sensory perception in any other adverse way. One of the reasons expensive wine bottles have a dimpled base is that these crystals are stuck to the dimple structure at the bottom and are not poured out in the wine glass.

Heat Damage: It is a common term used by experts to describe anything that they suspect was improperly stored and handled. The notes from heat damaged IPA (hoppy beers) and wine are similar to over-aged and oxidized beverage. Hence, heat damage gets more blame than it should deserve. The best way to prevent heat damage is by storing your hoppy beers and wine at less than 13 degrees Celcius.

It is an unusual name for viscous, slimy and fatty mouth-feel in wine. It is often a result of mallo-lactic fermentation. Wine styles with excessive dextrins and polysaccharides are known to exhibit a fatty feeling on the tongue.

Ever felt a whiskey/brandy like feeling when drinking home made wine?

The aroma, flavor and warming effect of ethanol and higher alcohols. Sometimes described as hot. It can also be a result of adding too many spices like cloves & cinnamon in the brew. It is desirable in spicy Christmas beer and heated winter wine. It is a result of high temperature fermentation or stressed yeasts. The biggest problem is that this reduces the amount of beverage that can be gulped in one sitting. Hence, most winemakers and brewers like to keep higher alcohols to the minimum.

Astringent: Puckering, lingering harshness and/ or dryness. When in excess, it impacts the finish or aftertaste by introducing harsh graininess and huskiness. In wine, it is often a result of excessive contact with grape skins. Reducing the contact with the skins and tannins used rectifies it. In beers, it could be because of too much of peated malts, smoked or biscuit malts. Another reason could be over mash or over sparge (which releases the grain astringency). Altering the pH and a few trial batches is needed to isolate the source of this astringency (grain, hop or water). The reason for aging wine and certain styles of beers is to mellow down this astringency through certain natural biochemical reactions. Aged bottles are more valuable because of this unique flavor profile. Saving the astringent bottles for next quarter or year is always a good idea.

This is probably due to Refermentation. Common problem in inadequately pasteurized or preserved sweet wine. This is discussed in the post on Haze and can be cured by adding potassium sorbate or stabilizer in sweet wine.

For champagne they keep it in a rotating neck freezer so that all yeast crystallizes on the cork and when opened gets expelled.

Grassy: Aroma/ flavor of fresh-cut grass or green leaves. Some hops and herbs especially Saaz hops have such a feeling. Fresh hops that are not dried properly also give these grassy notes. Many Indians who grew up drinking jaljeera and herbal teas actually like these notes in their beers. Some home maltsters who use fresh inadequately dried malts also report this problem.

Watery/ Thin: It lacks the body and mouth feel. In wine, it is a result of not using enough fruits. In beers, it is a result of using too little malt or too much enzymes. Adding a bit of specialty malt like caramel/ crystal malts will rectify it. The mashing temperatures can also be altered to produce more sugars that are unfermentable.

Manure: Also called Farmyard smell. It is a sign of improper cleaning of fruits and grapes before pulping. Sometimes in fruit beers, it is a sign of improper puree making techniques. Essentially, there is a degree of composting or undesirable microbial activity. Proper sorting of fruit is recommended to isolate the composted fruits. Most farmyard wine also have other defects associated with wild fermentation.

Solvent: Aromas and flavors of higher alcohols (fusel alcohols). Similar to acetone, lacquer varnish and paint thinner aromas. It is an indication of stressed yeast and is undesirable. Cheap distilled liquor (where the last portion of the distillate is not discarded) often gives these notes. Reasons of the stress could be inadequate healthy yeast count, high gravity (too much sugar), high temperature accelerated fermentation etc.

In mead the common reason is use of inverted sugars or adulterated packaged honey.

Umami: Soy sauce or Thai fish curry aromas and flavors. It primarily comes from amino acids released from the autolysis of yeast. Slight umami flavor is desirable in Sake and some aged beers but it is a difficult flavor to balance. The usual culprit is the beverage was sitting over dead yeast (cake/ lees) for a few weeks. Some brewers have switched to lower protein malts & changes in mashing to reduce Umami. Conical fermenters where the yeast cake can be drained out is recommended to combat these notes.

Floating Film: It is a transparent or sometimes white/ greenish layer on top of the wine (seldom/ rare beers). These films stick to the needles or toothpicks, due to their oily nature. The most common reason is the use of oily ingredients (certain fruits, chocolate butter and nuts) and resinous hops. These can be remedied by tweaking the recipe.

However, wild yeast or mold infection could also result in these flecks on the surface and should not be ignored. Proper sanitation and daily ritual of stirring the wine are known to help.

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कोस पर बदले पानी और चार कोस पर वाणी |
(The taste of water changes every mile and the dialect changes every 4 miles or every village you cross)

Growing up, I thought these words were an acknowledgment of the diversity in India. However, as, I went deeper into food-craft, I realize that this line is a tribute to our senses. Each water body, each village is different and unique, we humans are sharp enough to recognize that.
Multimillion-dollar AI, spectroscopy and scores of lab equipment can at best mimic what our nose, tongue and senses can definitely detect and conclude in an instant. Human senses are tuned to detect some chemicals even in ppb (parts per billion) concentration. This page is a collection of notes on how one can hone their senses and use it for the betterment of food-craft.
Until now, we focused on the basic recipe and flavors. We shared many options of how we could innovate but how those ingredients expressed themselves in the final product was not explore. For food to be called a craft, we need an ability to understand and tweak the more subtle flavors and sensory notes as well.

understand the various flavors and aromas of beer
Craft Beer Flavors Chart

The best way to fix any problem is to isolate it. The above list would help Brewers to critically analyze their homemade wines and home brew beers. Observe the batch to batch variance of your finished product and tweak the processes to rectify the defects. This can also be used to understand the feedback given by judges on your craft brews entry submitted to the competition.

Most professionals use the aroma wheel (for beer, wines or cider) to help explain their sensory notes. I have published a sample wheel for your reference. Amateurs usually perceive the inner circle only, advanced home brewers perceive the middle circle and professional (who constantly train their senses) perceive the outer circle. These aroma wheel are used as a reference guide for those who might end up using similar terms to describe the same sensory notes.

Wine Flavors chart

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Ankur

21 years of experience in Home Brewing and author of Arishtam (India's first homebrew Guide Book).

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