Beer Brewing: Aromas, Health, And You

The aroma of beer is a complex interplay of volatile chemicals that engage our olfactory senses. The process of brewing, including the choice of grains, herbs, yeast, and hops, as well as the fermentation and ageing, all contribute to the unique aroma profile of each beer. While some aromas are desirable, others may indicate spoilage or contamination.

The base grains used in brewing, such as barley or wheat, impart distinct scents. Barley-based beers tend to have maltier, caramelized, and roasted aromas due to the kilning process. Wheat-based beers, on the other hand, lean towards bready, citrusy, and lighter fruity notes.

Yeast is another crucial contributor to the aroma profile, with ale yeast favouring warmer temperatures and imparting stronger scents than lager yeast. The type of yeast used can result in aromas ranging from citrus and banana to sulphur or even baby vomit if wild yeast is involved.

Hops, added during the boiling process, provide bitterness and essential oils that contribute to the bulk of the beer's aroma and flavour. The classic hoppy aroma is characterised by pine, citrus, tobacco, and sage notes, with American hops tending to have higher levels of myrcene, adding a citrus or piney twist.

Other factors, such as temperature, ageing, and exposure to light, can also influence the aroma profile of beer. For instance, beer exposed to sunlight or fluorescent lamps can develop a skunky or sunstruck aroma due to a chemical reaction between light, riboflavin, and hop alpha acids.

While most people enjoy the aroma of a freshly poured beer, it is important to remember that aromas can indicate potential issues. Off-flavours and unpleasant scents may be the result of poor brewing practices, contamination, or spoilage, making it crucial for brewers to understand and control the factors that shape the aroma of their beers.

The effects of aroma on the brain

The human sense of smell is a powerful thing. It can evoke pleasure, disgust, recognition, and memory. Aroma is a major sense that we are not always conscious of, but its effects are often subtle and subliminal.

Aroma detection involves specific sensory receptors in the nose being stimulated by volatile chemicals in the air we breathe. The nose can perceive thousands of different scents, and the brain keeps a record of them, allowing us to recognise and remember them.

A strong aroma can transport the human mind directly into the past, over years or even decades, to a particular place or moment. Aroma has a direct link to the most primitive parts of the brain, and it can affect our emotions and hormones.

Aroma can influence our behaviour in many ways. For example, we eat food faster in brightly lit conditions, and certain aromas are now recognised as enhancing the sales potential of shops. Studies have shown that most people consider a fresh hop aroma to be desirable in a beer, even if they cannot identify the aroma itself.

To detect the aroma in beer, it is important to coat the surface of the glass by swirling the beer before smelling it. This allows a thin film of beer to evaporate into the air, making the aromatic molecules available to the olfactory receptors.

There are many ways to describe beer aroma, and it often depends on the ingredients used in the brewing process. For example, beer made with barley will tend to smell malty, caramelised, and roasted, whereas beer with a stronger wheat base will be more bready and citrusy with lighter fruity notes.

Off-aromas in beer, or "off-flavours", are usually caused by issues during the brewing process or during packaging and handling. Some common off-aromas include:

• Diacetyl: buttery or butterscotch aroma, often caused by yeast issues or contamination
• DMS: creamed corn or vegetal aroma, caused by high temperatures during the boil
• Acetaldehyde: green apple or raw pumpkin aroma, caused by young beer or oxygen exposure
• Esters/Solvent: fruity or perfumey aroma at low levels, but can become nail polish remover-like at higher levels
• Oxidation: cardboard or wet paper aroma, caused by exposure to oxygen during packaging or handling
• Lightstruck: skunk or rubber aroma, caused by a reaction between blue light and hop-bittering compounds
• Infection: vinegar or rotten aroma, caused by unwanted bacteria making its way into the beer

The role of volatile chemicals in aroma detection

The sense of aroma is perhaps the most powerful of the five senses. Aroma detection involves specific sensory receptors in the nose being stimulated by volatile chemicals in the air we breathe. The volatile chemicals in beer are released from the liquid or gaseous state and are characterised by a low molecular weight.

The two types of sensory organs in the nasal cavity are the trigeminal nerves and the sensory receptors. The trigeminal nerves are located at the entrance of the nose and are stimulated by physical stimuli such as cold air and high concentrations of carbon dioxide. The sensory receptors, on the other hand, are located at the top of the nasal cavity and are stimulated by specific aroma molecules.

The volatile chemicals in beer can be classified into two groups: major and minor beer aromas. Major beer aromas are present at levels greater than twice their threshold level, the level at which most humans can detect them. These include fruit aromas, floral elements, sulfur-based compounds, volatile hop aromatics, and fusel alcohols. Minor beer aromas, on the other hand, will be less distinct, but low levels of two or more aromas can act synergistically to create a combination aroma.

The detection of aroma involves more than just breathing while drinking. Coating the glass surface with beer allows a thin film of beer to evaporate into the air, making the aromatic molecules available to the olfactory receptors.

The process of brewing beer can result in the production of volatile chemicals that contribute to the aroma of the final product. For example, diacetyl, which is produced by all yeasts during fermentation, can give beer a buttery taste and smell. Another example is dimethyl sulfide, which can give beer a sweet corn or cooked cabbage flavour.

How to accentuate the aroma of a beer

The aroma of beer is exceedingly important, especially for full-flavoured beer. Here are some tips on how to accentuate the aroma of a beer:

Swirl the beer before smelling

Coating the glass surface with beer allows a thin film to evaporate into the air, making the aromatic molecules available to your olfactory receptors.

Breathe deeply and bring the air up into the top of your nose

A few sharp sniffs give a better assessment than one long snort. Also, note the aroma generated as you swallow—this arises retronasally from the back of the nose and can provide a more sensitive detection where less concentrated aromas become more evident in the aerosol generated by swallowing.

Use the right glassware

The shape of the glass can also affect the aroma. For example, a tulip glass or a snifter can help concentrate the aroma.

Store and serve at the right temperature

Low temperature and carbonation in beer will stimulate the trigeminal receptors, while hop, fruit, and alcohol aromas, among others, will stimulate the sensory receptors.

Pair with food

Pairing beer with food can also accentuate its aroma. For example, a beer with citrusy notes may be enhanced when paired with a citrusy dessert.

Choose the right yeast

The type of yeast used during fermentation can affect the aroma of the beer. For example, using a yeast that produces more esters will result in a fruitier beer.

Dry-hopping

Dry-hopping, or adding hops after fermentation, can also enhance the aroma of the beer by adding more hoppy notes.

Age the beer

Ageing a beer can help to accentuate certain aromas and decrease others. For example, ageing a beer with a high level of isoamyl acetate (which smells like bananas) will decrease the ester and result in a less fruity beer.

Use fresh ingredients

Using fresh, high-quality ingredients can also help to accentuate the aroma of a beer. This includes using fresh hops, grains, and yeast.

Control fermentation temperature

The fermentation temperature can affect the aroma of the beer. For example, higher temperatures will cause the production of more esters, resulting in a fruitier beer.

Avoid contamination

Contamination by wild yeast or bacteria can introduce off-flavours and affect the aroma of the beer. Therefore, it is important to practice good sanitation and brewing practices to avoid contamination.

Package carefully

How the beer is packaged can also affect its aroma. For example, using clear or green glass bottles can result in lightstruck beer, which has a skunky aroma. Instead, package the beer in kegs or brown bottles, which filter out more light.

The difference between ale and lager yeast

The aroma from beer brewing is not inherently bad for you, but it can be unpleasant or indicative of an off-flavour. Off-flavours are considered "off" or faulty when found at a certain level (or any level) in beer. However, the aroma of beer is exceedingly important, and it can greatly influence the drinking experience.

Now, onto the differences between ale and lager yeast:

The two main types of brewer's yeast are ale yeast and lager yeast. The type of yeast and fermentation technique used determine whether a beer is an ale or a lager. Ale yeast, or *Saccharomyces cerevisiae*, is a top-fermenting yeast that works best at warm temperatures of 60–75°F (16–24°C), with some strains requiring temperatures as high as 95–100°F (35–38°C). Ales can generally ferment and age within a short period, typically 3–5 weeks. Lager yeast, or *Saccharomyces pastorianus* (formerly known as *Saccharomyces uvarum*), is a bottom-fermenting yeast that works best at cold temperatures of 45–55°F (7–13°C). Lagers take much longer to ferment, typically up to 6 to 8 weeks.

Ale yeast is the same species of yeast used in baking bread, while lager yeast is a unique microbe that can metabolise complex sugars that ale yeast cannot. Ale yeast produces beer in as little as 7 days, making it more convenient for small breweries, whereas lager yeast requires more time and specific temperature conditions.

The choice of yeast significantly impacts the flavour and character of the beer. Ale yeast tends to produce more esters during warm fermentation, resulting in a stronger aroma. Lager yeast, on the other hand, thrives in cold temperatures and produces a mellow taste with lower alcohol content.

In summary, the fundamental difference between ale and lager yeast lies in their species, optimal temperature ranges, fermentation process, and the resulting flavour profiles of the beer.

How to avoid common off-flavours

The aroma from beer brewing is not inherently bad for you, but it can indicate the presence of off-flavours that may make the beer unpleasant to drink. Here are some tips to avoid common off-flavours in your home-brewed beer:

Diacetyl (Buttery/Butterscotch Aroma)

Diacetyl is often described as giving a buttery or butterscotch aroma to beer and is considered an off-flavour in most lager beers. To avoid this, make sure to boil your mixture vigorously for the appropriate amount of time. Aerate your fermentation well when you cast your yeast, and avoid oxygenating the wort further once fermentation has begun. Towards the end of fermentation, slightly increase the temperature to help the yeast reabsorb diacetyl.

Mercaptan (Rotten Vegetables/Sulphury Aroma)

Mercaptan will give your beer an aroma reminiscent of rotten vegetables, drains, or rotting garbage. This off-flavour is usually caused by certain yeast strains during fermentation or yeast autolysis. To avoid this, practice good sanitation and siphon your beer off the yeast within four weeks of starting fermentation.

Lightstruck (Skunky/Sunstruck Aroma)

Lightstruck is caused by a chemical reaction between daylight or artificial light, riboflavin in the beer, and hop alpha acids. To avoid this off-flavour, store and drink your beer away from direct sunlight and use brown bottles for packaging instead of clear or green glass, which lets in more light.

Hydrogen Sulphide (Rotten Eggs/Sewer Aroma)

Hydrogen sulphide will give your beer a distinct rotten egg or sewer aroma. This is produced by yeast during fermentation, especially when the yeast is stressed. To avoid this off-flavour, give your beer enough time to ferment, and select a yeast strain that suits your brewing conditions. Ensure you cast enough healthy yeast and oxygenate the wort well.

Dimethyl Sulfide (Sweet Corn/Cabbage Aroma)

Dimethyl Sulfide (DMS) will give your beer a sweet corn, cabbage, or cooked vegetable aroma. This is caused by a sulfur-based compound produced when grain germinates during the malting process. To avoid this off-flavour, reduce the use of pilsner malts and lager malts, and avoid oversparging. DMS is volatile, so a vigorous boil for at least 60 minutes will help eliminate it.

Frequently asked questions