Taste by Numbers - blog post by Brew By Numbers… | Brew By Numbers

Taste By Numbers

Your sense of taste and smell is amazing. You can detect down to 1 molecule in 2 billion! It’s the result of a long and intricate evolutionary process - a process that started millions of years ago to help guide us towards good and nudge us away bad stuff in our environment. This process has left us with the ability to detect over 10,000 different molecules through smell and taste, making the wide variety of flavours that craft beer has to offer really exciting. So how did it all happen?

Evolution and Taste

10 million years ago the inquisitive early apes would put things in their mouths, hoping that these things might be a good source of nutrients, although they could just as easily be harmful. The ones that were unable to detect certain flavours might have gotten ill and even died. Others, with better chemoreception (the technical term for our sense of taste and smell) would be able to avoid these substances and survive to breed again. Because of this, our sense of taste and smell became a fundamental feature of our survival tool kit. Evidence of this can be seen in how our sensitivity to different molecules reflects their importance to our health. A great example is our sensitivity to hydrogen sulphide (sewage, rotten eggs) which we can detect down to 1 molecule in a billion!

La Monkey
La Monkey

Our Basic Senses of Taste

Bitterness became very important as a warning system: our tongue letting us know that a plant might be harmful to us. Of the 40 different taste receptors in our mouth, over half identify bitterness. Interestingly, as we age, our perception of bitterness diminishes from when we were children. This could be as these foods become less harmful as we grow.

Sweetness works the other way. Out on the plains of the Serengeti, early humans relied on sweetness to indicate high nutritional value. Hijacking this mechanism in insects, yeasts can produce sweet, fruity esters like Ethyl 4-methyl-pentanoate as a way to attract them and be carried away elsewhere.

Our sense of Sourness comes from the need to to detect H+ (positively charged hydrogen ions)

the same way as pH meters. This was important to determine the ripeness of fruit, and as an indicator of spoilt food - normally caused by harmful bacteria. Our sensation of acidity is pretty much instant, so as to prevent us from swallowing harmful things. One way to see this in action is to watch someone drinking a Gueuze (a Belgian sour beer, which has a pH range of 3.20 - 3.51) for the first time. Watch the reaction on their face... It’s really quite sour!

Sour beers
Sour beers

Kraft Life

Our appreciation for craft beer develops with our ability to tap into these ancient evolutionary systems and detect a wide variety of complex flavour and aroma compounds. It can of course also be a hindrance!

At BBNo, it is essential for our brewers is to ensure excellent cleaning practices. As with our ancestors we are all highly sensitive to various off-flavours, and in beer that indicates infections or other problems with fermentation or processing. Below the detectable level, these flavours can reduce the definition of the beer, making it hard to discern the intended flavours.

Beer judges are particularly good at detecting certain ‘off-flavour’ compounds like Diacetyl (buttery popcorn, butterscotch). This smell is normally a sign of yeast stress or mutation and is generally considered a fault across most beer styles. Beer judges have been shown to be able to identify it down to 10 particles in a million!

Each sip of beer (around 20ml) contains 6.022 x 10^23 total molecules*. Of these, there only needs to be 4 million molecules of 3-methyl-2-butene-1-thiol for humans to detect it as a skunky, rubbery flavour. That’s only 1 molecule per 2 billion (or 0.5 ppb)!


Another example is Dimethyl Sulphate, or DMS, (corn, cabbage, vegetal) that can be detected as low as 30ppb. This is normally the result of problems in the brewhouse, with larger amounts indicating infection.

Ethyl Acetate is another flavour compound produced during fermentation in both larger and ales. By varying it just a few %, it changes our perception drastically. At low levels, below 100 parts per billion, its perceived as a pleasant fruitiness. However, above 100ppb it tastes more like nail polish or solvents. Going back to evolution, our ability to detect the high levels of Ethyl Acetate would have helped us to determine the fruit we found was too rotten to eat.

Fermentation temperatures are also critically important in the development of these flavours, as yeast are highly sensitive to slight changes. During the early stages of fermentation (24-48 hours) a variation of 1 - 2°C in temperature can alter the balance of fruity esters and spicy phenols in the beer. This is especially noticeable in wheat beer styles, where these compounds provide the main flavour characteristics of the style.


Of course, as is the case with those wheat beers, not all of these strange compounds are undesirable.

Here are a couple of good ones to try to detect in our beer:

31|Hefeweizen - Isoamyl Acetate (banana). Detection threshold: 1.2ppm.

Produced by yeast and normally found certain european styles of wheat beers. Also, found in high-alcohol beers from yeast stress. Imperial Banana Stout anyone?! Hefferveisen can also contain 4-vinyl guaiacol (clove, phenolic) detectable at 1ppb.

18|Farmhouse - 4-ethyl phenol (barnyard, horse blanket). Detection threshold: 400ppb.

Commonly found in beers containing brettanomyces wild yeast. Interestingly, it’s association with horse blankets is less complex than one might think. It’s just one of the yeast’s favourite environments! Horse blankets smell like this because of a large brett population.

TBNO 18 31
TBNO 18 31


All of us have the ability to taste a spectacular variety of different flavour molecules through the 40 known taste receptors in our mouth. The thing that separates most of us from professional tasters is the ability to identify and describe these elements. By practicing to identify these different flavour compounds by trying a wide range of beers, you can help to widen you sensory vocabulary, and further you enjoyment of craft beers… Cheers!


Written by: Tom Hutchings, Co-Founder & Managing Director
Photo Credits:
Robert Mathews, Mathew Schwartz, Dan Hogston.


Tasting Beer by Randy Mosher - https://randymosher.com/Tasting-Beer

*Calculations for a beer with a gravity of 1.010. Assuming density is about 10% higher than water (18 mg) at 20 mg.
Number of moles in 20 ml of beer = 20ml /20 g/mol = 1.
Number of molecules in 20ml of beer = number of moles (1) × Avogadro's number (1×6.022 × 10^23) = 6.022 x 10^23