As part of Brewlab's involvement in theGreat Brettamomyces Megablend 2017, we have published 2 reports by our director; Dr ...
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22nd Nov 2017 by Richard
Which part of a brewer’s body is constantly working? Even the brain has a tea break and the eyes automatically close when sleep arrives. The tongue only works when beer is sipped and the ears only respond when pumps whirr or the phone rings. Muscles relax too, both in response to the end of work pint and the end of day pillow.
Meanwhile the nose continually responds to the environment providing information on the brewing process or, hopefully, awakening the sleeping body if the house fills with smoke.
Cross section of the human nose.
Much of this is unconscious, only alerting the brewer when conditions require attention. Few brewers though have not experienced a moment of anxiety when an undesirable aroma is suddenly perceived on a tour of the brewery or wafting into the brewery office. Stale malt by the mill, a phenolic tang in the fermentation room or a burning aluminium from an overheated pump.
In performing this function the nose is acting as the most basic animal sense, responding directly to chemicals constantly flowing into the body. Primitive animals such as amphibians and reptiles don’t have noses separate from their mouths just an oral cavity where taste and aroma receptors pass information directly to the brain.
Fortunately a brewer’s physiology is more advanced and benefits from a separate nasal cavity allowing perception of aroma at a distance. In assessment of a beer this is valuable and not only in keeping your food out of your nostrils. A particular advantage is the sensitivity of the system being enhanced by the large volume of air drawn into the lungs – 23,000 breaths per day containing over 400 cubic meters. Just try swallowing that volume to taste your beer.
What though is in a brewer’s nose? Shining a torch won’t show a great deal but more delicate investigations show that the nasal cavity contains a number of bony ridges to warm incoming air. In the upper part of the cavity are two areas of nerve receptors. One branch in the bridge of the nose, another at the very top of the cavity.
Those in the bridge of the nose are connected to the trigeminal nerve and respond to a limited number of chemicals, generally potentially hazardous ones such as carbon dioxide and to the impact of low temperature. The fizz from a mouthful of lemonade is enough to stimulate these and the sharp snap of burping a fizzy drink is a good example of the effect.
Capicinoid oils from chillies and mustard oils are two other materials active on the trigmenal nerves. While such stimulations may have their direct impression a secondary result is to reduce the sensitivity of the major aroma receptors. In effect the body concentrates on a potential hazard – high CO2, intense cold or chemical dangers. Meanwhile it forgoes the delights of hop character of complex esters. The fact that many beers are designed to maximise the impact of two of these features, CO2 and low temperature, has inevetable implications on overall flavour character.
Under less challenging conditions the nose uses the main aroma receptors to detect specific chemicals. Four million of these receptors reside in the nasal cavity. Many less than the 200 million in a bloodhound but enough to fire up when exposed to a hoppy pint of beer. Similarly, compared to the tongue the range of responses covers a forest of flavour rather than a handful of tastes. Many thousands of aroma chemicals may produce a response here giving a widely expanded impression of the world.
The process of response may be similar to the tongue with aroma molecules fitting into receptors of specific shapes on the receptor cells. Once an aroma flavour fits into a receptor the cell generates an electrical impulse. If enough cells do this they may stimulate a nerve cell which will conduct an impulse to the brain. Only eight molecules may be needed to stimulate a cell and although forty cells may be required for the brain to perceive the aroma the total number of molecules is relatively few.
This doesn’t mean that the nose responds to every aroma. Some are much more evident than others. For example we are most sensitive to the smell of burning hair, and rightly so. Our response to ethanol is very much less, requiring a concentration of around 4% before we stand much chance of recognition.
Diacetyl and 2,3 butane diol are two other examples with very different thresholds. The ease with which one is converted into the other and alters beer flavour during maturation indicates how rapidly a beer may change its character.
Although the nose responds most directly to aromas from a distant source it is equally active during the swallowing of beer. When beer reaches the back of the mouth it is agitated and warmed. Less volatile aromas are released and spray up into the back of the nose. Perception of certain aromas is best made at this point so concentrate hard as you swallow. The nose responds to such aromas at the same time as the tongue is savouring tastes. Interaction of responses between nose and mouth doubtless occurs in the brain resulting in a synergy of flavour.
This response does not end once the beer is swallowed, as flavours will persist in the body for some time circulating in the blood stream. Experiments have even measured the release of odour molecules back into the nasal cavity from the blood so causing an after drink appreciation. The possibility of this aiding digestion or encouraging further intake is an unexplored area.
A similar effect is possible from tasteless foods and materials. Drug tablets for example, are typically swallowed whole and not tasted. Contamination or poor choice of coating materials may lead to flavours appearing in the blood and causing nausea when released into the nose. The same may be possible of foods which are swallowed rapidly or which react with stomach acids to release flavour active compounds. The production of sulphur dioxide is one example of this and can lead to allergic reactions in sensitive individuals if enough gas burps out into the lungs.
Changes in aroma may also occur when some compounds are diluted. Mercaptan aromas can be examples of a beer flavour showing this feature. Animal scent glands are others. Many of the latter are repulsive when met raw but revered when diluted in perfume. Fortunately these aromas can now be manufactured synthetically but it does beg the speculation of how the attraction of diluted animal excrescence was ever discovered.
Keeping a healthy nose is essential to your sensory evaluation programme. This is more than just the use of a tissue when you sneeze but a conscious awareness of minimising nasal stress. Physiologists are aware that the human nose is poorly designed for air flow. A tight hairpin bend at the top of the cavity slows air movements and limits the nose’s use during the heavy breathing of exercise. As soon as you start running or chasing a squash ball the mouth falls open allowing air a direct run into the lungs.
Many other animals have a more direct nasal route. Animals such as snakes, pigs and squirrels, which operate close to the ground, have the greatest nasal capacity per body size. Our own convolutions seem to have resulted from the expansion of our brain and, possibly, as a means of filtering particles from incoming air. The presence of nasal hairs helps this and soon accumulate a nose full of dirt and dust. Naturally this can block the perception of aromas so limiting your response.
For a tasting panel this means that your members may differ according to their environment at home, their activities at work and any recent exposures to dust and particles. Industrial regulations now control and limit working environments but enthusiastic home renovations can create equally poor effects. One brewery avoids critical tasting sessions on a Monday to minimise the effects of weekend activities.
Occasional exposures to irritants will produce temporary effects. Continual exposure may permanently disable. Staff at a 1960’s tyre factory in the UK were continually exposed to solvents for remoulding rubber. Not did they become addicted to the solvent but lost all trace of aroma recognition. Living in urban environments may perform less extreme effects, but could make standardisation of taste panels difficult. Regular, chronic exposure to solvents, perhaps as encountered in laboratories may achieve a similar effect.
Mucus is the key to nasal regeneration as it flows across the nasal receptors wiping the area for fresh stimulation. As with taste the nose is affected by illness. A heavy bout of cold severely reduces aroma perception, possibly because of the increase in mucus flow but also be distracting the brain’s response to the stimulation.
More serious diseases can be accompanied by an odour on the breath, most probably due to metabolic changes in the body. Ketones indicate diabetes. Typhus is associated with the smell of mice, plague with mellow apples, yellow fever with butchering and nephritis with ammonia. The effect of these on flavour perception is unknown but the appearance of any in your tasting panel would be cause for concern.
That said sensitivity isn’t always the most critical requirement of a tasting panel. In some cases it is the ability to judge the overall character of a beer against standards and criteria. Is today’s brew up to scratch? Which sample is the odd one out? How does a new brew compare to last weeks or with the same beer from a different brewery? Or even more difficult - which is the best beer of the competition?
Flavour perception is most competently applied in middle age when experience provides the context and comparabilities to judge a complex sample. In contrast sensitivity is most acute in pre pubescent girls – not a group we would use to fill a beer tasting panel.
Maturity and experience are valuable attributes, both of which involve memory of beers, flavours and associated features. Developing a flavour memory enhances your ability to recognise and identify flavours. However, for technical work it is important to ensure that flavour memory is associated with agreed reference standards1. For example in the recognition of stale characteristics it is important to refer to underlying chemicals such as trans 2 nonenal rather than the more evocative but vague terms “cardboard” or “wet clothes”.
The list of reference terms and compounds detailed by the Joint Working Groups of the EBC, ASBC and MBAA2 provides the basis for international standardisation and should be used in training to ensure that comparable impressions are obtained by different panels. Repetitive exposure is necessary to develop an appropriate and accurate flavour memory – in much the same way as regular conversation will improve your French.
Taste memory has a further, less quantifiable, dimension in the evocation of personal emotions and memories. Literature contains numerous instances of such evocations as a means to recall events. Personal experiences can often be recalled by a particular smell.
Can beer stimulate emotions by recall? Many synthetic flavours are used to promote sales of specific products. In fact only 20% of the perfume industry’s output is sold as personal perfume. 80% is used in providing aromas to variously unpleasant or neutrally smelling materials, from toilet paper to bin sacks. Magazines may be impregnated with aromas for particular advertisements while potentially offensive plastic or rubber materials may be infused with more attractive aromas than those naturally arising from their chemical origin.
Perfumes are also used in targeted sales promotions as aerosols in shopping areas and may be included in CD’s for release on playing. How the underlying aroma of stale bar carpets affects our drinking associations may be a project worth exploring.
Old beer will certainly find difficulties in matching public aroma expectations. However, freshly pulled beer does carry a wealth of fruit and hop aromas which tend to have positive associations. Some of this will results from appropriate marketing to the beer drinking public but the association of beer with pleasurable experiences is continually encouraged and reinforced. In some cases this may be neutralised by other associations and the amnesiac effect of drink itself. Perhaps an expansion of beer flavours into other products would expand this association and produce a more persistent effect. Beer flavoured chocolates, tyres and tissues may be just the stimulus the industry needs.
Simpson, W. A Rough Guide to Beer Flavour Assessment. Brewers' Guardian. September 1997.
Meilgaard, M.C. Dalgliesh, C. E and Clapperton, J. F. Beer Flavour Terminology. Journal of the Institute of Brewing. Vol 85. 38-42.