Fruity. Citrussy. Mellow and chocolatey notes?

We're not talking wine or coffee here; we're talking beer. And given the rise of craft breweries and ever more sophisticated consumer palates, the subtleties and varieties of beer are becoming big business.

However, for craft brewers, quality control can incur high costs. Enticing aromas are essential to the development of a tasty beverage and getting them right requires skilled personnel and costly equipment.

This is all well and good for big commercial breweries, but what about those microbreweries that operate out of warehouses in the ex-industrial suburbs?

Well, now University of Melbourne researches from the Faculty of Veterinary and Agricultural Sciences and the Melbourne School of Engineering have developed a low cost and portable 'electronic-nose', or 'e-nose', that uses machine learning to quickly assess beer quality based on its aroma.

The device is portable, allowing brewers to use it for rapid and reliable quality assessment on the production line.

It also has the potential to be used to assess other food and beverages at all stages of production and has already been tested to detect smoke taint in wine.

Not-quite-right

The development of off-aromas or off-flavours in beers can occur particularly in breweries that don't use pasteurisation.

The partial sterilisation that comes through pasteurisation isn't necessary to guarantee the safety of beer as it is a fermented product, and the process can modify aromas.

But on the plus side pasteurisation can reduce the risk of aroma and flavours going 'off'.

With consumers demanding more novelty, brewers are responding by experimenting with different flavour profiles – milky stouts, cherry and honeycomb beers and even pickle.

In an increasingly innovative environment like this, it's important to develop methods that can assess aroma both during and after boiling (with the addition of hops) and fermentation.

Gas chromatography instruments that analyse the vapours given off by a compound can be used to do this, but it's costly, time-consuming and involves sending samples away for assessment.

In beer, the aroma alone is a fairly reliable indicator of quality.

This is due to the close link between our senses of smell and taste. But in a small brewery, there may only be one or two people (including the master brewer) who are adequately trained to do this – conducting aroma testing sessions for each batch.

The process can be imperfect and takes time, but it's also ultimately highly subjective.

New and emerging technologies are able to get around this. Sensors, robotics and machine learning have been brought together to reduce time spent assessing food quality while providing a less variable test.

"Our study shows that this technology can be used to assess quality in the field. It's a first for a genuinely portable device," says lead author Associate Professor Sigfredo Fuentes.

Associate Professor Fuentes and PhD candidate Claudia Gonzalez Viejo's research started with a University of Melbourne student project that involved using Lego to create a device to measure bubbles in drinks.

The level of bubbling is an important quality of drinks, with consumers preferring medium-sized bubbles in products like sparkling water and in the foam for beer.

"You can determine how much people will like a drink by the quality of the bubbles," says Associate Professor Fuentes. "Bubbles and foamability and the stability of the bubbles are really important."

In beer, the froth or foam created by bubbles helps to protect the drink from oxidisation that alters the flavour profile – this is why dark stouts like Guinness are often pumped with nitrogen to create a fine foam on top to protect it.

"If you have a flat Guinness, it will oxidise, giving you off-flavours in five minutes," says Associate Professor Fuentes.

Measuring the bubbles and carbon dioxide led nicely into the next phase of Associate Professor Fuente's research – adding additional sensors to measure other gases and determine how those bring about different aromas.

Flavour profiles

To investigate the effectiveness of the e-nose, the researchers conducted a study of 20 different commercial beer samples, covering a range of styles and fermentation types.

The variety in beer styles helped create a computer program that can detect different volatile compounds, reducing bias in the artificial intelligence software that was developed alongside the e-nose, which was built by Bryce Widdicombe and Dr Ranjith R Unnithan at the Melbourne School of Engineering.

The e-nose – a small circuit board with a diameter of 92 millimetres – is placed face-down over a sample of beer in a beaker. The sensors can then measure the gases above the beer.

This data is measured in real-time, with the help of food technologist Amruta Godbole from the Faculty of Veterinary and Agricultural Sciences.

The results were measured against a traditional sensory session conducted by twelve trained panellists.

The panel assessed the intensity of different beer aromas – hops, spicy, floral, fruity, burnt sugar, grains, yeast, nut and carbonation mouthfeel. The samples were also measured using gas chromatography-mass spectroscopy (GC-MS).

One of the objectives is to also use the data from the e-nose to aid in the creation of flavour profiles.

"With the e-nose, you just do a pour, and then you get all the data through the machine learning – you get the whole aroma profile of the beer with 97 percent accuracy," says Associate Professor Fuentes.

The e-nose measures the peak area of different gases that are present in beer vapours before fermentation and afterwards.

The sensors on the e-nose are calibrated to measure the presence of gases like carbon dioxide, ethanol, methane, hydrogen, hydrogen sulfide, carbon monoxide, ammonia and benzene.

There are different gases present as a result of different types of fermentation, like lambic beers. These beers are produced by spontaneous fermentation using wild yeast. This allows for the development of more gases and aromatics than beers from top (like ales) and bottom (like lagers) fermentation that use domesticated yeast varieties.

A pint-sized product

The researchers hope to finesse the design further, making it smaller and integrating rechargeable batteries and WiFi to allow brewers greater flexibility, as the current version needs to be connected to power and a computer via USB.

But the potential applications of the device go beyond beer and identifying smoke taint to include building flavour profiles for sparkling wines and non-alcoholic beverages like coffee or tea.

"The e-nose helps take a good deal of subjectivity out of things," says Associate Professor Fuentes.

"Manufacturers will be able to definitively say what is in each flavour profile and put that information on the product labelling."

But will the e-nose replace a master brewer's taste?

Absolutely not says Associate Professor Fuentes. "I find that brewers are not against technology. They embrace it."

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