Brewing up a storm

Expertise is priceless. It's also limited. This is becoming an increasing problem for the brewing and distilling industries.

Like many parts of the food industry, the centuries of tradition which underlie the processes are beginning to weigh against the operators; if the quality of a product relies heavily on the expertise of one or two craftsmen, then the future of the company is also in their hands.

And as in so many other areas, the era of the craftsman is, sadly, coming to an end. But as the cliché says, a problem is often an opportunity, and process engineering researchers are currently looking for new ways to bring modern technology into the process while preserving the character of the product.

The roasting of barley and malt (the term for barley once the seeds have begun to germinate) is one such area. Roasted malt and barley are vital components of the various types of beer brewed in the UK; the malt provides flavour, providing distinctive flavours and colours to the beers.

The roasting process hasn't changed for centuries; the roasters, similar to those used to roast coffee, are controlled by experienced maltsters who judge the roasting time and conditions by examining the malt and barley before and during the roasting by hand and eye. The degree of expertise here is considerable; most maltsters can achieve a 90 per cent success rate for colour. But the experienced operators are approaching retirement age, and as with so many other traditional crafts, there isn't a generation of apprentices in waiting to take over.

Enter new technology. A LINK scheme, bringing together academia and industry, is currently hard at work to devise new ways of monitoring and controlling the roasting process. It may seem a simple task, but the processes are turning out to be among the most complex tackled in food processing.

The project is aiming to allow brewers to specify not only the colours, but also the flavour profiles of the roasted malt and barley. This is currently not possible, but it has been something that breweries are keen to achieve.

Monitor duty

The LINK consortium, coordinated by Catherine O'Shaughnessy of Brewing Research International, is now coming to grips with the implications of their targets. Monitoring the process via the development of colour is not practical for a fully-automated process because the changes in colour are not uniform.

It generally takes two hours to roast barley, but most of the colour and flavour development takes place at the end of this period, when all the water has been driven off. In the last 20 minutes, the colour value may increase from 200 units to 1500 units; in the last two minutes, it can rise from 1000 to 1500. It takes only 30 seconds for the darkest grades of malt to char if left in the oven.

Because of this, even on-line colour monitoring would not provide fine enough control for the process. Simple feedback control, using parameters such as humidity and temperature, is also likely to be impossible. The only option is to come to an understanding of the processes taking place inside the barley and malt grains themselves, as the conditions in the oven work to develop the flavour, and then devise a control strategy based on this processes.

Colour development procedes by a variety of mechanisms. The two simplest are pyrolysis, which is the major mechanism that browns toast; and caramelisation, caused by the action of heat on sugars. But the most important one for the development of flavour is the Maillard reaction — the interaction of reducing sugars, such as glucose and sucrose, with amino acids and proteins. It's a complex process, involving a cascade of reaction and a wide variety of intermediates. If the team are going to develop a way of specifying flavour, they will have to come to grips with the Maillard reaction, and the way it procedes inside a barley grain.

The Maillard chemistry experts at the University of Leeds' food science department are bringing their knowledge to bear on the problem, combining with Simpson's Malt's full-scale roaster and BRI's pilot-scale roasting equipment and sensory research. These results feed into further development at Omron, where Colin Bravington is leading a project to develop a fuzzy logic system to control the process. Meanwhile, Prof Peter Fryer of the University of Birmingham's chemical engineering school, along with PhD student Phil Robbins, are applying their expertise to an unusual problem — modelling the mass transfer and chemistry within each individual grain.

Looking deeper

The researchers are applying heavyweight techniques to the problem. For example, the Birmingham team is using magnetic resonance imaging to follow the flows of moisture inside the grains, and positron emission particle tracking to study the movement of grains inside the roaster. This will help them understand the heat and mass transfer processing for the individual grains, and will allow them to incorporate process chemistry to the model.

'The first intention is to increase understanding of the process and to use this understanding to build a better control system for the existing process,' comments Fryer. To do this, the team is using a test-rig incorporating a fluidised bed roaster, rather than the rotating drum roasters more common in the industry. This is because fluidised beds are well understood and comparatively easy to work with, on a theoretical and practical basis, while rotating drums present several difficulties. 'It may be that we show that fluid beds have some advantages as a process,' says Fryer, 'but the aim of the project is not to replace the existing kit.'

The high-tech monitoring techniques, although looking at different scales of the process, are 'very compatible,' Fryer says. 'One shows how diffusional processes operate within single grains, whilst another shows how the grains behave within the roasting environment. As such, they can be connected very readily in terms of predicting the conditions within the grain during roasting.' This, he says, will help them develop a process model which works on both the macro and micro scales.

The Leeds team, meanwhile, is looking at the chemistry itself. Maillard reactionns are complex, proceding through a variety of intermediates. Prof Bronek Wedzicha, who has previously researched the kinetics of food browning due to dehydration and the use of radio-labelled glucose to follow the development of flavour compounds in cereals, is acting as a consultant on the project, to determine the best way to monitor the chemical progress of flavour development, so this can be related back to the physical conditions.

The results from these projects, and from other parts of the consortium, will then help Omron to develop a fuzzy logic model which relates flavour formation to process conditions and time. This will be based partly on the flavour compound study from Leeds, and on empirical experiments, which will be conducted with the help of a taste profiling panel from BRI and Pure Malt Products, a company specialising in extracting flavour and colour compounds. The panel will taste various roasted malt and barley samples, and characterise the flavour in terms of a set number of 'descriptors' such as malty, toffee, caramel, nutty, roast and bitter, and grade them in terms of intensity, to decide the correct end-point of the process.

Fuzzy logic

The project will come together with the development of an overall control regime for the roasters. This is where fuzzy logic becomes important. This technique is useful in modelling processes which normally depend on human intuition. It can handle variations in feed quality and the different thresholds set for various flavour chemicals by the taste panels; moreover, it can be easily modified by companies to take account of different types of equipment, and the varying requirements of clients.

However, even the fuzzy logic system is not sufficient to provide control of the process. The researchers expect that they will have to incorporate on-line analysis of off-air temperature and humidity to control inlet conditions, and an off-line 'trimming' of the conditions halfway through the process, based on the progress of the process using a measurement such as grain colour.

'This may need to be made at one or more points during the roasting process to facilitate the most accurate prediction of when to stop the process,' they say.