In ferment

British cider makers, despite claiming less than 5% of the UK's alcoholic drinks market, see over 1000 million pints of their product sunk every year.

Yet the process of maturation, in which microbes are used to turn the acidic raw material into a flavoursome drink, is traditionally time-consuming and expensive. Now, Dr. Robert Lovitt and Dr. Meirion Jones of the University of Wales, Swansea have been studying how this process can be improved in a project funded by EPSRC.

As maturation can take up to three months, it's no wonder that firms such as HP Bulmer Drinks Ltd already use membrane bioreactors to try and speed up the process.

'The primary agents are lactic acid bacteria that catalyse a series of reactions that reduce acidity in the cider,' explains Dr Lovitt, 'these also produce subtle flavour changes associated with the metabolism of tannin-derived substances.'

Because these reactions take place in a highly alcoholic (up to 10% w/v) and highly acidic (pH 3.5) environment, the major challenge was to develop a process and find equipment that could withstand these harsh conditions. The overall aim is to create a faster maturation process by managing and intensifying the growth and metabolism of lactic acid bacteria.

The team's approach was to grow the cells in a more favourable environment first before introducing them to the cider. 'This avoids slow growth and poor yields encountered when starter cultures are used to inoculate cider and the expense of producing the starter culture itself,' says Dr. Lovitt: 'During the rapid maturation process the propagated culture only has to survive rather than produce good growth.'

So far, the new process has resulted in the intensive production of a wide range of lactic acid bacteria to commercially useful amounts (over 25-50g dry weight, typically 2-5g in standard batch culture).

'We are now gathering the data necessary to construct numerical models to enable the prediction and control of the propagation process,' says Dr. Lovitt.

According to Dr. Lovitt the project's industrial partners - HP Bulmer Drinks Ltd, Interprise Ltd and PCI-Memtech UK Ltd - have been able to see how bioprocess engineering can make their processes more profitable and reliable. The team also believe that their methods could be put to use elsewhere 'lactic acid fermentations often have an ethnic or regional use, for example in rice wines, soy sauce and starter cultures for dairy and vegetable fermentations,' comments Dr. Lovitt.

Currently halfway through the project, the researchers aim to move their equipment out of the lab and into the workplace at both Interprise and Bulmer for propagation and maturation trials. The next step is proving that their process is commercially viable.

'We will use green cider from primary fermentation as it is made at Bulmer to see what good quality cider we can make and how it compares with other maturation processes,' says Dr. Lovitt, 'we hope to shorten the production cycle from several weeks to less than one week and demonstrate how robust and versatile our process is.'

If other industries are to follow the cider makers' example and develop innovative new processes Dr. Lovitt is convinced that a thriving community of biochemical engineers is needed. He believes that to exploit world-class basic research in this area more researchers have to be 'working at the boundaries between the applied world of engineering and fundamentals of underlying biological processes.'