The cider sector has undergone considerable changes over the last few years. With technological advances, the traditional, at times conservative, methods have experienced great changes. New systems have been introduced into the tolares (the cider-making plants), incorporating the continuous washing of the apples, new types of pressing and polyester-coated stainless steel recipients, refrigeration, etc. Also the idea that certain cultural concepts based on concrete observations often need scientific confirmation has also evolved, enabling the adaptation and diversification of traditional procedures while maintaining the quality of the cider at all times.
The criteria for evaluating a product have to be defined and assessed taking the nature of the product into account. In the case of cider, the intrinsic value of the raw material – apples – is the foremost element of this quality. A second group of factors include a number of different, generally spontaneous reactions, favourable or otherwise, that are produced after the picking of the apples, influenced by the ripeness of the fruit and hygiene conditions when handling. Finally, the changes that may be produced in the cider, as a function of the conditions and duration of storage, have to be understood and taken into account.
The aim of the work taken up in this Report is to contribute to the enhancement of knowledge about the factors that affect the quality of cider produced in the Basque Country. The analytical techniques used are the usual ones in this foodstuffs field: enzymatic and liquid-liquid and gas-liquid chromatography. New analytical applications of a more recent technique have also been developed: high-resolution nuclear magnetic resonance (NMR) spectroscopy.
In the NMR spectra of the proton of the apple juices, the principal resonance signals corresponding to phenolic compounds appear in the area of low magnetic resonance field. In this area peaks appear that correspond to chlorogenic acid and to (-)-epicatequine that can be used for their determination. Simple and rapid analytical methods have been developed from these signals and, requiring a minimum preparation of the sample to enable determination of chlorogenic acid and (-)-epicatequine in cider apple juices.
The analytical and chemometric characterisation of six varieties of cider apples from different orchards in Gipuzkoa (the Basque Country) was undertaken. In this analytical study the usual analysis techniques of NMR spectroscopy have been used and compared. This spectroscopy, used in conjunction with chemometric techniques, provides positive advantages in the characterisation of foodstuffs, particularly its speed and minimum handling of the sample.
Given the importance of the right choice of apples to obtain mixtures that provide a balanced apple must, the analytical characterisation of 27 varieties of cider apples was carried out, determining general parameters and acidity and sugar profiles throughout the 2000, 2001 and 2002 seasons.
Experimental design and factorial analysis were used to determine the influence of new alternative technologies (type of press and the material of the fermentation tank) on the general parameters of glycerol and volatile and acidic compounds of both fermenting apple must and of the cider obtained. Once bottled, their progress was monitored over a seven-month period.
Finally, the influence of various mixtures of apple varieties on the initial composition of the musts and their evolution during fermentation to cider was studied.
The research centred on the progress of malolactic fermentation, which occurs at different relative rates with respect to alcoholic fermentation in the different musts, thus affecting the characteristics of the ciders obtained.