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The impact of water availability on Vitis vinifera L cv Tempranillo grape yields and juice composition over a 3 year period was studied. Grape juice composition during the different stages of berry growth was compared. The analytical data collected were used to investigate the relationships between some of the different components studied in these berries during the ripening period. The object was to determine whether the relationships could be used to derive mathematical equations for use as indicators of the changes taking place in the different parameters considered and thus of the optimum time for harvesting the grapes for a given wine-making process. Very similar equations were derived for this grape variety irrespective of the culture conditions (use or non-use of irrigation) or the different ripening conditions employed. A high degree of correlation between some of the components considered was observed. In any case, cause-and-effect relationships could only be established for certain of the parameter pairs considered (total acidity/pH, pH/potassium,°Brix/glucose fructose, total acidity/tartaric acid and malic acid). For other parameter pairs (berry weight/°Brix,°Brix/pH,°B rix/total acidity) the relationship found was attributable to accumulation and breakdown processes which took place concurrently or overlapped in time. In two cases only there was uncertainty as to whether the relationship observed between the parameters was a cause-and-effect relationship or whether the parameters were so closely related that they acted as mutually limiting factors (°Brix/ proline,°Brix/total anthocyanins).

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