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Quality and safety in fortified wines

The project concerns improving quality and safety in fortified wines via an integrated, low input approach to minimizing bacterial spoilage. The approach taken is threefold: to define the symptoms and epidemiology of spoilage; to develop and validate methods for the detection and monitoring of undesired microbial activity; to develop and validate low-input, process interventions for the protection of the products against undesired microbial activity. Results from preparation and bottling installations suggest that there is no general trend of contaminant foci as hygienic practices vary so widely. Ethanol tolerant lactic acid bacteria (LAB) have been, however, isolated from various sites and it appears that scenarios of contamination at the later stages of the production process are possible. In the case of sherry, fortification takes place to a level that allows the growth of a surface layer of an `essential' (to achieve wine style) yeast. Initial results suggest that LAB are not responsible for all acetogenic spoilage in sherry as ethanol tolerant lactobacilli were isolated from an equal number of spoiled and unspoiled barrels of sherry. The chemical 'making safe' of sweet fortified wines has been studied using Pineau as a model. Nisin and added tartaric acid had little or no effect on the initiation and progression of spoilage. C10 and C12 fatty acids inhibit the initiation and progression of spoilage when used individually at concentrations above 30 and 60 mg/L respectively. Likewise sulphur dioxide was efficient in the delaying of the onset of pre-spoilage alterations when included in concentrations of 20 mg/L; 40 and 60 mg/L additions completely inhibited onset of spoilage. C10 fatty acid and sulphur dioxide had a potent synergistic action in combination effecting a stability for more than a year.