Fernanda Cosme

Optimization of honey-must preparation and alcoholic fermentation by Saccharomyces cerevisiae for mead production.

Mead fermentation is a time-consuming process, often taking several months to complete. Despite of the use of starter cultures several problems still persist such as lack of uniformity of the final products, slow or premature fermentation arrest and the production of off-flavors by yeast. Thus the aim of this study was to optimize mead production through the use of an appropriate honey-must formulation to improve yeast performance alcoholic fermentation and thereby obtain a high quality product. Honey-must was centrifuged to reduce insoluble solids, pasteurized at 65°C for 10 min, and then subjected to different conditions: nitrogen supplementation and addition of organic acids. Although the addition of diammonium phosphate (DAP) reduced fermentation length, it did not guarantee the completeness of the fermentation process, suggesting that other factors could account for the reduced yeast activity in honey-must fermentations. Sixteen yeast-derived aroma compounds which contribute to the sensorial quality of mead were identified and quantified. Global analysis of aromatic profiles revealed that the total concentration of aroma compounds in meads was higher in those fermentations where DAP was added. A positive correlation between nitrogen availability and the levels of ethyl and acetate esters, associated to the fruity character of fermented beverages, was observed whereas the presence of potassium tartrate and malic acid decreased, in general, their concentration. This study provides very useful information that can be used for improving mead quality.

Comparison between different types of carboxylmethylcellulose and other oenological additives used for white wine tartaric stabilization

Carboxylmethylcellulose (CMC) is authorised to prevent wine tartaric instability. The effect of CMC structural characteristics on their effectiveness is not well understood. The main purpose of this study was to compare the impact of CMCs with different degrees of substitution and molecular weight, on tartaric stability, tartaric acid, mineral concentration, phenolic compounds, chromatic and sensory characteristics in white wines, and compare its effectiveness with other oenological additives. Mini-contact test showed that all CMCs and metatartaric acid stabilized the wines; however, some arabic gums and mannoproteins do not stabilized the wines. CMCs had no significant effect on tartaric acid, potassium, calcium and sensory attributes. Tartaric stabilization effectiveness depends on CMCs degree of substitution, but also on wine matrix, probably its initial potassium content. Results suggest that CMC is a good alternative to white wine tartaric stabilization; nevertheless deeper structure knowledge is necessary in order to choose the appropriate CMC for a given tartaric instability.

General phenolic characterisation, individual anthocyanin and antioxidant capacity of matured red wines from two Portuguese Appellations of Origins

BACKGROUND The main aim of this work was to evaluate the general phenolic composition, individual anthocyanin content and total antioxidant capacity from 20 commercial matured red wine samples (vintage from 2005 to 2008) produced in two Appellations of Origin from the north of Portugal: Douro and Dão. RESULTS The results showed that the levels of general phenolic compounds, individual anthocyanins and antioxidant capacity in the 20 matured red wine samples analysed differed significantly. In addition, matured red wine samples aged in oak wood had a lower total individual anthocyanin content (from 13.85 to 56.79 mg L(-1), averaging 46.13 mg L(-1)) than wines aged in bottle (from 25.93 to 252.82 mg L(-1), averaging 94.17 mg L(-1)). The total antioxidant capacity values of the analysed wines showed quantitative differences among the values obtained from each antioxidant method applied as well as differences in the range of variation, especially for the values obtained by the DPPH method. CONCLUSION The wines used in this study constitute quite a heterogeneous group, made from different Portuguese red grape varieties, with diverse ages and two ageing processes (bottle and oak wood barrels); and accordingly, they showed important differences, especially in their phenolic composition. Finally, the oak wood ageing process before bottling had a negative effect in individual anthocyanins content in contrast to matured red wines submitted only to a bottle ageing process.

A simple, cheap and reliable method for control of 4-ethylphenol and 4-ethylguaiacol in red wines. Screening of fining agents for reducing volatile phenols levels in red wines.

Brettanomyces/Dekkera produces 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) from hydroxycinnamic acids that affect the wine aroma and overall quality. A simple, cheap, fast and reliable quantitation method is needed for routine quality control of wines. In this work a simple method based on one simple liquid-liquid extraction with pentane/diethyl ether (2:1) and analysis by GC-MS allow to obtain very good recoveries (98-102%) and low quantification limits (24 and 11μg/L for 4-EP and 4-EG, respectively), well below the sensory threshold for these volatile phenols and with an adequate measurement uncertainty: 70, 1.75 and 78, 1.95 and 1.35μg/L for levels of 1000, 25μg/L for 4-EP and 1000, 25 and 10μg/L for 4-EG, respectively. In addition a screening of eight fining agents (mineral, protein and polysaccharide based) for reducing the levels of these volatile phenols in red wines was performed, and the impact on the physicochemical characteristics of red wines was evaluated. At the levels used, activated carbon was the most efficient fining agent in removing 4-ethylphenol and 4-ethylguaiacol from red wines (57%) resulting in a 75% decrease of headspace concentration of these volatile phenols. Lower reductions were observed when using egg albumin (19%) resulting in a 30% decrease in the headspace concentration. Other fining agents although not reducing the total amount of the volatile phenols present in wine decreased their concentrations in the headspace like isinglass (27%), carboxymethylcellulose (15%) and chitosan (27%). All of these fining agents could be a possibility for treating wine contaminated with 4-ethylphenol and 4-ethylguaiacol.

Origin of the Pinking Phenomenon of White Wines

Pinking is the terminology used for the salmon-red blush color that may appear in white wines produced exclusively from white grape varieties. The isolation of pinking compounds and their analysis by RP-HPLC-DAD and ESI-MS(n) showed that the origin of the pinking phenomenon in white wines from Vitis vinifera L. of Sı́ria grape variety are the anthocyanins, mainly malvidin-3-O-glucoside. The analysis showed that the anthocyanins were located both in the pulp and in the skin. Wine pinking severity was negatively related with the increase of the average temperature of the first 10 days of October, the final period of grape maturation. The minimum amount of anthocyanins needed for the pink color visualization in wine was 0.3 mg/L. The appearance of pinking in white wines after bottling is due to the lowering of free sulfur dioxide, which leads to an increase of the relative amount of the anthocyanins red flavylium form and their polymerization, resulting in the formation of colored compounds resistant to pH changes and sulfur dioxide bleaching.

Influence of the structural features of commercial mannoproteins in white wine protein stabilization and chemical and sensory properties

The cloudy aspect formed in white wines due to protein instability is a visual defect. Sodium bentonite is the most commonly used fining agent to treat this instability, but has usually a negative impact on the wines physicochemical and sensory characteristics. Aiming to find suitable alternatives, eleven commercial mannoproteins were chemically characterized concerning their sugar composition and protein content, and their effectiveness on wine protein stabilization. Also, their effect on the amount and nature of phenolic compounds, browning potential, chromatic and sensory characteristic was evaluated. Protein stabilization effectiveness was related to their chemical composition, namely their high mannose to glucose ratio. Additionally, some mannoproteins decreased the browning potential. Thus, mannoproteins could be an effective alternative for protein stabilization, preserving or even improving wine quality.

Reduction of 4-ethylphenol and 4-ethylguaiacol in red wine by activated carbons with different physicochemical characteristics: Impact on wine quality

Activated carbon (AC) could be a solution to remove 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) off-flavours from Dekkera/Brettanomyces contaminated red wines. The relation between AC physicochemical characteristics and removal efficiency of these compounds is unknown. The impact of ACs characteristics on 4-EP and 4-EG removal, phenolic and headspace aroma composition was studied. All ACs reduced significantly 4-EP and 4-EG levels (maximum 73%). Their efficiency was related to their surface area and micropores volume. A higher surface area of mesopores and total pore volume were detrimental for anthocyanins and colour intensity, while a higher surface area and micropores volume were important for removing phenolic acids. Volatile phenols reduction was more important for the positive fruity attribute perception than the abundance of headspace aroma compounds. With an optimal selection of the AC physicochemical characteristics it was possible to remove efficiently the volatile phenols without impacting negatively on the wine sensory quality.

Data on changes in red wine phenolic compounds, headspace aroma compounds and sensory profile after treatment of red wines with activated carbons with different physicochemical characteristics

Data in this article presents the changes on phenolic compounds, headspace aroma composition and sensory profile of a red wine spiked with 4-ethylphenol and 4-ethylguaiacol and treated with seven activated carbons with different physicochemical characteristics, namely surface area, micropore volume and mesopore volume (“Reduction of 4-ethylphenol and 4-ethylguaiacol in red wine by activated carbons with different physicochemical characteristics: impact on wine quality” Filipe-Ribeiro et al. (2017) [1]). Data on the physicochemical characteristics of the activated carbons are shown. Statistical data on the sensory expert panel consistency by General Procrustes Analysis is shown. Statistical data is also shown, which correlates the changes in chemical composition of red wines with the physicochemical characteristics of activated carbons used.

Volatile components of vine leaves from two Portuguese grape varieties (Vitis vinifera L.), Touriga Nacional and Tinta Roriz, analysed by solid-phase microextraction

The purpose of this work was to study the volatile composition of vine leaves and vine leaf infusion prepared from vine leaves collected at 30 and 60 days after grape harvest of two Vitis vinifera L. species. Eighteen volatile compounds were identified by gas chromatography–mass spectrometry in vine leaves and in vine leaf infusions. It was observed that the volatile compounds present in vine leaves are dependent on the time of harvest, with benzaldehyde being the major volatile present in vine leaves collected at 30 days after harvesting. There are significant differences in the volatile composition of the leaves from the two grape cultivars, especially in the sample collected at 60 days after grape harvest. This is not reflected in the volatile composition of the vine leaf infusion made from this two cultivars, the more important being the harvesting date for the volatile profile of vine leaf infusion than the vine leaves grape cultivar.

Distributed monitoring system for precision enology of the Tawny Port wine aging process

Abstract Aging of Tawny Port wine is a multifactorial process critical for attaining the desired quality. Real time monitoring of important intrinsic and extrinsic factors that are known to affect the time and quality of the aging process are important to optimize and to manage the natural variability between wines aged in different long-used wood barrels. For this study, a distributed monitoring system was installed in sixteen oak barrels, placed in two adjacent wineries – one of them with controlled temperature – in the Douro Demarcated Region, Portugal. The monitoring process was performed using a RS-485 industrial network, which interconnects sensors that continuously measure wine temperature, pH, redox potential and wine’s dissolved oxygen, as well as other sensors that measure parameters related to the barrels’ environmental context, such as room temperature and relative humidity. This work presents the design, development and implementation of a remote distributed system to monitor such parameters, aiming to determine the existence of behaviour models for Port Tawny wine during aging in long-used oak barrels, depending on their storage history and to understand the evolution of wine pH, dissolved oxygen and redox potential in real winery conditions as well as their dependence on the wine’s storage temperature. This approach is based on easy-to-use embedded systems, with the aim of giving a relevant contribution to other projects in the area of precision enology.