Month: November 2018

Can panelists’ sensitivity be improved?

By Astrid Buica and Marianne McKay

Even though is difficult to reach consensus on the definition of a quality wine, there is agreement that a fault will easily result in a wine being rejected by experts and consumers alike. The presence of a fault can have immediate economic repercussions for the producers, from a single bottle being rejected based on “cork taint” to entire batches due to other types of faults such as “smoke taint”. In turn, this can also have farther reaching effects related to a brand’s image, such as loss of trust in a product.
Since wine aroma is considered as the proxy for wine quality, many studies focus not only on the positive but also on the negative impact certain compounds have. Pragmatically, an objective measurement of a compound by chemical analysis would easily solve the issue of the product not being released on the market if taint-causing compounds are present above their odour detection thresholds (ODTs). The issue comes in because ODT values are often reported in the literature in other matrices than wine (water or ethanoic solutions). Moreover, the ODT values are matrix-dependent. This means that even if a wine has been used for the determination of an ODT, another wine can produce different results due to the presence of other volatile and non-volatile compounds.
So practically, the acceptance or rejection of a wine is done by a panel of judges, used as “analytical panelists”. The question is, given that naturally the panelists can perceive a certain aroma, can they be fine-tuned for higher sensitivity through exposure? This is relevant, since, like any analytical tool, the panelists’ acuity should be tuned to the samples to be evaluated.

 

Alfredo Silva at Espaço Porto Cruz.

The results presented here are linked to an ODT confirmation study for five taint-causing compounds: guaiacol, o-cresol, 4-ethyl phenol (4EP), 3-isobutyl-2-methoxypyrazine (IBMP) and 2,4,6-trichloroanisole (TCA). The first three compounds are volatile phenols (VPs), associated to Brettanomyces contamination and smoke taint. IBMP is part of primary (grape-derived) aroma and is the main methoxypyrazine in many red and white cultivars. TCA is the key compound linked with cork taint. Aroma descriptors for these compounds cover a continuum from ‘burnt, smoky’ and ‘medicinal’ to the ‘mouldy, dusty’ flavours associated with cork taint, and ‘herbaceous, green’ aromas associated with methoxypyrazines. Since this work was part of a larger project, the medium for the testing was a partially de-aromatised unwooded Shiraz. The choice of cultivar was because Shiraz naturally doesn’t contain methoxypyrazines. There were 34 judges of varying abilities from novices to very experienced wine tasters. For the purposes of this study, we considered as ‘experienced’ judges (n=18) those who had been members of wine sensory panels the wine industry for at least six months and ‘inexperienced’ (n = 16) those who were not members of sensory panels and no formal wine sensory training. All judges indicated that they consumed wine on a regular basis. The experiment consisted of triangle tasting with control (unspiked) and spiked wines at ODT separately for each compound as the two types of samples presented to the judges.
Overall, the statistical results for inexperienced vs experienced judges indicated that the group effect was significant. In other words, experienced judges were better able to correctly identify samples spiked with the taint-causing compounds from control (unspiked samples). This could be due to a native sensitivity generally or through experience working on wine evaluation panels. Other researchers have already hinted at and recommended that adapted training for professionals in the wine industry will enhance abilities of judges to differentiate between spiked samples and controls, even at ODT levels.

On a per compounds basis, only trends could be observed (no statistical significance between means). For example, experienced judges seemed better able to detect the spiked samples in the case of guaiacol, o-cresol and IBMP. There was no difference at all between judges, whether experienced or inexperienced in detecting the spiked TCA samples, and little difference in the case of 4EP. This is interesting, since we expected that judges would be consistently sensitive to a class/type of compound, for example VPs, which turned out not to be the case. IBMP and TCA were the two compounds that showed the lowest number of correct judgments; it is possible that the judges experienced some sensory fatigue due to the order in which the samples were tasted. Ideally, each compound should be tested on different days, but logistical constraints forced us to have all tastings the same day.
In conclusion, even though the experiment was focused on ODT confirmation, the interesting aspect that emerged was the ability of judges to detect compounds more easily if they had some experience of winetasting. Training can possibly sensitize people to attributes that they might not have noticed previously. This is relevant in view of analytical tasters that can improve their performance by repeated exposure to compounds that are more difficult to detect. Another relevant aspect is the possibility of training industry members to sensitize them to off-flavours for early detection in the cellar rather than after a product is bottled and waiting to be released on the market.

Dr. Buica is a researcher in Oenology specialized in Analytical Chemistry applied to wine and related matrices, coordinator of Analytical activities and manager of the Analytical Laboratory in the Department of Viticulture and Oenology at the Stellenbosch University, South Africa. She graduated in 2000 as Chemist specialized in Analytical Chemistry at the University of Bucharest, Romania. She obtained her PhD in Analytical Chemistry at the Stellenbosch University, South Africa. Even though the topic of her PhD would have put her firmly in the field of nanotechnology applied to Separation Sciences, Dr Buica decided to follow another path when the opportunity arose in the Institute for Wine Biotechnology and the Department of Viticulture and Oenology at Stellenbosch. An Analytical Chemist at heart, Dr Buica dedicated most of her time to the Analytical activities and laboratory in the Department, developing methods for routine analysis of wine and related matrices. In the recent years, she has decided to slightly shift her focus to include Sensory Science in her work, to bring together these two fields relevant to Wine Sciences. Most of her projects have an important Sensory and Analytical component to them, in an effort to give a more comprehensive view to the evaluation of wine. As such, she delved into untargeted analyses (HR-MS, IR, NMR) and rapid sensory methods for rapid wine profiling, and into the fields of Chemometrics and Data Fusion.

 

Marianne got her BSc in chemistry and geography at the University of Cape Town (UCT), and went on to do an MSc (Agric) on aroma compounds in oak at Stellenbosch University (SU) under Professor Joel van Wyk, finishing in 1990. She was the first woman to graduate with an MSc (Agric) in SA. She then worked as a Scientific Officer in analytical chemistry at University of Cape Town for six years, running the ICP and HPLC services. She went to the United Kingdom (from mid-1997), and was involved in management of clinical trials for Helicobacter pylori, and then went on to run operations in validation services for pharmaceutical companies. Longing to return to academia, she accepted a post as lecturer in Oenology at Plumpton College near Brighton in 2000. On her return to South Africa in 2007, she accepted a post as lecturer in Oenology at SU. Her research portfolio includes interactions of volatile phenols in wine aroma, investigations in smoke taint, and she has an additional research focus in work-integrated learning and science curriculum transformation. She won the national South African Council for Higher Education Excellence in Teaching Award in 2015, and was awarded Distinguished Teacher status in 2017. She is currently a Teaching Fellow at Stellenbosch University.
Tel. +27 (0) 784 636 132; E-mail: marianne@sun.ac.za

 

Posted by in Enology

Autochthonous yeasts as a driver of innovation in the sparkling wine sector

By Vittorio Capozzi

The study and the employment of selected autochthonous yeasts in order to start and steer alcoholic fermentation in regional wines is a practice explored due to the aptitude of these biotypes to modulate wine quality. In fact, selected eukaryotic resources might offer solutions i) for the adaptation to specific environmental conditions, ii) for specific technical issues of oenological interest and/or iii) for differentiating organoleptic properties of final products (Martínez-Rodríguez et al., 2001; Torresi et al., 2011; Capozzi et al., 2015; Tofalo et al., 2016). This microbial regimen has been receiving increasing attention in reason of the recent evidences underlining an association of microbial diversity with vineyard environments (Bokulich et al., 2014; Knight et al., 2015), suggesting the existence of a sort of ‘microbial terroir’ to be exploited in oenology (Gilbert et al., 2014).
Sparkling wines contain high amount of CO2 and are the result of re-fermentation of a still wine, usually called base wine. Several ingredients, such as sucrose, selected yeasts, bentonite and some nutrients, are added to base wine in order to induce the re-fermentation. Then wines can be bottled, fermented and aged for a long period (about 9-12 months). The use of autochthonous yeasts as starter cultures for secondary fermentation has been recently suggested to enhance the specific features of typical regional sparkling wines and prevent fermentative problems (Torresi et al., 2011; Garofalo et al., 2016). Starter cultures selected for sparkling wine production must satisfy several characteristics, such as tolerance to high amount of ethanol, low pH, increasing carbon dioxide pressure, autolysis and flocculation.

Following the work by Vigentini et al. (2017), in a recent scientific article (Garofalo et al., 2018), we investigated the use of select autochthonous yeast resources for sparkling wine production. We genetically characterized about 160 Saccharomyces cerevisiae autochthonous strains isolated from “Uva di Troia” (an autochthonous Apulian (Southern Italy) grape variety used to produce “Nero di Troia” wine) spontaneous fermentation, after the evaluation of intraspecific diversity using interdelta analysis, we selected one representative strain for each of the 16 genetic cluster (Figure 1).

 

Figure 1.A graphical representation of the experimental plan followed in the study.

These strains were technological characterized at the lab scale and, successively, tested in winery for both induce alcoholic fermentation in base wine and re-fermentation of sparkling wine (Figures 1 and 2). For re-fermentation trials, yeast fermentative performances were tested in white and rosé sparkling wines obtained from Apulian grape varieties. We reported a complete polyphasic characterization of native yeasts for sparkling wine, highlighting a certain correlation between stress tolerance assays and fermentative aptitude and different performances of the same biotypes in base wine, white and rosé sparkling wines. The study, that for the first time includes VOCs determination in the characterization of autochthonous yeasts strains for during the re-fermentation phase, led to the selection of candidate starter cultures for Apulian sparkling wines.

The research was supported by the Apulian Region Project “Innovazioni di processo e di prodotto nel comparto dei vini spumanti da vitigni autoctoni pugliesi” (IProViSP) and carried out in collaboration with Carmela Garofalo, Carmen Berbegal, Francesco Grieco, Maria Tufariello, Giuseppe Spano, and people from the winery ‘Agricole Alberto Longo’.

Figure 2. The fermentation trials in bottles provided of aphrometer.

Vittorio Capozzi is researcher in Food and Agricultural Microbiology at the University of Foggia. His main research interest deals with the study of the complex impact of microorganisms on wine quality and with the understanding of the stressful life of malolactic bacteria in wine environment. Other ongoing research activities focus on the potential application of lactic acid bacteria and yeasts for the design of functional food, antimicrobial activity, flavour enhancements and nutritional improvements. He co-authored more than 100 scientific publications. ORCID: http://orcid.org/0000-0002-0717-0753; Scholar profile: https://scholar.google.it/citations?user=MC3xZQIAAAAJ&hl=it&oi=ao.

References:

Bokulich, N. A., Thorngate, J. H., Richardson, P. M. & Mills, D. A. (2014). Proceedings of the National Academy of Sciences (PNAS), 111, E139–E148
Capozzi, V., Garofalo, C., Chiriatti, M. A., Grieco, F. & Spano, G. (2015). Microbiological Research, 181, 75–83
Garofalo, C., Berbegal, C., Grieco, F., Tufariello, M., Spano, G., & Capozzi, V. (2018). International Journal of Food Microbiology, 285, 7–17
Garofalo, C., Arena, M.P., Laddomada, B., Cappello, M.S., Bleve, G., Grieco, F., Beneduce, L., Berbegal, C., Spano, G., & Capozzi, V. (2016). Fermentation, 2, 21
Gilbert, J. A., Lelie, D. van der & Zarraonaindia, I. (2014). Proceedings of the National Academy of Sciences (PNAS), 111, 5–6
Knight, S., Klaere, S., Fedrizzi, B. & Goddard, M. R. (2015). Scientific Reports, 5, 14233
Martı́nez-Rodrı́guez, A., Carrascosa, A. V., Barcenilla, J. M., Angeles Pozo-Bayón, M. & Carmen Polo, M. (2001). Food Microbiology, 18, 183–191
Tofalo, R., Perpetuini, G., Di Gianvito, P., Arfelli, G., Schirone, M., Corsetti, A., & Suzzi, G. (2016). Journal of Applied Microbiology, 120, 1574–1584
Torresi, S., Frangipane, M. T. & Anelli, G. (2011). Food Chemistry, 129, 1232–1241
Vigentini, I., Barrera Cardenas, S., Valdetara, F., Faccincani, M., Panont, C.A., Picozzi, C., & Foschino, R. (2017). Frontiers in Microbiology, 8, 1225

Posted by in Enology

wine summit: An open letter to Paddy Cosgrave

By Paula Silva

My name is Paula Silva and I am the responsible of Science & Wine blog, I want to thank you for following the blog and subscribe its philosophy. Last week, in the end of Web Summit 2018, you said that it is your intent to promote a Wine Summit, being Douro Region (Portugal) one of the possible locations to do it. You cannot imagine the happiness that I felt to hear you! In past years I was feeling like Don Quixote trying to create opportunities to researchers share their ideas, scientific concepts and discovers regarding wine. Encouraged by your declarations, I decided that the post of this week must be about science communication, which is very important to wine science. Therefore, in the following paragraphs I will try to summarize Science & Wine project and its contribution to science communication.
At 10 of September of 2017 occurred in Porto (Portugal) the “Science & Wine: From the terroir to the glass” conference. As the name indicates, it was a 1-day conference dedicated to a multidisciplinary discussion regarding wine. In the event were present more than 150 attendees from different groups including politicians, scientists, oenologists, agronomic engineers, students, managers among others.

 

Figure 1.Science & Wine: From the terroir to the glass. Porto, 10 September 2017. @Anabela Trindade

Inspired by this meeting Science & Wine blog was born in 22 of January of 2018, and publish articles about any issue related with wine, with a weekly periodicidy (Sundays). Until now, 48 posts were published with the contribution of several generous researchers with high scientific curriculums. Several topics were already approached including: the impact of climate warming in viticulture, wine and human health, precision viticulture, wine metabolome, wine microbiology, wine tasting, terroir, and wine technology. Science & Wine aims to make wine scientific data more accessible, therefore is a blog open to non-specialists and to anyone interested in the various aspects of wine science, even if it is someone not belonging to any scientific community. Creation of Science & Wine blog challenge me to venturing out of the science communication comfort zone into uncertain territory: the field where knowledge is applied.

Figure 2.Science & Wine blog posts

The success of both conference and blog, and the support of our followers, made me to believe that it is possible to do more and better. Then the 1st Science & Wine World Congress is being organized, which will take place 8-10 May 2019 in Alfândega Congress Centre in Porto. This event aims to bring together the experience of experts from industry, academia, research institutions, service providers, regulatory agencies and policy makers and design the wine that will be consumed in the future. To do this, it is important to understand how new technological advances could be used towards to wine production increase and wine quality improvement. Wine authenticity, wine health effects and sustainable practices of wine production are issues considered by consumers in their purchasing processes, therefore it is also important to discuss them when designing the wine of the future. This kind of conferences are good opportunities to scientists transform their energy and enthusiasm for passing on scientific information to the public.
In January of 2019 will begin Wine Science Cafés that will happen in the last Thursday of each month. They will star in Portologia in Porto under the subject “The chemistry of Port Wine”. In February our host will be “Casa de Pasto Chaxoila” in Vila Real, then Wine Science Cafés will travel from Portugal to the world. These events will start with a short talk, approximately 30 minutes, by an “expert” and after a break will come an hour or so of discussion, questions, comments, thoughts and opinions among speaker(s) and audience. This will be a great opportunity to engage in a two-way communication, where scientists can share new evidences, techniques, and applications but also will be aware of public expectations and concerns. This way, the scientific community could take up a more responsible role contributing to the success of future society, and along the way scientists and the rest of society can learn from each other. Wine Science Cafés will democratize science, meaning that science can also be participating and open in addition to being rigorous.

Figure 2.Wine Science Cafés

As a scientist and regarding science communication, I think that the relevant question is no longer if scientists should communicate but rather how to do so effectively both with each other and with public. Science communication initiatives differ widely in terms of target audience, mode of delivery, and overall aims and ideas. Scientists can go beyond face-to-face communication, through sharing resources and online approaches and, ultimately, forming networks of science communication where resources and knowledge can be distributed. In wine sciences, is crucial to improve the standing of fundamental research in society, and this is where we as individuals, but also media, societies or other organisations, can play a key part in helping to communicate and develop this important field. I hope that Science & Wine projects provide a motivation for this development, and that people feel encouraged to communicate their science effectively and inspired to collaborate with others to develop interdisciplinary partnerships that address both scientific and societal requests effectively.
So dear Paddy Cosgrave, welcome to the challenge of wine science communication. After your declaration I believe that scientists, politicians, industry and trade people, oenologists, viticulture and oenology experts, economists and many, many others are now more excited regarding wine issues. I hope that from now on Science & Wine could be recognized as a pioneer project and can count with more followers and with more support. So, I finish this letter as I began it, thank you Paddy Cosgrave.

 

Posted by in Curiosities

Scientific impressions about the influence of alternative winemaking on wine chemical and sensory features

By Maurício Castilhos

Brazil is a country with a discrete wine production when compared to the great world wine producers such as France, Italy and Spain. Wine production in Brazil is characterized by the relevant production of non Vitis vinifera  and wines. These grapes are not well known worldwide, since they are not commonly used for wine production. With a fruity flavor and aroma, these grapes are very appreciated by the Brazilian consumers. There is a classical region that produces wines from non Vitis vinifera grapes and responds for more than 80% of the wines produced in Brazil.  

With the aim of improving the quality of the Brazilian wines, some winemakers have employed different winemaking procedures to enhance wine color, to promote beneficial changes on wine aroma, and to enhance wine flavor, which result in wines highly appreciated by the consumers. Among the known winemaking procedures used in wineries, the grape pre-drying and the submerged cap attracted the attention of some researchers and winemakers since both procedures presented great chemical and sensory results.

In Brazil chaptalization procedure is allowed and consist in adding sucrose into the must to correct the alcoholic content of the resulted wine. This practice is allowed because Vitis labrusca Brazilian grapes do not reach enough sugar content, which is mandatory for producing wine with alcohol content between 8.6 and 14.0 % v/v. The grape pre-drying (Figure 1) consists in dry the grapes before the alcoholic fermentation aiming to increase grape soluble solid content. Grape pre-drying emerged as an alternative winemaking procedure to chaptalization one, since there are some studies reporting negative effects of chaptalization on wine features. Grape pre-drying procedure is based on the water evaporation aiming to concentrate the natural sugar present in grapes.

 

Figure 1. Grape pre-drying winemaking procedure. Source: De Castilhos & Del Bianchi (2016).

Some studies reported that the use of heat, even at low temperatures (about 60 ºC), degrade some phenolic compounds, such as anthocyanins, flavonols and hydroxycinnamic acid derivatives decreasing the antioxidant capacity of red wines. In contrast, the pre-dried wines presented higher flavan-3-ols concentrations when compared to wines elaborated with traditional winemaking procedures, originating wines with higher bitterness and astringency. Grape pre-drying results in important changes in red wines, promoting a jam note aroma, probably due to the significant presence of 2-phenylethyl acetate, which is considered as a positive change in Brazilian red wines, since it is well-accepted feature for consumers. Another positive result of the use of grape pre-drying is wine body enhancement, caused by water evaporation that concentrates grapes compounds.


Another winemaking procedure in Brazilian wineries, that can be considered as an alternative to the traditional winemaking one, is the submerged cap (Figure 2). This procedure promotes a constant contact between the solid parts (grape pomace) and the liquid part (grape must). The aim of this procedure is to enhance the release of grapes chemical compounds to must, improving chemical composition and causing a positive response on sensory features. Some studies also reported that the use of the submerged cap procedure enhance the yield of the winemaking reaching about 65 % of the total yield.

Figure 1. Grape submerged cap winemaking procedure. Source: De Castilhos & Del Bianchi (2016).

The submerged cap winemaking also provides some relevant results regarding the concentration of phenolic compounds, showing a discrete increase on the phenolic concentration. This result is probably linked with the constant contact between the must and pomace, enhancing the extraction of the phenolic compounds existent in the solid parts. The improvement of the phenolic concentration provides an intense color for the wine and some punctual changes regarding aroma and flavor. In a recent study, the submerged cap winemaking procedure provided a vegetal note on wines due to the higher concentration of C6 alcohols. In the same study, which provided information about the aroma of two non Vitis vinifera wines, the authors reiterated the fruity flavor of the wines mainly due to the presence of higher concentrations of ethyl and methyl esters and acetates.

Alternative winemaking procedures are suitable for wines, because these beverages presented high chemical and sensory complexity, which influence the high or low consumers acceptance. Since every sensory change has a chemical one that explains it, all the chemical changes observed due to the application of variations in winemaking will result in sensory changes, and these changes can be considered good or bad for the wine. In this context, the study of these alternative procedures is crucial for the improvement and evolution of the winemaking and wineries, producing wines with different chemical profiles and, consequently, different sensory features, which can be responsible for their higher acceptance.

Maurício Castilhos is graduated in Food Engineering, Master and PhD degree in Food Science and Engineering from São Paulo State University (Unesp), Institute of Biosciences, Humanities and Exact Sciences, São José do Rio Preto, SP, Brazil. Castilhos is Food Technology professor and researcher at Minas Gerais State University (Uemg), associate editor from Food Research International Journal, and have experience in alternative winemaking technologies and their influence on wine chemical and sensory properties. In addition, Castilhos have experience in phenolic and volatile composition using instrumental chemistry applying High Performance Liquid Chromatography Gas Chromatography, both coupled with Mass Spectrometry (HPLC-MSn / GC-MS), respectively. Recently has developed researchers concerning the wine metabolomics in order to fulfill the gap existent in Brazil regarding Geographical Indication of Provenance using HPLC-QTOF-MS-MS and Nuclear Magnetic Ressonance (NMR) analytical techniques. Castilhos also has experience in wine sensory analysis and statistical approaches, using them in order to improve the descriptive and acceptance wine sensory studies.

References:

De Castilhos, M. B. M. & Del Bianchi, V. L. Winemaking procedures and their influence on wine stabilization: effect on the chemical profile. In Jordão, A. M. & Cosme, F. (editors), Recent Advances in Wine Stabilization and Conservation Technologies, Nova Science Publishers Inc., 2016.

Posted by in Enology