Wine ageing: Managing wood contact time.

Abstract

Barrel ageing is a transformative process that alters a wine’s organoleptic properties and consequently its price. Even though it is considered beneficial mostly for red wines, ageing can also be used for white wines but for shorter time periods. Due to barrel costs, space requirements and the markets’ demands for fast release of each new vintage, new products such as oak chips or shavings have been developed to help minimize the time needed for the extraction of essential wood compounds. Regardless of the shape or type of the wood used for ageing, managing time of contact is a challenging task, based mostly on wine tastings by professionals, as chemical analyses related to ageing are laborious, costly, require highly educated personnel and cannot be performed in the winery. For this reason, the development of a tool for the management of the optimum time of contact is of grave interest for winemakers and enologists. In this experiment, extraction from chips with various toasting degrees was monitored with the use of Fourier Transform Infrared Spectroscopy (FT-IR) for a period of eight weeks. FT-IR was selected due to its cost-effective nature and speed, and its successful application in wine authentication. The wine used, was a monovarietal white wine from the Greek market, while the chips were from Tonnellerie Nadalié and included untoasted, Noisette, medium and heavy toasting degrees. The chips were added to 200 ml of wine (2 repetitions per sample) at a ratio of 3 g/L and samples were filtered and measured every two weeks. Measurements were performed in triplicate on a IROS 05 spectrometer from Ostec Instruments in ATR mode at the spectral range from 4000 to 400 cm-1. JMP v.16 software (SAS Institute Inc, 2022) was used for statistical analysis.The spectral profile obtained for each sample revealed clear differences in the range from 2000 to 900cm-1. Less peaks were observed in samples from wines with untoasted chips, while the highest peaks were observed in samples from chips with Noisette toasting. Moreover, based on the range from 2000 to 900cm-1Principal Component Analysis produced a clear differentiation in wines from the second sampling (4 weeks’ time of contact), when according to most manufacturers’ guidelines the highest extraction of wood compounds is observed. The first two Principal Components explain 87,8% of the variance. A sub-grouping based on the type of toasting was also evident, however only in the group of the second sampling. Performing PCA on each sampling revealed clear groupings based on toasting as well, with the first two PCs explaining close to 90% for all four analyses. These preliminary results show good potential for the development of a tool based on which samples that have reached maximum extraction can be differentiated.