Oak volatiles

The use of oak for the ageing of premium wine products is commonplace in the wine industry. It is primarily used to increase complexity and to add oak flavours to wines. There is now a method for analysing the effect of oak storage on wine flavours and, from this, an opportunity for winemakers to gather information that will allow them to determine optimal barrel storage.

Volatile compounds derived from oakwood are important contributors to wine aroma and flavour. Such compounds include:

cis- (and trans-) oak lactone

Cis- (and trans-) oak lactone–apparently the most important oak-derived flavour compound in wine-is responsible for a variety of sensory characteristics and is chiefly responsible for the greater intensity of vanilla and coconut-like aromas found in wines matured in different types of oak. These lactones are present in the raw material and vary substantially from one sample to another. The amounts present in oak can be affected by seasoning but not in a predictable way. The presence of these compounds in oak is not greatly affected by coopering variation but, in some samples, increasing toasting levels can slow down the rate of lactone extraction and reduce their impact on wine flavour.

Guaiacol and 4-methylguaiacol

Guaiacol and 4-methylguaiacol have smoky aromas and are indicators of the relative toast levels of barrels. These compounds are formed almost exclusively by the degradation of lignin during the toasting process. The degree of toasting is, therefore, an important factor in imparting a smoky character in wines. The use of wood smoke is another source of these compounds and the burning of oak offcuts during the coopering process may also enhance this character.

Vanillin

Vanillin is the main flavour compound in natural vanilla. It can be extracted in significant quantity from unheated oak wood and in even higher amounts from strongly heated wood. It is generally considered to be an important contributor to the character of barrel-aged wines. Vanillin can be transformed by yeast metabolism during fermentation and vanillin concentration can be reduced considerably if primary fermentation is carried out in the barrel. In general, vanillin is formed in increasing amounts with increased toasting levels and is not influenced by origin or seasoning period. Analysis of this compound can be used to determine future toasting levels that are appropriate for the chosen wine variety and style.

Furfural and 5-methylfurfural

Furfural and 5-methylfurfural are generated by the breakdown of carbohydrates, in particular cellulose and hemicellulose, during the toasting process. These compounds have a sweet, caramel or butterscotch aroma and are often present at levels greater than 1000 µg/L in wine. The concentration of these compounds can decrease during heavy toasting levels.

 


Prices per analysis (excluding GST)
Analysis 1-7 samples 8+ samples
Oak volatiles including 4-EP and 4-EG in wine $112 $98
Oak volatiles in oak $124 $110
Target response time – 10 working days
Volume required
  • Wine: 20 mL
  • Wood: 50 g

How does the analysis work?

A new analytical method employing gas chromatography/ mass spectrometry and using deuterium-labelled standards has been developed for accurately determining the concentration of all of these compounds in wine or in oak shavings in a single analysis. Oak shavings and chips are first steeped in a model wine for seven days and the model wine extract is analysed as for wine samples.

How can this analysis assist winemakers?

The analytical data will enable the industry winemakers, cooperages and barrel suppliers to assess the total flavour potential of oak wood and to evaluate the relative merits of various types of oak treatment in wine production. Results of this anlaysis will enable the winemaker to determine whether the raw material (oak lactone concentration), the toasting level (guaiacol and 4-methylguaiacol), or Brettanomyces activity (4-ethylphenol) has contributed to the flavour differences in the wine. Results may also serve as an objective indicator for the purchase of new barrels or for the re-shaving and toasting of old barrels. Furthermore, analysis of wines during barrel storage may provide information that will enable winemakers to optimise the desired oak derived flavours by manipulating the time spent in barrels of different types.

Wineries and suppliers can also determine the flavour potential of oak by analysing subsamples of oak lots prior to coopering, or can assess the flavour potential of oak chips prior to addition. Suppliers can also use results as a quality control tool for manufacturing processes.

Analysis of oak chips prior to addition can also be undertaken in conjunction with an analysis for trichloroanisole (TCA) to ensure that the wine does not become accidentally tainted by such an addition.

Note. This analysis is not suitable for assessing the flavour potential of finished barrels prior to use.

For more information please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au.