Toasting level analysis - Botti Gamba Level...Test method ISO 4121: 2003. Tasters number 14 tasters...

FABBRICA BOTTI GAMBA S.r.l.

Toasting level analysis

Caudana Alberto DISAFA 2019


Material and methods One lot of oak has been divided in 9 parts to build 9 barrels. From every barrel a sample was taken before toasting. Then the barrels have been divided in group of three and toasted at light, medium and heavy toasting level.

From the inner surface of the barrel, once toasted, samples have been taken (1-3 mm of material).

All the samples have been then put in contact with a white wine (Alcohol: 11,73 % - pH: 3.29 – Total acidity: 5.51 g/l), in the quantity of 80 g/L for a month at room temperature.

At the end the parameters were determined to characterize the tannin content by adopting OIV techniques for wines and aromatic molecules by GC-mass with the following characteristics: Injector Splittles, Capillary Column DB-WAX (length 30m; internal diameter

0.25mm and 0.25m film thickness. 5975C quadrupole mass detector. MSD Chemstation G1701EA E.02.00.493.

In addition to the gas chromatographic analysis we tried to characterize the

different toasting levels by a sensory analysis. For this test 10 g / l of wood removed from the inside of the barrels were macerated 20 days at room temperature in white wine with the following characteristics: Alcohol 12.7% vol, Total acidity 5.15 g / l Total extract 18.9, pH 3.2, Volatile acidity 0.26 Total sulfur dioxide 93 mg / L. The panel was asked to characterize the wine by focusing on some descriptors reported in the bibliography, omitting those already highlighted through the gas chromatographic analysis.

Sensory analysis - Test conditions - Tasting table: clean and without extraneous odors - ISO tasting glasses: clean, with no haloes, patches and / or foreign odors - Temperature of the tasting room: 21.3 ° C - Hygrometric status of the tasting room: 61% - Sample temperature: 18.3 ° C Purpose of the test

After examining the samples, assign an intensity value from 0 to 10 to each of the proposed descriptors: Chocolate, Toast, Licorice, Pepper, Tobacco, Cotton Candy, Caramel

The tasters were asked to describe the samples using a discrete, numerical and

unipolar scale.


Average

Average

Average

Average

Dev St

Dev St

Dev St

Dev St

U.M.

Untoasted oak Heavy

Medium

Light Untoasted oak

Heavy

Medium

Light

DO 280 nm ABS X 100 82 36 49 55 7 1,1

15 5 Total dry extract g/l 14 12 13 13 0 0,

1 0,2 0,2

Total polyphenols mg/l 1832 602 969 1065 555 39

377 172 Total tannins mg/l 115 44 72 66 12 2 12 6 Condensed tannins % 3,5 3,4 3,2 2,1 1,5 1,

5 2,6 3,0

The samples, anonymized, were presented to the taster consecutively and analyzed individually Test method ISO 4121: 2003. Tasters number 14 tasters meeting the ISO 6658: 2005 standard * The tasters were selected and trained as indicated in the ISO 8586 standards:2012.

Results The hydrolysable tannins in the wood are mainly two ellagitannins: vescalagina and castalagina. These molecules are water-soluble and rapidly pass in hydro-alcoholic solution such as wine and spirits. Their oxidability and their sensory properties play an important role in the course of refining the wine in oak barrels. The results confirm that the toasting level has a significant influence both on the total tannin concentration and on the condensed fraction. (table 1 and figure 1).

Tab 1. Main parameters analyzed before and after toasting


The total polyphenol content and optical density (DO 280) also show a similar trend. The data clearly indicate that the higher the toasting level, the lower the total concentration of tannins that can be transferred to the wood, which translates into a lower or greater impact on the astringency of the wine.

Several works have confirmed that the ellagitannins from the heartwood of the oak are degraded or transformed by high temperatures, thus reducing their extractability.


The behavior of the total dry extract is different, as it is not affected by the degree of toasting (fig.3).


The intensity of toasting determines profound physical changes in the wood in particular: - light toasting level modifies lignin and hemicelluloses while cellulose is not modified. - at a medium toasting level the constituents on the surface disappear by fusion. - at a heavy toasting level the cellular structure is strongly disorganized. These physical transformations are accompanied by a chemical evolution produced by the modifications of the parietal polymers (cellulose, hemicellulose and lignin) which have different melting points and originate a great variety of products. The benzoic aldehydes such as vanillin originate from the degradation of lignin. This increases when increasing toasting till a certain point and then starts decreasing. For pyrolytic demolition of lignin, volatile phenols originate such as guaiacol, 4-methyl guaiacol, 4 vinyl guaiacol, eugenol, which give the wine a hint of smoked - spicy. From the thermal degradation of the polysaccharides of the wood such as cellulose and hemicellulose derive the furan aldehydes that give odors of almond (furfural) and toasted almond (5 methyl furfural). Finally, the heating of the wood causes the thermal degradation of lipids with the formation of isomers of the methyloctalactone.

Among the most important is the methyl gamma octa-lactone commonly called whiskeylactone. The cis isomer is the most odorous and is predominant in wood. After toasting it is found in even greater concentrations until it disappears with heavy toast. The whiskeylactone gives a smell of coconut, fresh wood.

The aromatic compounds detected during the test are shown in figure 4. The histograms follow the average of the result of the three samples while the bar indicates the standard deviation between the replicas.


16000

14000

µg/kg

Heavy Medium Light

12000

10000

8000

6000

4000

2000

0

Guaicolo Whyskey lattone Eugenolo 4-Metilguaiacolo

350000 µg/kg

Heavy Medium Light

300000

250000

200000

150000

100000

50000

0

5-Metilfurfurale Furfurale Vanillina Siringolo


The effects of the different toasting level are pretty evident.

Starting with light toast the smell of toasted almonds (5 methyl furfural) and cloves

(eugenol) are more evident.

Keeping on toasting and reaching the medium toasting level, we can note how

vanilla (vanillin), and coconut / oak (whiskey lactone) prevail. The contribution of the

4-methyl guaiacole is also important highlighting the spicy character.

Reaching heavy toast we can point out how hints of smoked (guaiacol), toasted (4-

methylguaiacol), ash (siringol) and almond (furfural) prevail.

The results are in line with what emerges from the bibliography in relation to the

effect of the intensity of roasting on the wood.

In figures 5-6-7 the volatile compounds have been represented in a spider graphs to

more effectively represent the aromatic profile of the different toasting levels.

For graphic reasons, some compounds have been multiplied by a factor of 10 or 100

as shown in the legend.


Figure 5. Representation of the concentration of volatile compounds in light toast


Figure 6. Representation of the concentration of volatile compounds in medium toast


Figure 7. Representation of the concentration of volatile compounds in heavy toast

Results of sensory analysis For each wine the score attributed to each descriptor by the different tasters was added and reported as a percentage of the total sum. The results denote three different sensory profiles: In heavy toast, tobacco and pepper prevail, while in medium toast, we can point out the sweet character of the toasting with cotton candy and chocolate prevailing over other sensations. In light toasting licorice and toasted bread have been noted (fig. 8, 9 and 10). The results of the sensory analysis highlight other distinctive features produced by the different degrees of toasting that complete the profiles outlined with the GC-MS analysis.


Figure 8. Sensory profile as a percentage of the total descriptors of light toast


Figure 9. Sensory profile as a percentage of the total descriptors of medium toast


Figure 10. Sensory profile as a percentage of the total descriptors of heavy toast


FINAL CONSIDERATIONS

Putting together the results coming from gas chromatographic analysis and the sensory analysis, together with the tannin extraction we can point out the following characteristics for each toasting level, showing very different profiles:

Untoasted oak (for big cask only): higher presence of tannins, that have been not reduced by toasting. The bigger volume of the cask helps giving an elegant character and softening the impact of the untoasted oak, while highly lifting the fruit character of the wine, without any impact of toasty nuances.

Light toast (190 °C for 40 minutes): the smell of almonds and clove are evident. Hints of licorice and toasted bread can be noted as well. The toasty nuances leave a lot of room to the fruity characteristics of the wine. Tannins are more present here compared to other toasting levels.

Medium toast (205 °C for 45 minutes): we can note how vanilla, and coconut / oak (from the whiskey lactone) prevail. The impact of cotton candy, chocolate and butterscotch are also important highlighting the sweet character of this toast level. The contribution of the 4-methyl guaiacol is also important giving a bit of a spicy character. The tannins are more degraded, giving less astringency, with a good balance between the fruitiness of the wine and the toasty nuances described above.

Heavy toast (220 °C for 53 minutes): At this toasting level the sweet notes tend to decrease leaving room to the smoked, toasted nuances. At the sensory evaluation also tobacco and pepper have a good impact. The tannins are much less present at this point compared to the other toasting levels.

In the wine we should note a much higher tone of the toasty and smoke character over the fruitiness of the wine.

Toasting level analysis - Botti Gamba Level...Test method ISO 4121: 2003. Tasters number 14 tasters...

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