EN
English
French
- Chris Boiling
- 2024-04-24
In the usual red winemaking process, grapes are destemmed between the harvest and the filling of the tank. However, in regions like Bourgogne and Beaujolais, some winemakers leave all or a percentage of stems in contact with the juice during the early stages of fermentation. This choice is significant and is likely to affect the sensory properties of the resulting wine.
Is that why winemakers add whole bunches or stems to fermentations?
The addition of whole clusters can impart unique flavours and aromas to the wine, increase tannin levels, enhance mouthfeel, and help balance the fruit flavours with additional structure and complexity.
Why doesn’t every winemaker do it then?
It only seems to work effectively with certain grape varieties, when the stems are mature, and for certain wine styles.
For example, studies have revealed the presence of volatile compounds with a green aroma, namely methoxypyrazines or methyl salicylate, in Cabernet Sauvignon wines made from whole bunches compared with wines made from destemmed bunches. Stems also have a reputation for producing more astringent and slightly bitter flavours (which is probably linked to the higher concentration of proanthocyanidins).
What’s the best percentage of stems to include?
That very much depends on the winemaker, ripeness level, grape variety, maceration time, vineyard, and vintage. Canopy recently visited the spiritual home of carbonic maceration, Beaujolais. All the winemakers we visited and spoke with were making red wines from Gamay grapes. The quantity of stems added ranged from 100% to 20%, with 70%, 50%, and 30% quite common. Canopy also recently interviewed Lucas Löwi, estate director at Terrazas de los Andes in Mendoza, Argentina, who uses 20% whole bunches in the new flagship Terrazas de los Andes Extremo Malbec because he likes the soft, rounder tannins produced by semi-carbonic maceration. It’s the only wine in the Terrazas de los Andes portfolio with an element of semi-carbonic maceration because the wood lignifies superbly in the 1,650m-high El Espinillo vineyard. Lucas describes the stems as “more mature, more burnt”.
What do we know about stems?
A new study, which focused on the effect of stems on the concentration of a sweet compound called astilbin, investigated the effect of adding stems during the winemaking process.
But, firstly, the researchers wanted to discover its taste detection threshold. This was established at 5.7mg/L in a wine model solution. Commercial wines were then analysed, demonstrating that Pinot Noir and Gamay wines contained higher concentrations of astilbin than wines made from a blend of Merlot or Cabernet Sauvignon. Moreover, the concentrations of astilbin found in wines from Pinot Noir and Gamay were above the taste detection threshold, suggesting that astilbin contributed directly to their perceived sweet taste.
The second part of the study was based on some experiments carried out at several French wine estates, in Bourgogne, Beaujolais and Bordeaux, over three vintages to investigate the influence of whole-bunch vinification. The addition of stems during vatting significantly increased astilbin concentrations. In addition, the researchers discovered the increase in astilbin concentration varied according to grape variety. The ratio between the astilbin concentration of wines made from grapes with added stems and wines made exclusively from destemmed bunches was higher in Merlot than in Pinot Noir and Gamay. This is because astilbin is found in equal proportions in the stems and skins of Gamay and Pinot Noir.
What exactly did the study find?
Firstly, that people’s thresholds for astilbin ranged from 0.45 mg/L to 56.5 mg/L, but the average of 20 tasters (8 men and 12 women) was 5.7 mg/L. Analysis of 123 commercial red wines found astilbin at a mean concentration of 9.2 ± 2.2 mg/L – higher than the taste detection threshold for astilbin. “This means that astilbin can contribute to the taste balance of various wines,” said the researchers, Marie Le Scanff and Axel Marchal.
They also found a difference between grape varieties, with blends dominated by Cabernet Sauvignon or Merlot having an average concentration of astilbin of 2.2 ± 0.2 mg/L. This concentration was around ten times lower than those found in wines made from Gamay or Pinot Noir, which amounted to 19.9 ± 3.1 mg/L and 24.6 ± 4.2 mg/L, respectively. “In addition, statistical tests showed that this difference was significant at the 0.1% level,” said the researchers.
The average concentration of astilbin found in wines made from Gamay and Pinot Noir was above its detection threshold. This suggests that astilbin had a stronger effect on sweetness in these wines than in wines made from Cabernet Sauvignon or Merlot. Some of the Pinot Noir and Gamay wines came from the Beaujolais and Bourgogne regions, where whole-bunch vinification – which can increase the release of astilbin – is practised. So, the effect of the addition of stems during vinification was also studied.
The experiments carried out in Bordeaux estates on vinified Merlot wines showed an increase in astilbin until the eighth day, when alcoholic fermentation had finished, for the “30% whole bunches” modality with a concentration reaching 8.7 mg/L. In the “destemmed” vat, the maximum astilbin content was measured at 6 mg/L on the sixth day of vinification. The difference calculated between the two modalities was 31% of the maximum content. For the second experiment in Bordeaux, the astilbin concentration stabilised at around 5 mg/L for the “destemmed” modality and 8.4 mg/L for the “30% whole bunches” modality around the 11th day of vinification, that is seven days before the end of alcoholic fermentation. Here, the percentage difference was estimated at 40%.
With regards to the experiments carried out in Bourgogne with Pinot Noir, astilbin concentrations in the wines stabilised from the eighth day, at around 26 mg/L for the “destemmed” vat and around 32 mg/L for the vat with “50% whole bunches”. For the vat with “30% whole bunches”, astilbin levels reached 31 mg/L at the end of alcoholic fermentation but decreased to 24 mg/L five days later, which was slightly lower than the concentration measured in the “destemmed” vat at the same stage. However, the difference between the “destemmed” and “50% whole bunches” modalities was 19%. In the second experiment in Bourgogne, the concentration in the “destemmed” vat stabilised at around 30 mg/L two days before the end of alcoholic fermentation. For the “50% whole bunches” vat, the content increased to 38.8 mg/L in the sample taken five days after alcoholic fermentation. On the 14th day, the concentration of astilbin in the “destemmed” vat was 26% lower than in the vat with “50% whole bunches”.
The experiments on Gamay wines carried out in the Beaujolais region confirmed the previous observations. Astilbin levels increased between the eighth and 11th day of vinification, that is, before the end of alcoholic fermentation. Wines from Plot A vinified in 2020 and 2021 contained higher concentrations of astilbin than those from Plot B in the corresponding modality and vintage. The maximum concentrations found were 46 mg/L for the “30% whole bunches” modality, 42 mg/L for the “15% whole bunches” modality and 38 mg/L for the “destemmed” modality. These concentrations were slightly higher than those measured in the Pinot Noir and much higher than those in the Merlot wines. However, the differences between the “destemmed” and “30% whole bunches” modalities were 17% and 6%, respectively, for Plots A and B in the 2021 vintage.
In general, these experiments demonstrated that the addition of stems during winemaking increased the content of astilbin in the wines, regardless of the grape variety. Furthermore, the difference in astilbin content between modalities with and without the addition of stems varied according to the grape variety. Moreover, the majority of the extraction of astilbin occurred during the first part of alcoholic fermentation. This compound was, therefore, released into the aqueous phase when the juice still had low alcohol levels. This is also the case for flavonols such as quercetin and kaempferol, whose levels increase gradually between the fifth and seventh day of fermentation. In addition, astilbin concentration in modalities without stems seems to reach its maximum faster than in modalities with stems. This could suggest that astilbin present in the skins was released before that present in the stems.
How does astilbin content vary in grape varieties?
To study the influence of the grape variety, the total concentrations of astilbin in the bunches were calculated. Bunches of Pinot Noir contained an average of 17.5 ± 7.2 µg/g fresh extract, significantly more than Merlot bunches, with 8.6 ± 2.3 µg/g fresh extract. The average content in Gamay bunches was between the two grape varieties, at 10.3 ± 1.9 µg/g fresh extract.
From a global perspective, the stems were, therefore, the component containing the most astilbin, around five times more than the skins in our study. Nevertheless, on the scale of a bunch, the constituents were found in different proportions. After the separation of each cluster, the mass of each component was measured and the average proportions of each component in relation to the overall mass of the bunch were calculated for each grape variety. Pulp was the main component of the bunch, accounting on average for 79.4% for Gamay, 71.6% for Pinot Noir and 78.8% for Merlot. It is followed by skins (12% for Gamay, 16.3% for Pinot Noir and 12.7% for Merlot), seeds (5.2% for Gamay, 6.9% for Pinot Noir and 5.5% for Merlot) and, finally, stems (3.4% for Gamay, 5.1% for Pinot Noir and 3.1% for Merlot).
The differential effect of the grape variety on the astilbin concentration was measured with and without stem addition. Astilbin concentrations were higher in Gamay and Pinot Noir wines than in Merlot wines. For Gamay, the average concentrations were 27.7 and 31.9 mg/L for the “destemmed” and “with stems” modalities, respectively, and for Pinot Noir, the concentrations were 23.9 and 30.3 mg/L for these two modalities. For wines with a majority of Merlot, the average concentration was 5.6 mg/L for the “destemmed” modality and 8.8 mg/L for the “with stems” modality. In comparison with the taste detection threshold, the mean value of astilbin concentration with the addition of stems in Merlot wines exceeded this threshold, which was established at 5.7 mg/L. Finally, the addition of stems provided an average increase of 4.1 mg/L, 6.3 mg/L and 3.2 mg/L of astilbin for wine made from Gamay, Pinot Noir and Merlot, respectively.
Nevertheless, it is interesting to note that the difference in astilbin proportion between the two methods (“destemmed” and “with stems”) appeared to be greater for Merlot than for Gamay and Pinot Noir. In fact, the presence of stems during vinification contributed an average of 36% more astilbin for Merlot, compared with 21% for Pinot Noir and 12% for Gamay.
Does astilbin only come from stems?
No, the study also measured astilbin concentration in the various parts of the bunch, namely the stems, skins, seeds and pulp, and the differences between the grape varieties.
The results showed that the addition of stems during vatting significantly increased astilbin concentration. Furthermore, this increase varied according to the grape variety. Whereas the astilbin contents were lower in Merlot wines than in Pinot Noir or Gamay wines, the ratio between its concentration of wines from the two modalities was higher in Merlot than in Pinot Noir and Gamay.
The localisation of astilbin in the different components of the bunch, depending on the grape variety, was also investigated to understand this difference better. Thus, a higher abundance of astilbin in stems than in skins was found in the Merlot variety, whereas for Gamay and Pinot Noir, the total quantity of astilbin in a bunch was located in equal proportions in stems and skins.
This means that for a bunch of Gamay and Pinot Noir, the proportion of astilbin came half from the stem and half from the skins, whereas for Merlot, two-thirds of the total astilbin in a bunch was found in the stem.
How else do stems affect the composition of the wine?
The average pH was calculated at 3.46 ± 0.04 for the destemmed wines and 3.52 ± 0.04 for the ones with stems. Concerning the average alcohol content, it was calculated at 13.79 ± 0.82% for the destemmed modality and 13.68 ± 0.84% for the with-stems samples. The difference between these modalities was not significant.
Other studies have found the alcoholic degree lower in wines vinified with stems than in wines made from totally destemmed clusters. This difference is generally explained by the composition of the stem, which is rich in water and low in sugars. The water in the stems may dilute the must, while the ethanol formed during alcoholic fermentation is absorbed by the stems. In addition, some studies have described a decrease in acidity in wines made with stems due to the high potassium content of the stems, which can precipitate with tartaric acid. But, generally, these observations were made on wines for which all the stems were kept during vinification. The impact of a low proportion of stems (no more than 50% of whole bunches) on these parameters was measured in the new study, which discovered that adding between 15 and 50% of stems during vinification “did not seem to have any effect on pH or alcoholic strength”.
What’s the influence of the vintage?
The influence of vintage on astilbin contents in wines and stems from the same terroir was also studied. During the 2019, 2020 and 2021 vintages, samples of Pinot Noir stems were taken from nine different plots at an estate in Bourgogne. The average concentration for the 2020 vintage was measured at 2 ± 0.4 mg/g, almost double that of the 2021 vintage, measured at 1 ± 0.1 mg/g. For the 2019 vintage, the average concentration is 1.3 ± 0.3 mg/g.
In addition, astilbin levels were measured at the end of vinification in wines from the corresponding plots. The average astilbin concentrations of the 2019 and 2020 vintages, 43.8 ± 2 mg/L and 47.7 ± 3.9 mg/L, respectively, were significantly higher than those of the 2021 vintage (27.1 ± 1 mg/L). The 2021 vintage saw more rainfall and caused less water stress on the vines.
Click here to access the full study, ‘New insights about sensory contribution of grape stems during winemaking: role of astilbin, a sweet polyphenol’, which was published in OENO One, Vol. 58 No. 1 (2024).
Is that why winemakers add whole bunches or stems to fermentations?
The addition of whole clusters can impart unique flavours and aromas to the wine, increase tannin levels, enhance mouthfeel, and help balance the fruit flavours with additional structure and complexity.
Why doesn’t every winemaker do it then?
It only seems to work effectively with certain grape varieties, when the stems are mature, and for certain wine styles.
For example, studies have revealed the presence of volatile compounds with a green aroma, namely methoxypyrazines or methyl salicylate, in Cabernet Sauvignon wines made from whole bunches compared with wines made from destemmed bunches. Stems also have a reputation for producing more astringent and slightly bitter flavours (which is probably linked to the higher concentration of proanthocyanidins).
What’s the best percentage of stems to include?
That very much depends on the winemaker, ripeness level, grape variety, maceration time, vineyard, and vintage. Canopy recently visited the spiritual home of carbonic maceration, Beaujolais. All the winemakers we visited and spoke with were making red wines from Gamay grapes. The quantity of stems added ranged from 100% to 20%, with 70%, 50%, and 30% quite common. Canopy also recently interviewed Lucas Löwi, estate director at Terrazas de los Andes in Mendoza, Argentina, who uses 20% whole bunches in the new flagship Terrazas de los Andes Extremo Malbec because he likes the soft, rounder tannins produced by semi-carbonic maceration. It’s the only wine in the Terrazas de los Andes portfolio with an element of semi-carbonic maceration because the wood lignifies superbly in the 1,650m-high El Espinillo vineyard. Lucas describes the stems as “more mature, more burnt”.
What do we know about stems?
- At full ripeness, the stems represent between 3 and 7% of the weight of the fresh bunch.
- They are very rich in water (around 80% of their total composition) and low in sugar (less than 1% of their total composition).
- The proportion of phenolic compounds represents between 2 and 4% of the total composition of the stems. In addition, in a bunch, the stem can contain up to 20% of the total phenolic compounds despite its low proportion by mass.
- It also contains acids, nitrogen compounds, mineral compounds and ligneous matter.
- Phenolic compounds are found in their polymeric form. Proanthocyanidins have often been described in stems, with a higher mean degree of polymerisation and a higher percentage of prodelphinidins than in seeds.
A new study, which focused on the effect of stems on the concentration of a sweet compound called astilbin, investigated the effect of adding stems during the winemaking process.
But, firstly, the researchers wanted to discover its taste detection threshold. This was established at 5.7mg/L in a wine model solution. Commercial wines were then analysed, demonstrating that Pinot Noir and Gamay wines contained higher concentrations of astilbin than wines made from a blend of Merlot or Cabernet Sauvignon. Moreover, the concentrations of astilbin found in wines from Pinot Noir and Gamay were above the taste detection threshold, suggesting that astilbin contributed directly to their perceived sweet taste.
The second part of the study was based on some experiments carried out at several French wine estates, in Bourgogne, Beaujolais and Bordeaux, over three vintages to investigate the influence of whole-bunch vinification. The addition of stems during vatting significantly increased astilbin concentrations. In addition, the researchers discovered the increase in astilbin concentration varied according to grape variety. The ratio between the astilbin concentration of wines made from grapes with added stems and wines made exclusively from destemmed bunches was higher in Merlot than in Pinot Noir and Gamay. This is because astilbin is found in equal proportions in the stems and skins of Gamay and Pinot Noir.
What exactly did the study find?
Firstly, that people’s thresholds for astilbin ranged from 0.45 mg/L to 56.5 mg/L, but the average of 20 tasters (8 men and 12 women) was 5.7 mg/L. Analysis of 123 commercial red wines found astilbin at a mean concentration of 9.2 ± 2.2 mg/L – higher than the taste detection threshold for astilbin. “This means that astilbin can contribute to the taste balance of various wines,” said the researchers, Marie Le Scanff and Axel Marchal.
They also found a difference between grape varieties, with blends dominated by Cabernet Sauvignon or Merlot having an average concentration of astilbin of 2.2 ± 0.2 mg/L. This concentration was around ten times lower than those found in wines made from Gamay or Pinot Noir, which amounted to 19.9 ± 3.1 mg/L and 24.6 ± 4.2 mg/L, respectively. “In addition, statistical tests showed that this difference was significant at the 0.1% level,” said the researchers.
The average concentration of astilbin found in wines made from Gamay and Pinot Noir was above its detection threshold. This suggests that astilbin had a stronger effect on sweetness in these wines than in wines made from Cabernet Sauvignon or Merlot. Some of the Pinot Noir and Gamay wines came from the Beaujolais and Bourgogne regions, where whole-bunch vinification – which can increase the release of astilbin – is practised. So, the effect of the addition of stems during vinification was also studied.
'The addition of stems during vatting significantly increased astilbin concentration'This new research showed that the addition of stems during vatting significantly increased astilbin concentration. Furthermore, this increase varied according to the grape variety. Whereas the astilbin contents were lower in Merlot wines than in Pinot Noir or Gamay wines, the ratio between its concentration of wines from the two modalities was higher in Merlot than in Pinot Noir and Gamay. The localisation of astilbin in the different components of the bunch, depending on the grape variety, was also investigated to understand this difference better. Thus, a higher abundance of astilbin in stems than in skins was found in the Merlot variety, whereas for Gamay and Pinot Noir, the total quantity of astilbin in a bunch was located in equal proportions in stems and skins.
The experiments carried out in Bordeaux estates on vinified Merlot wines showed an increase in astilbin until the eighth day, when alcoholic fermentation had finished, for the “30% whole bunches” modality with a concentration reaching 8.7 mg/L. In the “destemmed” vat, the maximum astilbin content was measured at 6 mg/L on the sixth day of vinification. The difference calculated between the two modalities was 31% of the maximum content. For the second experiment in Bordeaux, the astilbin concentration stabilised at around 5 mg/L for the “destemmed” modality and 8.4 mg/L for the “30% whole bunches” modality around the 11th day of vinification, that is seven days before the end of alcoholic fermentation. Here, the percentage difference was estimated at 40%.
With regards to the experiments carried out in Bourgogne with Pinot Noir, astilbin concentrations in the wines stabilised from the eighth day, at around 26 mg/L for the “destemmed” vat and around 32 mg/L for the vat with “50% whole bunches”. For the vat with “30% whole bunches”, astilbin levels reached 31 mg/L at the end of alcoholic fermentation but decreased to 24 mg/L five days later, which was slightly lower than the concentration measured in the “destemmed” vat at the same stage. However, the difference between the “destemmed” and “50% whole bunches” modalities was 19%. In the second experiment in Bourgogne, the concentration in the “destemmed” vat stabilised at around 30 mg/L two days before the end of alcoholic fermentation. For the “50% whole bunches” vat, the content increased to 38.8 mg/L in the sample taken five days after alcoholic fermentation. On the 14th day, the concentration of astilbin in the “destemmed” vat was 26% lower than in the vat with “50% whole bunches”.
The experiments on Gamay wines carried out in the Beaujolais region confirmed the previous observations. Astilbin levels increased between the eighth and 11th day of vinification, that is, before the end of alcoholic fermentation. Wines from Plot A vinified in 2020 and 2021 contained higher concentrations of astilbin than those from Plot B in the corresponding modality and vintage. The maximum concentrations found were 46 mg/L for the “30% whole bunches” modality, 42 mg/L for the “15% whole bunches” modality and 38 mg/L for the “destemmed” modality. These concentrations were slightly higher than those measured in the Pinot Noir and much higher than those in the Merlot wines. However, the differences between the “destemmed” and “30% whole bunches” modalities were 17% and 6%, respectively, for Plots A and B in the 2021 vintage.
In general, these experiments demonstrated that the addition of stems during winemaking increased the content of astilbin in the wines, regardless of the grape variety. Furthermore, the difference in astilbin content between modalities with and without the addition of stems varied according to the grape variety. Moreover, the majority of the extraction of astilbin occurred during the first part of alcoholic fermentation. This compound was, therefore, released into the aqueous phase when the juice still had low alcohol levels. This is also the case for flavonols such as quercetin and kaempferol, whose levels increase gradually between the fifth and seventh day of fermentation. In addition, astilbin concentration in modalities without stems seems to reach its maximum faster than in modalities with stems. This could suggest that astilbin present in the skins was released before that present in the stems.
How does astilbin content vary in grape varieties?
To study the influence of the grape variety, the total concentrations of astilbin in the bunches were calculated. Bunches of Pinot Noir contained an average of 17.5 ± 7.2 µg/g fresh extract, significantly more than Merlot bunches, with 8.6 ± 2.3 µg/g fresh extract. The average content in Gamay bunches was between the two grape varieties, at 10.3 ± 1.9 µg/g fresh extract.
From a global perspective, the stems were, therefore, the component containing the most astilbin, around five times more than the skins in our study. Nevertheless, on the scale of a bunch, the constituents were found in different proportions. After the separation of each cluster, the mass of each component was measured and the average proportions of each component in relation to the overall mass of the bunch were calculated for each grape variety. Pulp was the main component of the bunch, accounting on average for 79.4% for Gamay, 71.6% for Pinot Noir and 78.8% for Merlot. It is followed by skins (12% for Gamay, 16.3% for Pinot Noir and 12.7% for Merlot), seeds (5.2% for Gamay, 6.9% for Pinot Noir and 5.5% for Merlot) and, finally, stems (3.4% for Gamay, 5.1% for Pinot Noir and 3.1% for Merlot).
The differential effect of the grape variety on the astilbin concentration was measured with and without stem addition. Astilbin concentrations were higher in Gamay and Pinot Noir wines than in Merlot wines. For Gamay, the average concentrations were 27.7 and 31.9 mg/L for the “destemmed” and “with stems” modalities, respectively, and for Pinot Noir, the concentrations were 23.9 and 30.3 mg/L for these two modalities. For wines with a majority of Merlot, the average concentration was 5.6 mg/L for the “destemmed” modality and 8.8 mg/L for the “with stems” modality. In comparison with the taste detection threshold, the mean value of astilbin concentration with the addition of stems in Merlot wines exceeded this threshold, which was established at 5.7 mg/L. Finally, the addition of stems provided an average increase of 4.1 mg/L, 6.3 mg/L and 3.2 mg/L of astilbin for wine made from Gamay, Pinot Noir and Merlot, respectively.
Nevertheless, it is interesting to note that the difference in astilbin proportion between the two methods (“destemmed” and “with stems”) appeared to be greater for Merlot than for Gamay and Pinot Noir. In fact, the presence of stems during vinification contributed an average of 36% more astilbin for Merlot, compared with 21% for Pinot Noir and 12% for Gamay.
Does astilbin only come from stems?
No, the study also measured astilbin concentration in the various parts of the bunch, namely the stems, skins, seeds and pulp, and the differences between the grape varieties.
The results showed that the addition of stems during vatting significantly increased astilbin concentration. Furthermore, this increase varied according to the grape variety. Whereas the astilbin contents were lower in Merlot wines than in Pinot Noir or Gamay wines, the ratio between its concentration of wines from the two modalities was higher in Merlot than in Pinot Noir and Gamay.
The localisation of astilbin in the different components of the bunch, depending on the grape variety, was also investigated to understand this difference better. Thus, a higher abundance of astilbin in stems than in skins was found in the Merlot variety, whereas for Gamay and Pinot Noir, the total quantity of astilbin in a bunch was located in equal proportions in stems and skins.
This means that for a bunch of Gamay and Pinot Noir, the proportion of astilbin came half from the stem and half from the skins, whereas for Merlot, two-thirds of the total astilbin in a bunch was found in the stem.
How else do stems affect the composition of the wine?
The average pH was calculated at 3.46 ± 0.04 for the destemmed wines and 3.52 ± 0.04 for the ones with stems. Concerning the average alcohol content, it was calculated at 13.79 ± 0.82% for the destemmed modality and 13.68 ± 0.84% for the with-stems samples. The difference between these modalities was not significant.
Other studies have found the alcoholic degree lower in wines vinified with stems than in wines made from totally destemmed clusters. This difference is generally explained by the composition of the stem, which is rich in water and low in sugars. The water in the stems may dilute the must, while the ethanol formed during alcoholic fermentation is absorbed by the stems. In addition, some studies have described a decrease in acidity in wines made with stems due to the high potassium content of the stems, which can precipitate with tartaric acid. But, generally, these observations were made on wines for which all the stems were kept during vinification. The impact of a low proportion of stems (no more than 50% of whole bunches) on these parameters was measured in the new study, which discovered that adding between 15 and 50% of stems during vinification “did not seem to have any effect on pH or alcoholic strength”.
What’s the influence of the vintage?
The influence of vintage on astilbin contents in wines and stems from the same terroir was also studied. During the 2019, 2020 and 2021 vintages, samples of Pinot Noir stems were taken from nine different plots at an estate in Bourgogne. The average concentration for the 2020 vintage was measured at 2 ± 0.4 mg/g, almost double that of the 2021 vintage, measured at 1 ± 0.1 mg/g. For the 2019 vintage, the average concentration is 1.3 ± 0.3 mg/g.
In addition, astilbin levels were measured at the end of vinification in wines from the corresponding plots. The average astilbin concentrations of the 2019 and 2020 vintages, 43.8 ± 2 mg/L and 47.7 ± 3.9 mg/L, respectively, were significantly higher than those of the 2021 vintage (27.1 ± 1 mg/L). The 2021 vintage saw more rainfall and caused less water stress on the vines.
Click here to access the full study, ‘New insights about sensory contribution of grape stems during winemaking: role of astilbin, a sweet polyphenol’, which was published in OENO One, Vol. 58 No. 1 (2024).
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