For this study, grapes were harvested at two different ripeness levels-25.4° Brix and 29° Brix-and then transported to the winery and vinified. At the winery, a large-scale, high-power ultrasound system was used to treat the less ripe grapes just after crushing. There were three different vinifications that were macerated with the skins for seven days.
At bottling, the wine was analyzed for aromatic compounds as well as its physicochemical, chromatic and sensory characteristics. The results showed that the wine produced from the ultrasound-treated grapes had very similar characteristics to the wine produced from the less ripe grapes, especially in terms of total tannin and total phenolic content, but with an alcohol content that was 15% lower than the latter.
The results of this project indicate that this technology can be applied to grapes to promote the extraction of phenolic compounds, even before the phenolic maturity of the grapes has been completed, allowing the production of quality wines with a reduced alcohol content.
Color, one of the most important quality attributes of red wine, depends on the phenolic composition of that wine. Color components not only provide the color of the wine but also add to the body and texture. Color is, therefore, closely related to the phenolic composition of the grapes. Grape phenolic compounds, both anthocyanins and tannins, are mainly located in the skins. Primarily, tannin compounds are concentrated in the seeds as well, and all are extracted into the must during crushing and maceration.
Although some oenological techniques can help extract these compounds, this extraction can be severely limited by the grape cell walls where these compounds are located. The cell wall forms a barrier to extraction. If these cell walls are not easily broken, the extraction of phenolic compounds will be limited. From this understanding of the grapes' development, phenolic maturity is identified as the stage where the phenolic content of the skin is not only high but also easily extractable.
The difficulty when it comes to extracting the tannins from the seeds is also reduced due to the lignification of the seed. When grapes are phenologically-immature, phenolic compounds from the skin are not easily extracted, even when present at high concentrations, and yet high concentrations of astringent tannins from the seeds may be present. This situation changes upon reaching phenological maturity-when cell walls are easily degraded, and phenolic compounds are extracted.
What does the EU-UK reset mean for wine?
Choosing the optimal time for harvest has generally been based on when a variety is well adapted to its terroir and technical maturity is reached (defined as an optimal level of sugar content in grapes for that grape variety). This also requires that the grapes' phenolic and aromatic maturity (i.e., when grapes have lost vegetal, herbaceous and fruity aromas) are reached at the same time.
Climate, however, exerts a major influence on vine phenology and grape composition. Among the most important effects related to climate change is vine phenology modification. If grapevine phenology is shifted to earlier dates, due to global warming, this indicates asynchronous development of grape composition. Sugar accumulation is faster than phenolic compound synthesis. Consequently, harvest is delayed, allowing the grapes to reach higher sugar levels in the berries than previously desired. The delay was thought to be necessary because optimal aromatic and phenolic ripeness was more important to wine quality than alcohol concentration. Alcohol removal is now the leading solution to this issue.
The problem of high-alcohol wines is a major concern for winemakers as it has potential implications for wine quality. Ethanol is sensorially important for wine and indispensable for the stability, aging and organoleptic properties of wine and, therefore, for wine style. However, higher concentrations of ethanol are not necessary or desirable for many reasons. Ethanol can have deleterious effects on the cells of the yeast and it can also be harmful to the taste of the wine. The fermentation process may become slow or stuck, and high ethanol can also inhibit malolactic fermentation. From a sensory point of view, ethanol influences perceptions of astringency, acidity, flavor and aroma. High ethanol has been perceived as warmer on the palate. Our industry is also responding to a perception that high-alcohol content has a negative effect on human health. In addition, in some specific locations, higher ethanol content may be more expensive as in many countries it is taxed at higher rates.
In view of all these problems, winemakers are looking for possibilities to obtain high quality wines with reduced alcohol content. Different approaches have been proposed to reduce alcohol levels in wines at all stages of the winemaking process, from the addition of unripe grape juice to finished wines to the use of yeasts with a low-alcohol yield, or the use of technologies to carry out partial dealcoholization.
The easiest solution for alcohol reduction in wine would be to harvest grapes at a lower sugar content, though one would have to take into consideration and address the grapes' phenolic compound maturity at this earlier phenotypic stage. Plus, there is the requirement to obtain deep-colored wines. Some oenological techniques focus on this problem, such as the use of maceration enzymes or pre-fermentation maceration techniques, or novel technologies, like Della Toffola's ACE (which has been reported in the January 2025 issue of WBM) that could be used to solve this problem. The novel technology to solve this problem is high-power ultrasound (HPU), technology approved for use by wineries by the International Organization of Vine and Wine (OIV) in 2019.
HPUs are generally made up of frequencies between 20 and 40 kHz with an energy level high enough to produce acoustic cavitation. This effect creates the formation of tiny bubbles that grow until they reach a critical size where their implosion occurs. During the implosion, considerably high temperatures and pressures were reached (about 5,000 K and about 2,000 atm, respectively). When this implosion occurs close to a cell, the resulting sound waves impact and break the cell walls, leading to two potential outcomes: in plant cells, it allows the diffusion and release of the compounds located inside the cell; in the case of microorganism cells that might be present on or in the grape, it can lead to cell rupture, destroying the organism.
In enology, HPUs can be used to: 1. Improve the extraction of phenolic and aromatic compounds from grapes. 2. Reduce the use of SO2 by reducing microbial counts. Other researchers have concluded that high-power ultrasound applied in a continuous flow showed a satisfactory reduction of Brettanomyces yeasts (89.199.7%) and lactic acid bacteria (71.8-99.3%). This supports a hypothesis that ultrasound at various stages of winemaking is good for wine preservation. 3. Age wines on lees combined with ultrasound and non-Saccharomyces strains to accelerate aging to study impacts on polysaccharide release and on the organoleptic properties of red wine. Others have tested the effects of HPUs during wine aging on lees and concluded that their effect could be compared to the use of β-glucanase enzymes capable of demolishing lees' glucans and facilitating the release of intracellular components. 4. Recover secondary products such as phenols from grape pomace or stilbenes from grape shoots.
The acceleration of aging reactions is another effect of cavitation and has caused the production of highly reactive radical species, such as OH-and H+ radicals that can undergo a range of subsequent reactions, including the generation of H2 O2 . These highly oxidizing species can have a significant effect on both biological and chemical species in aqueous solutions. The possible formation of free radicals could help accelerate wine aging reactions. Knowing this effect of HPUs, others have found the first direct evidence of the formation of the free radical 1-hydroxylethyl (a radical arising from the oxidation of ethanol) in red wine exposed to ultrasound and have claimed that ultrasound treatment can accelerate some aging reactions and shorten the aging period of wine. Consequently, ultrasound not only temporarily influenced the chromatic characteristics and phenolic composition of wine but also had a longer lasting effect on their evolution during wine storage.
In this work, the interest is focused on the effect HPUs may have on facilitating the reduction of alcohol in intensely colored wines by applying HPU to crushed grapes with a lower sugar content. The experiments that were conducted utilized small-scale quantities of about 400 kg where two batches of the same grape variety were grown in the same vineyard, but one location achieved a higher Brix than another location on the same day. The two Brix levels (25.4° and 29° Brix) were subjected to seven days of maceration. The grapes were separated into three fermentations: A control with no HPU; the second with the lower Brix level and HPU; and the third with the higher Brix level and no HPU. Standard winemaking techniques were used. The HPU chosen was 28 kHz with a power density of 8 W/cm2 .
Test materials are identified as C14 (control low sugar), US 14 (HPU treated low sugar) and C16 (control high sugar). After fermentation, the normal aspects of wine chemistry were determined, including alcohol content, pH, total and volatile acidity, acetic acid, reducing sugar, methanol, malic acid and tartaric acid, ethanol and gluconic acid, as part of this evaluation (see published paper for the detailed results). Spectrophotometric analyses were evaluated at 620, 520 and 420 nm, with the standard ratios of absorbances.
The US14 wine samples were in the negative part of component 2, and the C16 wine sample was in the positive part. The descriptors with the highest loads in the negative part of component 2 were astringency, total tannins (determined by phloroglucinolysis), galloylation percentage and aroma quality, which largely coincide with the observed results of the analytical variables. These analyses clearly indicate that the use of HPU induces a modification in the composition of the wine, especially the chromatic composition and sensory characteristics, leading to a wine that shares more characteristics with the wine made from the ripest grapes while maintaining a lower alcohol content.
Conclusion
The results showed that the wine obtained from ultrasound-treated grapes had chromatic characteristics that did not differ from those obtained from riper grapes and achieved the highest scores in the aroma and texture quality descriptors in a sensory analysis. The use of ultrasound technology, as a clean, ecological and energy-efficient technology (and no less important, being an authorized practice in wineries), could be an interesting option to obtain wines with parameters of color intensity and sensory quality similar to wines obtained from riper grapes but with a lower alcohol content.
Final Comment
While at the SIMEI conference in Milan, Italy in 2024, I was able to taste the wines that were discussed in this article. My assessment is that this type of technology can be a significant improvement for grapes grown in cooler climates with more variable weather to overcome. To their credit, Agrovin is working hard to find ways to get this important technology to wineries located in places that need this type of assistance.
