Wine, especially red wine is a complex mixture of water, ethanol, and thousands of organic compounds which helps in its aroma, taste, and mouthfeel and acts as a key factor in the sensory experience and price of wine. Astringency is a central element of mouthfeel and is perceived as a “dryness” or “puckering” sensation on the palate. Managing astringency is essential in winemaking as excessive levels can overpower the wine and too little can leave it tasting dull. Astringency arises from tannins which are compounds of grape skins and seeds that contain flavan-3-ols like catechin and epicatechin that polymerize into tannin chains of varying structures. Wine’s mouthfeel encompasses of various other sensations such as astringency, body, warmth, pricking, balance, burning, and viscosity. These tactile sensations arise from oral-tactile stimulation and are significant to wine perception as its appearance, aroma, and taste, though they are not yet fully understood. Wine mouthfeel can be studied using instrumental techniques focused on fluid behavior and frictional forces. In this article we will explore the wine components that contributes to wines mouthfeel sensations.
Figure-1 Summary of the wine components, mouthfeel and probable instrumental measurements [2]
Wines generally have an alcohol content ranging from 11% to 14%, though it can drop to 7.5% in certain botrytized wines or exceed 15% in some red and dessert wines. Ethanol in wine stimulates sensory and trigeminal pathways, creating lingering sensations of heat, bitterness, and viscosity, which add to the wine’s complexity. Density of ethanol correlates with alcohol content and dry extract in the wine but not with reducing sugar content and it decreases slightly at higher temperatures. Whereas, the viscosity depends on temperature, following an exponential relationship and at higher temperatures it leads to lower viscosity, impacting the mouthfeel. Wine “tears,” commonly used as a visual indicator of alcohol content, form inside the glass as volatile alcohol evaporates, increasing the surface tension of the wine coating. Due to the higher surface tension of water (72 dyne/cm) compared to ethanol (23 dyne/cm), droplets form and fall along the film toward the wine meniscus. Glycerol, with its high surface tension (63 dyne/cm), may also contribute, although its impact is understudied. While commonly observed, these tears contribute minimally to sensory assessment or wine quality differentiation.
Glycerol in wine is traditionally linked to sensory attributes like oiliness, persistence, and mellowness. Researchers have explored glycerol, ethanol, and sugar’s roles in perceived viscosity and density in model white wines. They found that while each compound influenced these perceptions, glycerol had no detectable effect below 25 g/L—a concentration much higher than typically present in red wines. In contrast, ethanol impacted perceived viscosity and density even at lower concentrations (0, 3, 7, and 10 g/L). The primary purpose of glycerol found in wine is for sweetness.
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Phenolic compounds, or polyphenols, in wine consist of an aromatic ring with hydroxyl groups. They are categorized into two main groups—flavonoids and non-flavonoids—which significantly influence taste and mouthfeel. The total phenolic content in wine is affected by factors like grape variety, growing conditions, harvest timing, and winemaking methods. Astringency in wine arises from various compounds, including metals, polyphenols, alcohols, and organic acids, but is primarily linked to polyphenols. These polyphenols originate from two main sources: the grapes and oak barrels. From grapes, astringency is contributed by hydroxybenzoic and hydroxycinnamic acids, flavonol glycosides, flavan-3-ols (procyanidins), and stilbenes. Oak barrels contribute hydrolyzed tannins, which also enhance astringency.
In addition to polyphenolic compounds, red wines contain significant macromolecular fractions such as polysaccharides. These are derived from various sources, including yeast cell walls (notably mannoproteins from Saccharomyces cerevisiae), grape cells (like arabinogalactan-proteins), and other microorganisms (e.g., bacteria). Polysaccharides enhance wine’s sensory characteristics by stabilizing flavor, color, and foam.
Figure-2 The interactions of wine polysaccharides with aroma compounds, tannins, and proteins, and their importance to winemaking [3]
In summary, highlights the various components that contribute to different mouthfeel sensations in wine. Astringency is primarily attributed to polyphenols, while ethanol and acidic polysaccharides can mitigate this sensation. Regarding the perception of fullness or body, polysaccharides appear to have a greater impact than alcohol, though comparative studies are lacking. Perceived viscosity is influenced by ethanol concentrations, but the roles of other components and their interactions remain unstudied. Minor components like proteins may also affect mouthfeel by interacting with polyphenols. Finally, previous studies have linked glycerol to oiliness sensations, suggesting its potential role in mouthfeel.
