Left out in the cold: Serving wines chilled

I like wine. In fact, when I initiated my doctoral studies, it was with the intention of becoming a winemaker. However, as a graduate student, I became less interested in how to make wine and more interested in the varied sensory experiences evoked by wines. Identical grapes grown in different environmental conditions can generate wines having very different sensory profiles. Similarly, the specific processing techniques a winemaker uses to create the wine will also greatly impact the product’s sensory attributes. In fact, there are numerous factors that influence a wine’s sensory profile and hence, its perceived quality. Of particular interest to the readership of Temperature is the effect of storage and serving temperature on the perception and liking of wine.

Storage and serving temperatures of wine serve different purposes. Ideal storage temperature, for both red and white wine, is about 13°C and allows for maturation while minimizing the risk of premature aging. Incidentally, 13°C reflects the nearly constant temperature observed in historic wine caves of France. Serving temperature, however, has evolved to optimize the sensory experience associated with wine consumption. For red wines, optimal serving temperatures are suggested to be 15–18°C, slightly below room temperature. For most whites and rosés, optimal serving temperature is 4–10°C, slightly above refrigeration temperature. See Box 1 for recommendations on storing and serving wine.

Box 1. Practical recommendations for storing and serving wine.

Storage of wines • Ideally store white, rosé, and red wines in a cool location (approximately 13°C) having minor temperature fluctuation (e.g. basement, wine cooler). Serving white and rosé wines • Chill white and rosé wines in refrigerator. Remove and set at room temperature for 30 mins before serving. Serving red wine • If stored at 13°C, serve as is. • If stored at room temperature, place red wines in refrigerator for 30 mins before serving.

With the warm summer months receding, many wine consumers are opting for temperate red wines instead of the chilled white wines. During the hot summer months, chilled white wines have cooling and thirst-quenching properties that many people find desirable. However, chilling also has profound effects on the sensory properties of the wine and what consumers actually perceive during consumption. Specifically, cooling a food or beverage reduces the release of volatile compounds that make up the characteristic “nose” and “flavor” of the particular product. In the case of wines, volatile, aromatic compounds are inhaled through the nose to produce the aromas that characterize particular grape varietals, regions, or treatments (e.g. aging in oak barrels). The wine descriptors are often defined in terms of associated sensory experiences, such as tropical fruit (e.g. banana) or floral (e.g. orange blossom) notes in the case of white wines, and berry (e.g. blackcurrant) and herbaceous (e.g. bell pepper) notes for red wines. Additional attributes characteristic of different wines have been identified and delineated in seminal work from Prof. Ann Noble in the development of the wine aroma wheel [1]. When consumed, the volatile compounds first enter the oral cavity where, upon swishing and swallowing the wine, they are pumped up the back of the throat, through the nasopharynx to the olfactory epithelium in the nasal cavity to elicit retronasal flavor perceptions. Although colloquially referred to as “taste”, these retronasal flavor sensations are highly important to the enjoyment of food and beverages. This is best demonstrated when considering how the sensory profiles are significantly altered when the nose is plugged, for instance when sick with a cold or when pinching the nostrils shut. Water-air and/or ethanol-air partition coefficients reflect the solubility of aroma compounds in each of these media and describe the propensity of volatile molecules to escape from the beverage into the headspace above the liquid. Partition coefficients are temperature dependent; as wine is chilled, the kinetic energy of aroma molecules is reduced, thus leading to fewer aroma compounds in the headspace. Such an effect will reduce the overall intensity of the perceived aroma and flavor compared to when that same wine is evaluated at room temperature. Moreover, temperature has a differential effect on the partition coefficients of different compounds. Consequently, the chemical fingerprint – the concentration of the various volatile molecules relative to one another in the headspace – will differ when analyzed at cold or warm temperatures. A different volatile fingerprint will elicit different aroma and/or flavor sensations in the assessor. The changes can be subtle or great depending on the specific flavor molecules and the temperature differences of the wines. When consuming chilled wines, many connoisseurs will aerate the wine in their oral cavity by swishing the bolus around in their mouth. Such an effect not only causes a greater release of the volatile compounds due to agitation, but will also warm the wine bolus, which also results in the release of flavors into the oral cavity. Thus, the flavor perceived from a chilled wine can effectively be enhanced by suitable manipulation within the mouth.

In addition to characteristic aromas, wines also elicit taste and, in some cases, astringent and irritant, or “hot”, sensations. Taste sensations are evoked by water soluble compounds and described as sweet, salty, sour, bitter, and umami. Although salty and umami are not often used to describe wines, winemakers will go to great lengths to find the appropriate balance of sweetness, sourness, and bitterness. Interestingly, taste sensations also seem to be temperature-dependent, although the effects are variable and often compound-specific. In general, taste sensitivity is greatest with stimulus temperatures between approximately 20 and 34°C [2]. Thus, sweetness, sourness, and bitterness will often be perceived as less intense when wines are chilled. Additionally, for some tastants, adaptation (the sensory phenomenon in which perceived intensity decreases with constant stimulation) is also temperature-dependent. Warming appears to slow adaptation to sweet, but not to bitter solutions [3] resulting in a more prolonged and intense sweet sensation. Combined, these effects may underpin the common practice of chilling very sweet wines or poor quality wines that are unbalanced in taste profile. Nevertheless, as with aroma, the typical practice of manipulating the wine in the mouth during evaluation will have a tendency to warm the liquid, thereby minimizing the effect of cooling.

Although also perceived in the mouth, astringency and irritation are not tastes. In wine, astringency is the rough or drying sensation that occurs when tannins interact with salivary proteins to reduce lubrication within the oral cavity, whereas irritation is the burning sensation elicited by high concentrations of ethanol. Both astringency and irritation are temperature-dependent. Chilling reduces perceived astringency albeit the effects are fairly small [4]. Suppression of astringency may be due to (a) decreased solution viscosity of the refrigerated solution, (b) a higher salivary flow rate in response to cold solutions, or (c) reduced tannin-protein interactions resulting from colder temperatures. Solution viscosity, salivary flow rate, and the degree of protein-compound interaction have all been shown to affect perceived astringency. When some wines (particularly red varietals) are consumed above optimal serving temperatures, connoisseurs will often characterize them as “hot”. This “hot” sensation is typically evoked in wines with relatively high alcohol content. Ethanol elicits this sensation by activating a temperature-sensitive receptor (TRPV1) normally responsive to hot temperatures [5]. Cooling reduces the likelihood of TRPV1 being activated. Not surprisingly, chilling a wine therefore, will decrease the activation of TRPV1 by ethanol and consequently reduce the “hot”, irritant sensation from the wine.

I like wine. The diversity of sensory experiences evoked by different grape varietals and processing techniques is impressive. That serving temperature further modifies the experienced sensations makes the consumption of wine even more enjoyable. Whether your preferred wine is red, white, or rosé, try serving them at different temperatures and experience the impact for yourself. À votre santé!