The state of phenolic compounds is one of the most critical considerations in red wine production. The quantity and condition of phenolic compounds in wine profoundly influence its flavor profile. When phenolic compounds are present in insufficient quantities, the wine becomes easier to drink but inevitably appears diluted in color, taste, and nuance. Conversely, when phenolic compounds are excessively abundant, the wine develops overpowering bitterness and astringency that compromises drinkability.
Principal Phenolic Compounds in Red Wine
The most prominent phenolic compounds in red wine are anthocyanins, which influence color intensity, and tannins, which affect astringency. These two components have been so deeply implicated in quality assessment that wines exhibiting intense color and smooth tannins have historically been regarded as superior red wines.
Mechanism of Astringency from Tannins
The sensations described as bitterness or astringency arise when tannins bind to proteins that form the mucous membranes in the oral cavity upon wine consumption. It is now well established that tannins generate astringency by binding to mucin present in saliva.
When astringency is perceived intensely, the tannins are described as harsh. Conversely, when only mild astringency is perceived, the tannins are typically characterized as smooth. From a more chemical analytical perspective, the distinction between harsh and smooth tannins is explained by tannin reactivity.
When tannins in wine possess high reactivity, they rapidly bind to greater quantities of proteins, intensifying the astringency perceived in the oral cavity. Conversely, when tannin reactivity is low, the quantity of protein binding decreases, thereby reducing astringency. As a general tendency, decreased reactivity is more readily perceived organoleptically as smoothness.
Theoretical Foundation of Protein Fining
From this understanding, if smoother tannins receive higher evaluations, the logical conclusion is to reduce tannin reactivity. This concept forms the basis of protein fining in its contemporary sense.
Protein fining is a winemaking technique in which proteins are added to wine to bind with and remove tannins present in the wine. In the mechanism of astringency perception, tannins introduced externally via wine into the oral cavity, where proteins already exist, remove proteins. Protein fining performs precisely the same process in reverse. By adding proteins externally to wine where tannins already exist, the process induces proteins to remove tannins.
When the total quantity of tannins in wine decreases, the stoichiometric ratio between tannins and their binding partners changes. As a reduced quantity of tannins reacts with numerous substrates, the remaining tannins in wine undergo multiple reactions including polymerization and association. Consequently, the reactivity of residual tannins decreases. As a result, harsh tannins transform into smooth tannins.
The most widely recognized method of protein fining in wine is the use of egg whites. Since egg white fining does not utilize egg yolks, the famous anecdote relates that canelés were created to consume the remaining yolks.
Contemporary Challenges in Implementing Protein Fining
Although protein fining is employed to obtain smooth tannins—so-called silky tannins—implementation has become increasingly difficult in recent years for multiple reasons. The fact that albumin contained in egg whites is an allergen, the trend toward avoiding animal-derived proteins, and the rise of natural wine approaches that eschew oenological intervention have complicated the selection of protein fining as a winemaking option.
Limitations of Natural Transformation
Because phenolic compounds and tannins are highly reactive compounds, reactions proceed spontaneously over time even without external intervention, reducing their reactivity. In this sense, it is theoretically possible to reach a similar state eventually given sufficient time, without deliberately adding proteins for fining. However, whether wines containing stable silky tannins can be produced without using fining agents is, unfortunately, not so straightforward.
Apart from the requirement for extended time to await natural tannin reactions, the outcomes differ between tannin removal by fining agents and tannin transformation through natural reactions. The critical factor is the identity of tannins’ binding partners.
When fining agents are used, tannins preferentially bind to the fining agents. Consequently, the proportion of binding to substances other than fining agents decreases. Conversely, when awaiting natural transformation, tannins precipitate while binding to various substances. In the natural reaction process, substances that would have remained in the wine when fining agents were used inevitably become lost through binding with tannins.
Furthermore, when fining agents are added, tannins are removed in sufficient quantities. That is, the reactivity that impedes smoothness is reliably reduced. Conversely, with natural reactions, the extent of tannin reaction cannot be controlled. The possibility exists that reactivity will not be sufficiently reduced even after years. When reactivity remains insufficient, the tannins remain in a state incapable of producing a silky impression.
Uncertainty in Quality Achievement Through Extended Aging
When tannins that have been aged for many years and continued reacting slowly in the bottle have sufficiently reduced their reactivity, silky tannins become perceptible in that wine. Conversely, extended aging requires considerable time and, moreover, whether the wine will truly become silky is not guaranteed. One perspective holds that the uncertainty and rarity of extended aging constitute value itself. However, it is also true that extended aging is not necessarily welcome when stable, consistent quality is desired.
Rationale for Fining Agent Use and Contemporary Options
To produce—or enjoy—red wines more consistently possessing the quality attribute of “silky tannins,” implementing protein fining represents a viable option. Recently, fining agents derived from 100% plant-based or fish-based proteins that do not use animal-derived proteins including albumin have become commercially available. Concerns directed at fining agents themselves are being resolved. However, what continues to persist is aversion to oenological intervention.
Restrictions on Fining Agent Use in Natural Wine
Although natural wine popularity has shown some moderation compared to its peak, natural wines remain considerably popular. While natural wines draw attention primarily for the absence of sulfur dioxide additions and fermentation by wild yeast, in many cases the use of fining agents is also prohibited. Additionally, because most fining agents require filtration after addition, fining agent use is restricted in natural wines from the perspective that they must be unfiltered.
Choice Between Winemaking Philosophy and Quality Attributes
There is certainly nothing inherently wrong with not performing protein fining. However, when choosing not to fine, winemakers may need to accept abandoning achievement of specific quality attributes in some cases. Consumers may need to accept forgoing the satisfaction of silky tannins.
From the winemaker’s perspective, the decision not to use fining agents possesses certain rationality. Although difficult, it is possible to design wines to age cleanly over many years and acquire silky tannins. Winemakers can pursue both winemaking philosophy and quality assurance. Even if the decision not to use fining agents results in some loss of tannin silkiness, winemakers can accept this as a consequence of their decision.
However, the consumer’s position differs. If winemakers abandon pursuit of silky tannins, consumers can no longer reliably enjoy those flavors regardless of their desires.
Questions Regarding Market Sustainability
When empathy with winemaking philosophy is central to purchasing motivation, no problem arises if that support continues long-term. However, people’s interests and values are transient and may not be as sustainable as satisfaction with flavor itself. Wines that prioritize empathy with winemaking techniques while reducing flavor certainty may fail to acquire new supporters based on flavor alone when that empathy diminishes.
Can wines prioritizing winemaking philosophy sustain market support beyond the time required for tannins to acquire sufficient smoothness? Our current era poses questions to all of these: winemakers’ convictions, consumers’ preferences, and wine quality standards themselves. Perhaps only time can ultimately provide the answer.
