By: Denise M. Gardner
In previous blog posts, we covered an introduction to what anthocyanins (red wine color pigments) are and how they can be stabilized in wine. Additionally, Marlena Sheridan recently discussed current research on acetaldehyde-bridging amongst anthocyanins or anthocyanin and tannin substances in wine.
This post will evaluate several techniques used during red winemaking, and what the scientific literature has found regarding their impact on red wine color stability.
Anthocyanins undergo three main phases during the course of a wine’s life:
- Development in the grape
- Extraction during primary fermentation
- Stabilization through the life of the wine
While vineyard development is an important aspect of color stabilization, as starting anthocyanin concentration will ultimately determine potential processing decisions for winemakers, the following processes are reflective of winemaking techniques believed to affect red wine color stabilization. As you siphon through the various techniques, please remember that there is no one fix-all solution to improve red wine color stability. Wine is a complex matrix, and results may vary from one variety to the next, or from one vintage to the next.
Cold soak is a pre-fermentation process in which grape must is held at low (≤10°C, ≤50°F) temperatures. There are various ways to execute a cold soak step in wine production:
- Placing a holding vessel (i.e., a macrobin) in a cool, ambient environment
- Use of tank temperature control
- Use of dry ice
Cold soaking grape must is believed to increase anthocyanin extraction pre-fermentation. Increasing anthocyanin extraction would make stabilization reactions more favorable, pushing equilibrium to building stable anthocyanin-complexes through and after fermentation.
However, several studies have investigated the use of cold soak on various red wine varieties. In two Pinot Noir studies (Gerbaux 1993, Feuillat 1996, Sacchi et al. 2005*), detrimental effects to color were found on Burgundian wines when cold soak was used pre-fermentation. Similarly, Heatherbell et al. (1996) found no difference in wine color for those wines that were cold soaked versus the non-cold soaked controls.
A study that tested freezing must, however, had a different impact on the finished wine color. The variety evaluated was Merlot, and musts were frozen with dry ice. An increase in anthocyanin concentration by 50% and increase in overall tannin concentration by 52% was found in finished wines in which grape must had been frozen pre-fermentation, compared to an untreated grape must, control wines (Couasnon 1999, Sacchi et al. 2005*). Freezing may have a greater effect on anthocyanin concentration, as freezing physically causes berry cells to burst and release its contents.
Practical Winemaking Application: Winemakers do not need to utilize a cold soaking step to increase anthocyanin extraction or improve red wine color stability, as most research suggests there is no effect regarding red wine color stability. However, it is important to note that little research has been conducted regarding potential extraction of phenol and/or tannin complexes (including polymeric pigment content) during the cold soak step.
Saignée is the French term for “bleed,” and is utilized as a winemaking technique for making rosé wines by “bleeding off” free-run juice from macerated red grapes. While the free-run juice may be used for rosé production, many winemakers utilize the saignée technique to concentrate (increase extraction) of anthocyanins and tannins in the juice that will be made into a finished red wine. Secondary effects may also increase flavor concentration.
In 1972, Singleton found that the use of saignée increased the flavonoid and anothocyanin concentrations in the concentrated red wine, four months post-fermentation. Gerbaux (1993) found slight increases in color (through sensory analysis) and phenolics of young Pinot Noir wines that had been subjected to saignée practices. However, unlike Singleton, Gerbaux’s study did not find increases in anthocyanin concentration. However, Gawel et al. (2001) found initial increases in anthocyanin concentrations at the end of primary fermentation in pressed Syrah wines, but these concentrations were depleted after 6-months post-fermentation. This study did not investigate the fate of monomeric anthocyanins, and depleted concentrations of anthocyanins were likely caused by potential polymerization or adsorption of anthocynanins onto various other wine constituents (e.g. dead yeast cells, tartrates).
Practical Winemaking Application: While the causes of potential increased color stability are unclear, the use of saignée to concentrate red grape must appears to have a positive outcome on the wine’s color stability properties. Currently, there is no evidence that removal of 10% free-run juice is less beneficial than removal of 20%. However, as saignée is a concentration method, if the grapes are of low quality, the winemaker will only concentrate other poor quality components (i.e. off-flavors, excessive tannin, etc.) with use of this technique.
Micro-ox is the “addition of dissolved oxygen at controlled dosage rates at or less than the oxygen uptake rate of wine” (Paul 2002). According to Dykes (2007), typical dosages rates range from 2 – 90 mg of oxygen per liter of wine per month. The utilization of micro-ox is believed to affect the stabilization of red wine color pigments, and therefore requires adequate starting material (i.e. anthocyanins, phenolics/tannins) in order for this method to be effective.
Theoretically, when used between primary fermentation and malolactic fermentation, the integration of dissolved oxygen should provide the chemical constituents needed to initiate polymeric pigment formation of monomeric anthocyanins. Micro-ox is used as a driving force to influence acetaldehyde concentration and influence acetaldehyde-bridged complexes previously described by Marlena Sheridan. One previous study has shown no rise in acetaldehyde contraction by use of micro-ox (Pozo et al. 2010). However, this study did find that wines subjected to micro-ox treatment did have an increased concentration of sulfite-resistant pigments. Many other wine experts have written on the use of micro-ox, and there is a world of scientific literature available regarding its use and outcomes in red wines, with varied guaranteed consensus. Additionally, micro-ox has potential to alter other characteristics of wines, including mouthfeel or flavor, in both positive and negative ways, which is often dependent on the starting wine chemistry. The extent of this summary does not nearly cover the depth of research regarding micro-ox in wine production, and will be tabled for a later date.
Practical Winemaking Application: The use of micro-oxygenation may be a powerful tool to enhance anothocyanin stabilization. Winemakers are encouraged to work with the unit’s supplier or a consultant with micro-oxygenation experience prior to implementing this strategy into processing procedures. Anecdotally, at Penn State, we have noticed little success of micro-oxygenation to improve red wine color when used on wines that have relatively low anothocyanin concentrations (<200 mg/L GAE).
Thermovinification is a technique that uses a brief heating step to grape must or juice, and subjecting it temperatures above 60°C (140°F). It is believed that thermovinification enhances both extraction and stabilization of anthocyanins.
Auw et al. (1996) found that the use of thermovinification increased the concentration of free, monomeric anthocyanins in both Cabernet Sauvignon and Chambourcin wines. Additionally, this study also found increased concentrations of phenolics in the Chambourcin wine treated with thermovinification pre-fermentation, and a lower phenolic content in Cabernet Sauvignon wines treated with thermovinification. This emphasizes that solutions to improve color stability may vary depending on the grape variety and its heritage (i.e. native variety vs. hybrid vs. V. vinifera). Additionally, Sacchi et al. (2005) also concluded that it is necessary to have some skin contact time with grape skins after thermovinification treatment in order to enhance extraction of anthocyanins.
Practical Winemaking Application: The use of thermovinification to improve red wine color stability may be a practical tool for red wines, especially those red wines with minimal aging requirement. Thermovinification is not recommended for red wines destined for long term aging. It should be noted that thermovinification may alter flavor of the finished wines. A winery should evaluate the potential sensory impact of thermovinification prior to committing all wines to this process.
Extended Maceration is the process of allowing skins and seeds in contact with the finished red wine, post-fermentation, for an extended period of time. Various studies researching the effects of extended maceration on red wines have found increased concentrations of tannins, especially tannins from grape seeds. However, this process has not been shown to increase extraction or concentration of anthocyanins.
Auw et al. (1996) found that a thermovinification treatment was more effective at increasing phenolic composition compared to extended maceration for Chambourcin wines, but that for Cabernet Sauvignon wines, extended maceration was more effective at increasing phenolic concentrations. Watson et al. (1994, 1995) also found an increase in flavanol and polymeric pigment extraction in Pinot Noir wines that underwent extended maceration.
Practical Winemaking Application: Extended maceration will not increase free monomeric anthocyanin concentrations. This practice should only be utilized for winemakers wishing to increase tannin-based extractions. For a review on why the effects of extended maceration may be focused on phenolic extraction, please see Dr. Anna Katharine Mansfield’s recently published article, “A Few Truths About Phenolics,” in Wines & Vines.
Delayed Malolactic Fermentation (MLF)
The most current scientific literature on delayed MLF is coming out of Dr. James Osborne’s lab in Oregon. This practice is literally as it sounds: winemakers allow a wine to finish primary fermentation and wait (without addition of sulfur dioxide) for a specific period of time until MLF progresses naturally or is inoculated. This is an anthocyanin stabilization processing technique.
On studies in Pinot Noir, James and Osborne (2014) found that a 200 day delay in MLF was required for wines that went through MLF to reach a similar concentration of polymeric pigment, statistically, as the control wine that did not undergo MLF. It is important to remember that in order to maintain stability of wines not treated with sulfur dioxide, adequate temperature control (i.e. maintaining the cellar at 50-55°F or 10-13°C) will cause polymeric pigment formation reactions to progress slowly, which may influence why so much time is needed in delaying MLF. While increase temperature would increase the rate of polymeric pigment formation reactions, the increase in temperature also puts wines at greater risk for microbial spoilage.
Practical Winemaking Application: The jury is not out on this practice! Although some winemakers swear this practice works, it is important to remember than many wineries do not run “control” treatments for various practices. As there is much vintage-to-vintage variation amongst wines, it is challenging to draw solid conclusions from commercial wineries that do not utilize a control treatment. Currently, the literature states a delay in MLF may effectively improve color, but the time required for that delay may not be practical from a commercial operation standpoint. Additionally, winemakers must maintain effective strategies at monitoring potential spoilage during a vulnerable period of time when the wine is not protected by preservatives (sulfur dioxide).
While this blog post covers several techniques believed to affect red wine color stability, the review article by Sacchi et al. covers several additional topics including: yeast selection, fermentation temperature, the effects of sulfur dioxide, carbonic maceration, the use of pectolytic enzymes, and utilization of pump-overs and punch downs during primary fermentation. The review of the current scientific understanding of these practices (up to research literature published through 2005) can be found in the American Journal of Enology and Viticulture (AJEV).
Sacchi et al. 2005* The following authors (Couasnon 1999, Feuillat 1996, and Gerbaux 1993) were included in the Sacchi et al. 2005 review article. As initial research article was in another language, information regarding these studies was obtained from Sachhi et al. 2005.
Auw, J.W., V. Blanco, S.F. O’Keefe, and C.A. Sims. 1996. Effect of processing on the phenolics and color of Cabernet Sauvignon, Chambourcin, and Noble wines and juices. Am. J. Enol. Vitic. 47(3):279-286.
Burns, T.R. and J.P. Osborne. 2014. Loss of Pinot Noir wine color and polymeric pigment after malolactic fermentation and potential causes. Am. J. Enol. Vitic.
Couasnon, M.B. 1999. Une nouvelle technique: La maceration préfermentaire à froid-extraction à la neige carbonique. Premiér partie: Résultats oenologiques. Rev. Oenol. 92:26-30.
Dykes, S. 2007. The effect of oxygen dosage rate on chemical and sensory changes occurring during micro-oxygenation of New Zealand red wine. Diss. Food Sci. Univ. of Auckland.
Feuillat, M. 1996. Vinification du Pinot Noir en Bourgogne par maceration préfermentaire à froid. Rev. Oenol. 83:29-31.
Gawel, R., P.G. Iland, P.A. Leske, and C.G. Dunn. 2001. Compositional and sensory differences in Syrah wines following juice run-off prior to fermentation. J. Wine Res. 12(1): 5-18.
Gerbaux, V. 1993. Etude: de quelques conditions de cuvaison susceptibles d’augmenter la composition polyphénolique des vins de Pinot Noir. Rev. Oenol. 69:15-18.
Heatherbell, D., M. Dicey, S. Goldsworthy, and L. Vanhanen. 1996. Effect of cold maceration on the composition, color, and flavor of Pinot Noir wine. In Proceedings of the Fourth International Symposium on Cool Climate Enology and Viticulture. T. Henick-Kling et al. (Eds.), pp. VI: 10-17. New York State Agricultural Experiment Station, Geneva.
Paul, R. 2002. Micro-oxygentation – Where now.” Australian Society of Viticulture and Oenology, Uses of Gases in Winemaking Seminar Proceedings.
Pozo, A.G., I. Arozarena, M.-J. Noriega, M. Navarro, and A. Casp. 2010. Short- and long-term effects of micro-oxygenation treatments on the colour and phenolic composition of a Cabernet Sauvignon wine aged in barrels and/or bottles. Eur. Food Res. Technol. 231: 589-601
Sacchi, K.L., L.F. Bisson, and D.O. Adams. 2005. A review of winemaking techniques on phenolic extraction in red wines. Am. J. Enol. Vitic. 56(3):197-206.
Singleton, V.L. 1972. Effects on red wine quality of removing juice before fermentation to simulate variation in berry size. Am. J. Enol. Vitic. 23:106-113.
Watson, B.T., S.F. Price, H.P. Chen, and M. Valladao. 1994. Pinot Noir processing effects on wine color and phenolics. Abstr. Am. J. Enol. Vitic. 45:471-472.
Watson, B.T., S.F. Price, and M. Valladao. 1995. Effect of fermentation practices on anthocyanin and phenolic composition of Pinot Noir wines. Abstr. Am. J. Enol. Vitic. 46:404.
By: Marlena Sheridan
Acetaldehyde is a compound found in wine that has a profound effect on color stability and astringency. Acetaldehyde reacts directly with red wine tannins and anthocyanins to form polymeric pigments and modified tannins. Denise has already provided a great review of polymeric pigment formation (see her post form March 6, 2015). Here, I’ll be focusing on the reactions involving acetaldehyde and research we’ve completed on the topic.
Acetaldehyde reacts with tannins and anthocyanins to form irreversible, covalent bridges. When these reactions are between tannins, they can alter the structure so that its shape and activity are changed. This affects wine astringency, a mechanism based on the interaction of tannins and salivary proteins. Modified tannins, including acetaldehyde-bridged tannins, have been shown to have lower astringency because of their structural changes (Gambuti 2013). A model of these reactions is shown in Figure 1. These changes contribute to the shift from drying or puckering mouthfeel to a more velvety mouthfeel in aged wines.
Similar reactions take place between anthocyanins and tannins as well as between anthocyanins themselves. These reactions form polymeric pigments: pyranoanthocyanins and vitisins (see Denise’s previous post; Cheynier 2006). A model for these reactions is shown in Figure 2. As Denise has covered, these polymeric pigments have increased stability to sulfite bleaching and pH changes compared to monomeric anthocyanins.
As has hopefully been made clear, using these reactions of acetaldehyde with tannins and anthocyanins is an important tool for winemakers. Winemakers can use several techniques to get the benefits of acetaldehyde on pigment and tannin structure. These use oxygen incorporation to form acetaldehyde through a series of metal-catalyzed reactions (Danilewicz 2003). Along this pathway, there is the possibility to form detrimental oxidation products instead of the desired acetaldehyde. A simplified version of this mechanism is shown in Figure 3. These other oxidation pathways can lead to some of the risks of oxygen exposure including the loss of desirable aromas, browning, and the formation of off odors.
Ideally, winemakers would be able to get the benefits of acetaldehyde without the risks of oxygen exposure. By adding acetaldehyde directly, we could avoid the problems of oxidation while simultaneously controlling the beneficial oxidation reactions we’re hoping for. With this in mind, we conducted an experiment where exogenous acetaldehyde was added during red wine fermentation using Cabernet Franc grapes from North East, PA.
The must was separated into three groups – control, low acetaldehyde, and high acetaldehyde. The acetaldehyde groups received four doses during the fermentation, 4×25 mg/L acetaldehyde in the low group and 4×250 mg/L acetaldehyde in the high group. Fermentations were performed in quadruplicate in microfermenters (Figure 4). Wines were fermented to dryness and pressed prior to analysis.
Wines were analyzed for color stability by the modified Somers assay (Mercurio 2007) with measures of sulfite-resistant pigments, or polymeric pigments, shown here. Astringency was measured using a model protein precipitation, where wines were mixed with bovine serum albumin (BSA) and the amount of tannin precipitated was quantified (Mercurio 2008). Higher tannin precipitation implies higher astringency. Data from this experiment is shown in Figure 5.
As shown in Figure 5, there was a statistically significant decrease in the measure of astringency and increase in color stability with high acetaldehyde treatment. This data provides evidence that exogenous acetaldehyde can be used in red wines to get beneficial effects on color and astringency without oxygen exposure. A more detailed discussion of the results can be found in the published manuscript (Sheridan 2015).
Based on this work, we are continuing to examine the reaction of acetaldehyde with tannins and anthocyanins. We are currently working with model wine experiments to further understand the chemistry of these reactions including characterizing the final products and the effect of wine composition.
Cheynier, V. & Dueñas-Paton, M. Structure and properties of wine pigments and tannins. Am. J. Enol. Vitic. 2006, 57, 298–305.
Danilewicz, J. C. Review of Reaction Mechanisms of Oxygen and Proposed Intermediate Reduction Products in Wine : Central Role of Iron and Copper. Am. J. Enol. Vitic. 2003, 54, 73–85.
Gambuti, A., Rinaldi, A., Ugliano, M. & Moio, L. Evolution of phenolic compounds and astringency during aging of red wine: effect of oxygen exposure before and after bottling. J. Agric. Food Chem. 2013, 61, 1618–27.
Mercurio, M. D., Dambergs, R. G., Herderich, M. J. & Smith, P. A. High throughput analysis of red wine and grape phenolics-adaptation and validation of methyl cellulose precipitable tannin assay and modified Somers color assay to a rapid 96 well plate format. J. Agric. Food Chem. 2007, 55, 4651–7.
Mercurio, M. D. & Smith, P. A. Tannin quantification in red grapes and wine: comparison of polysaccharide- and protein-based tannin precipitation techniques and their ability to model wine astringency. J. Agric. Food Chem. 2008, 56, 5528–37.
Sheridan, M.K. & R.J. Elias. 2015. Exogenous acetaldehyde as a tool for modulating wine color and astringency during fermentation. Food Chem. 2015, 177, 17-22.
By: Denise M. Gardner
Chemical Structure Figures By: Marlena Sheridan
Red wine color stability has been an important issue identified by the Pennsylvania wine industry during the 2013 and 2014 harvest seasons. It is likely to be a continuing issue for years to come. However, it should be noted that color stability issues are not localized to the Pennsylvania region.
To comprehend problems affiliated with red wine color stability, an understanding of the components that are currently known to contribute to red wine color is essential.
The phenol, a single benzene ring, is the chemical building block that contributes to many components affiliated in wine. Chemically, it is characterized by a hydroxyl group (-OH) attached to a benzene ring.
Two classes of phenolics, flavonoids and non-flavonoids, contribute to wine color. For the purpose of this discussion, we will focus on flavonoids, which are defined by containing 3 phenolic rings in their chemical structure, shown below.
There are several sub-classes within the flavonoid class that contribute to red wine pigmentation. This review will focus on 3 of these subclasses:
- Flavan-3-ols (Catechins)
- Tannins (Proanthocyanidins)
Each one of these structures will contain the 3-phenolic ringed flavonoid backbone in their chemical structure (Figure 3). Variation of these subclasses exists with regards to attached units to the flavonoid backbone.
When reading the literature, understanding phenolic chemistry can become confusing, as many words like “tannins” can be used interchangeably with other terms (such as “proanthocyanidins,” “condensed tannins,” or “anthocyanogens”). This can be a daunting challenge for winemakers that are not proficient in chemistry-based terminology. Asking wine chemists for an explanation or clarification of terms is perfectly acceptable.
Anthocyanins are the red pigment compounds, or chemical structures, that primarily contribute to wine color. Actually, anthocyanins can reflect a number of red-blue hues, often dependent on pH. There are many types of anthocyanins that are identified in grapes (e.g. malvidin, cyanidin, etc.) that are also present in other fruits. It’s important to note that much of the research to date is focused on malvidin-3-glucoside as it is the anthocyanin in highest concentration in Vitis vinifera species (with exception to Pinot Noir) and most easily accessible in a pure form, which makes it easy to obtain for research purposes.
However, many French-American hybrid varieties and native varieties (like Concord) typically contain a different anthocyanin profile in which malvidin-3,5-diglucoside may not be the primary anthocyanin (Ribéreau-Gayon 1959). Many hybrids and native varieties have a higher concentration of other diglucosides or acylated anthocyanins (Hrazdina and Franzese 1974, Ingalsbe et al. 1963). Acylated anthocyanins are often recognized for their contribution to “hybrid red wine character” as their expressed color falls in an orange to light red/pinkish hue (Mansfield 2015). [Note: the term “diglucoside” indicates that there are 2 (di-) sugar (-glucoside) units attached to the malvidin anthocyanin.]
Monomeric anthocyanins, or “free” anthocyanins, are noted for their susceptibility to bleaching by sulfur dioxide or to a change in hue due to a shift in pH. At wine pH (~3.4), only 10% of the monomeric anthocyanins exist in a state that expresses red color (i.e. the flavylium ion) (Somers and Evans 1974). Research has found that the majority of the monomeric anthocyanin exists in the hemiacetal structure, which is actually colorless (Kennedy et al. 2006). This is why anthocyanin concentration does not exactly reflect color intensity or color density of the wine.
Anthocyanin extraction occurs early in fermentation (Kennedy et al. 2006), and is usually at its maximum concentration by day 4 into primary fermentation (Mansfield 2015). Throughout the duration of primary fermentation, the concentration of monomeric anthocyanins will decrease by 10-20% due to insolubility in ethanol and adsorption by wine yeasts/lees (Kennedy et al. 2006).
Flavan-3-ols, also known as catechins, are found primarily in grape seeds (Kennedy et al. 2006). These components are large contributors to wine bitterness, but may also contribute to astringency at a lesser extent (Kennedy et al. 2006). In contrast to anthocyanins, monomeric flavan-3-ol concentrations tend to increase throughout the duration of primary fermentation (Kennedy et al. 2006). This is predominantly due to the increased allowable extraction time as seeds are in contact with the ethanol environment.
Tannins, or proanthocyanidins, are polymers of favan-3-ol monomeric units. Tannins are responsible for the wine’s astringency, and are extracted from grape skins, seeds, and green matter (i.e. stems) (Kennedy et al. 2006). Tannins can also develop through the age of the wine by polymerizing monomeric favan-3-ols. Tannin extraction directly from the grape matter also appears to increase with longer skin/seed contact time during primary fermentation.
However, tannin extraction and utilization may also be variable in non-vinifera varieties. A recent study by Springer and Sacks (2014) from Cornell University found that many hybrid varieties actually contain higher concentrations of tannin-binding proteins inherent to hybrid variety’s disease- and cold-hardiness resistance. This could explain limited tannin extraction capabilities often affiliated with hybrid red wines. Additionally, if those proteins remain in the wine through primary fermentation, exogenous tannin additions may immediately bind to those proteins. Protein binding to exogenous tannins may minimize their chemical or sensory impact on hybrid wines.
Color Pigment Complexing: Copigmentation
Copigmentation describes an interaction between an anthocyanin and non-colored substrate (often referred to as a “copigment”) that enhances red-blue color hues of young red wines (Boulton 2001). Copigmented complexes are linked non-covalently. I like to think of this as the human equivalent of two individuals linking arms: the unit of 2 can still act as one, but can also easily separate.
The non-colored substrates affiliated with copigmented complexes include monomeric phenols (Figure 2), cinnamic acids, quercitin glycosides, vitexin, and orientin (Boulton 2001). Tannins play an extremely minor role in copigmentation (Boulton 2001).
It should be noted that some white grape varieties are believed to contain higher concentrations of non-colored substrates compared to many red wine varieties (Boulton 2001). Therefore, the act of blending 10-15% of a white grape variety (or white grape skins and seeds) to a red wine fermentation is believed to enhance the potential for copigmentation formation. Essentially, the concentration of co-factors is increased to encourage substrate availability for copigmentation. Malvasia with Sangiovese or Viognier with Syrah are classic white-red fermentation blends used in Old World winemaking regions to enhance red wine color. This phenomenon does not work if the white variety has insufficient concentrations of non-colored substrates (Boulton 2001).
Copigmented complexes are mainly affiliated with young red wines, as they tend to cause a shift in hue from red to a purplish-red. These complexes are less susceptible to sulfur dioxide bleaching or changes in wine pH compared to monomeric anthocyanins.
Color Pigment Complexing: Polymeric Pigments
If the human equivalent of copigmentation complexes are two individuals linking arms, polymeric pigments can be thought of as two individuals each contributing one their individual legs into one pair of pants. This is because polymeric pigments are covalently linked anthocyanin-flavonoid complexes. (Recall that the term “flavonoid” can account for many other things such as another anthocyanin, tannin, etc.) Polymeric anthocyanin-anthocyanin pigments are known as vitisins (Kennedy et al. 2006).
Polymeric pigments can form under two different mechanisms. The first is through a direct linkage of an anthocyanin and another flavonoid substrate (Figures 4 and 5). In this case, the two units are covalently linked together. The image below details this using chemical structures and a schematic.
The second form of polymeric pigments is through acetaldehyde-bridged complexes (Figures 6 and 7). In this situation, acetaldehyde, an aroma compound typically associated with wine oxidation, forms a link, or bridge, between the anthocyanin and another flavonoid substrate. This is detailed below using chemical structures and a schematic.
To make this topic even more confusing, the phenolic rings affiliated with anthocyanins and/or tannins can open and re-arrange within the polymeric pigment formation to form what is known as pyranoanthocyanins.
The advantage of polymeric pigment formation is that these complexes are not susceptible to sulfur dioxide bleaching or changes in wine pH. They are the most stable form of wine color known to scientists.
However, polymeric pigment formation tends to occur slowly in wine. Increased extraction of anthocyanins and tannins during primary fermentation offers available substrates to encourage polymeric pigment formation. However, increased extraction does not necessarily guarantee increased polymeric pigment formation.
Many winemakers add exogenous tannins at the beginning of primary fermentation in an effort to increase availability of tannins (or flavonoid substrates) when the anthocyanin concentration is highest. [Recall, anthocyanin concentration will decrease 10-20% by the end of primary fermentation.] This action is often referred to as the addition of “sacrificial tannins.”
However, not all exogenous tannins are created equally, or chemically react the same way in all wines. Additionally, many exogenous tannin products are not in a pure state (Mansfield 2015). Dr. Anna Katharine Mansfield recently reviewed phenolic wine chemistry and this concept in a 2015 Wines and Vine’s article titled: A Few Truths About Phenolics. For a more comprehensive understanding of phenolic chemistry, tannin structure (hydrolysed versus condensed tannins), and color stability, this article offers an easy read for any winemaker.
For winemakers looking to improve the color stability of hybrid varieties, remember that Springer and Sacks (2014) recently determined the high tannin-binding nature of many red hybrid varieties. This may indicate that tannin additions to red hybrid wines may not be useful.
Furthermore, lower anthocyanin concentrations (<200-300 mg/L catechin equivalents) may not be enough to drive the polymeric pigment reaction forward (i.e. create more polymeric pigments). A recent study by Sheridan and Elias (2015) investigate the polymeric pigment potential when acetaldehyde concentrations were increased during primary fermentation.
In order for polymeric pigment formation to occur, all three substrates are required at optimal concentrations (not clearly defined) of anthocyanins, other flavonoid units/tannins, and potentially acetaldehyde. This point alone may be a valuable indication for industry members to retain analytical records that measure the phenolic chemistry of incoming fruit and wines that have recently finished primary fermentation (prior to malolactic fermentation). Such records can act as indicators in terms of what further production methods may not be beneficial for red wine color enhancement. For example, a wine that is deficient in anthocyanin content (<200 mg/L) may not be a wine suitable for things like micro-oxygenation techniques that may contribute to polymeric pigment formation, but may benefit from potential co-fermentations with white varieties to enhance copigmented complexes.
In a future blog posts, we will explore the acetaldehyde-driven polymeric pigment reaction and how it influences red wine color stability. Additionally, this will be supplemented with a research-based literature review of common winemaking practices (e.g. cold soak, extended maceration, delayed MLF, etc.) that are commonly believed to enhance red wine color stability.
Boulton, R. 2001. The copigmentation of anthocyanins and its role in the color of red wine: A critical review. Am. J. Enol. Vitic. 52(2): 67-87.
Kennedy, J.A., C. Saucier, and Y. Glories. 2006. Grape and wine phenolics: history and perspective. Am. J. Enol. Vitic. 57(3): 239-248.
Mansfield. A.K. January 2015. A few truths about phenolics. Wines & Vines.
Ribéreau-Gayon, P. 1959. Recherches sur les anthocyannes de vegetaux. Application au genre Vitis. Librairie general de l’enseignement, Pairs.
Sheridan, M.K. and R.J. Elias. 2015. Exogenous acetaldehyde as a tool for modulating wine color and astringency during fermentation. Food Chem. 177:17-22.
Springer, L.F. and G.L. Sacks. 2014. Protein-precipitable tannin in wines from Vitis vinifera and interspecific hybrid grapes (Vitis spp.): Differences in concentration, extractability, and cell wall binding. J. Agric. Food Chem. 62(30):7515-7523.
Somers, T.C., and M.E. Evans. 1974. Wine quality: Correlations with colour density and anthocyanin equilibria in a group of young red wines. J. Sci. Fd. Agric. 25:1369-1379.
The Effects of Cluster Light Exposure, Timing of Leaf Removal, and Crop Load on Rotundone Development in Noiret Grapes and Wine
By: Laura Homich
What is Rotundone?
Rotundone is a hydrophobic sesquiterpenoid ketone found in the grape skin [1, 2]. In 2008, this compound was identified as the aroma compound which imparts the desirable spicy black pepper notes associated with Australian Shiraz [3, 4]. Rotundone has been identified in red varieties Schioppettino, Mourvèdre, Durif, and Vespolina as well as the white variety Grüner Veltliner . Additionally, rotundone was observed in several herbs and spices (nut grass, marjoram, rosemary, saltbush, geranium, thyme, basil, and oregano) and was found at the highest levels in white and black pepper .
Rotundone Sensory Characteristics
Most varietal aromas are created by a combination of several different chemical components. In contrast, rotundone is one of the few known aroma impact compounds, having the ability to impart a characteristic aroma with a single compound . The potency of this odorant results in a sensory detection threshold of 8 ng/L in water and 16 ng/L in red wine . Interestingly, sensory studies have shown that 20% of consumers were not able to detect this compound at 4000 ng/L (250 times the detection threshold), suggesting that two consumers drinking the same wine may have drastically different sensory experiences .
Goals of the Study
Several Pennsylvania growers have expressed interest in learning more about pepper aroma variation through viticulture practices as well as consumer preferences. Previous studies have found that higher rotundone concentrations are found in cool climate regions ; therefore, this characteristic pepper aroma is prevalent in some Pennsylvania grown varieties, notably Noiret. This work is first set out to determine the presence of rotundone in the Noiret variety. The effects of the timing of leaf removal (berries pea-sized versus post-veraison), cluster light availability, and crop load will also be investigated. Sensory analysis will be carried out to determine consumer sensory preferences of wine made from the leaf removal and sun exposure treatments.
A field trial has been established at the Cornell-NYSAES research station in Geneva, NY in collaboration with Dr. Justine Vanden Heuvel. Noiret berry samples were collected at four time points between pre-veraison and harvest. Canopy density was measured at three time points throughout the same period. Hail damage was observed on July 31st, resulting in injury on some of the exposed clusters. At harvest (October 28th), crop yield data was recorded for each treatment and berry samples were collected for Brix, pH, TA and rotundone analysis.
The Noiret grapes were crushed and destemmed according to treatment. Each treatment was split into two replicate fermentations, and each fermentation was chapitalized to reach a final Brix of 21. At the completion of primary fermentation, the wines were pressed and inoculated for malolactic fermentation. At that time, a strong black pepper aroma was noted in all treatments.
- Caputi, L.; Carlin, S.; Ghiglieno, I.; Stefanini, M.; Valenti, L.; Vrhovsek, U.; Mattivi, F. Relationship of changes in rotundone content during grape ripening and winemaking to manipulation of the ‘peppery’ character in wine. J. Agri. Food Chem. 2011, 59, 5565-5571.
- Mattivi, F.; Caputi, L.; Carlin, S.; Lanza, T.; Minozzi, M.; Nanni, D.; Valenti, L.; Vrhovsek, U. Effective analysis of rotundone at below-threshold levels in red and white wines using solid-phase microextraction gas chromatography/tandem mass spectrometry. Rapid Commun. Mass spectrom. 2011, 25, 483-488.
- Wood, C.; Siebert, T.E.; Parker, M.; Capone, D.L.; Elsey, G.M.; Pollnitz, A.P.; Eggers, M.; Meier, M.; Vössing, T.; Widder, S.; Krammer, G.; Sefton, M.A.; Herderich, M.J. From wine to pepper: rotundone, an obscure sesquiterpene, is a potent spicy aroma compound. J. Agric. Food Chem. 2008. 56, 3738-3744.
- Siebert, T.E.; Wood, C.; Elsey, G.M.; Pollnitz, A.P. Determination of rotundone, the pepper aroma impact compound, in grapes and wine. J. Agric. Food Chem. 2008. 56, 3745-3748.
Special thanks go to Dr. Justine Vanden Heuvel, Steve Lerch, and the team at Cornell University for allowing us to use the NYSAES Noiret plot for this study as well as assisting in field measurements. Thank you to Don Smith, Denise Gardner, and members of the Centinari, Elias, and Gardner labs for assisting with data collection, harvest, and winemaking.
Laura Homich is a M.S. Candidate in Food Science under the direction of Dr. Ryan Elias and Dr. Michela Centinari.
By: Denise M. Gardner
What is NE-1020?
Since the start of my tenure at Penn State Extension, we have been routinely highlighting the data and research affiliated with the NE-1020 project. Many have asked what NE-1020 is, and others have asked “Why are you participating in this trial? What is the point?” All valid questions!
As we come to an end of another vintage season, I thought it would be an interesting experience to review the NE-1020 project and what it is contributing to PA industry members.
The NE-1020 variety trials are a multi-state collaborative project, initially co-funded by the previously existing Viticulture Consortium-East, that were designed to evaluate the viticultural characteristics and wine quality potential of several wine grape varieties, cultivars and clones. Variety selections at each vineyard plot were determined based on dormant and growing season climatic conditions and research standards (i.e. standard varieties such as Cabernet Sauvignon, that would be tested at each vineyard site to establish a baseline and commonality at each site for research findings). These standard varieties are commonly referred to as “core varieties.”
Penn State has 2 research vineyards: 1 in Biglerville, PA and 1 at North East, PA near Erie. Vineyards were designed in a randomized complete block (RCB) design, meaning that “panels” of 4 vines were established at random throughout the ~1 acre of vineyard land at each site. The primary purpose of the RCB design is to allow for statistical analysis and to remove any potential variability due to location in the vineyard. This design is often affiliated with the cost to manage the NE-1020 sites, as varying training systems for hybrids and vinifera are frequent within a single row of vines. Additional costs are often related to data collection for all 20 varieties planted at one site. “Core varieties” for the Biglerville site include Cabernet Sauvignon and Merlot while “core varieties” for the Erie site include Chambourcin and Vidal Blanc. These varieties are harvested and made into wine annually, regardless of vintage variation.
After 3-4 years of vineyard establishment, Penn State began harvesting wine grapes in 2011. What a year to begin harvest and data collection! (I can hear the small grunts of laughter as we recall the 2011 season.) This was also the first year that we began making wines for research purposes from these varieties. Thus, as of the 2014 harvest, this will be the 4th year that Penn State has brought the Pennsylvania industry research wines for evaluation.
As this is a co-funded project between a Specialty Crop Research Initiative grant led by Dr. Tony Wolf at Virginia Tech and the PA Wine Marketing and Research Board (WMRB), we have tried to find active ways to engage pertinence of this study to industry members.
For example, one of the varieties that we have been evaluating includes Albarino, a white variety that is limited in Pennsylvania, and industry members get an opportunity to taste this wine every year at the WMRB Symposium.
The following notes the top 5 benefits affiliated with the NE-1020 project since I became involved with the study in 2011:
- Growing grapes and making wines annually has put Penn State viticulture and enology Extension personnel and researchers in touch with real vintage struggles felt by industry members. Prior to the establishment of the NE-1020 vineyard plots, there was limited focus on viticulture and enology research that could apply to the entire state. [I should note, however, that Penn State has had active research programs in Entomology and Plant Pathology that were, and still are, quite pertinent to the wine grape community in Pennsylvania and the Mid-Atlantic region.] The 2011 season was a perfect example in which the Penn State community committed to the NE-1020 project felt the effects of harvest season tropical storm and hurricane. While both sites were affected in different ways, we too dealt with low yields, increased disease pressure, and altered protocols for harvesting and wine production. It gave many members within the Penn State community some active speaking points to assist industry members. Other examples that pertain to this point include a greater awareness of enological issues, such as red wine color stability or dealing with heavy incidence of disease. These issues that are often iterated by industry members are also dealt with here at Penn State, and have been highlighted through processing and fermenting the NE-1020 varieties. This has led to point #2.
- Evaluating winemaking options to determine their effects on wine quality. Penn State Extension is actively listening to industry suggestions and applying enological questions they may have to our NE-1020 varietal study. In 2012, we began a series of yeast trials, which were tasted amongst industry members at the annual PA WMRB Symposium, based on suggestions made by industry members while I toured the state in 2011. Some of these yeast trials captured the interest of industry members, and a few people have altered some of their purchases based on the trials’ initial results. Additionally, red wine color stability was an issue that was brought to my attention through several regional visits in 2013. Therefore, we were able to design a few studies, with support from Lallemand and Enartis Vinquiry, to evaluate potential treatments that we have applied throughout the 2014 vintage year. These treatments are actively taking place, being evaluated and will be presented at the annual PA WMRB Symposium in 2015.
- The NE-1020 project allows us to record and evaluate micro-climates within Pennsylvania. One of the primary advantages of having 2 vineyard sites is being able to evaluate cultivar potential throughout regional differences within the state. This is actually one of the leading projects that I see as contributing to the definition of Pennsylvania’s regions and micro-climates. Tastings of those varieties that are planted at both Erie and Biglerville has led to a series of great industry discussions, questions, and future research trials. If you are interested in tasting some of these wines, please join us during the 2015 PA WMRB Symposium (in April at University Park, PA).
- The project initiated annual research winemaking and wine tasting at Penn State. At the 2012 PA WMRB Symposium, many industry members indicated that they had never tasted research wines before that day. I think this is a very valuable quality affiliated with the NE-1020 project. It has given Penn State the ability to produce research wines on an annual basis and develop a winemaking infrastructure. Research wines are never fully finished; the priority is to focus on varietal character in addition to physiological ripeness parameters (i.e. sugar and acid) during harvest and throughout production. Production for whites usually ends post-primary fermentation with a few rackings to get wines off of the lees. For reds, most wines are put through MLF before being placed in cold storage. Neither type of wine sees any oak treatment, fining, or filtration. This is done purposefully, with the intention that when industry members taste the wines, they can evaluate the particular treatment (whether it be vineyard or processing induced) and determine the wine’s potential (i.e. would it be good as is with little refinement, or should it go forward into an aging or oaking regime?). This concept of research winemaking and wine tasting is applied to many well-developed wine regions throughout the world and has helped progress the quality of wines in those particular regions.
- The NE-1020 project has allowed undergraduate students the opportunity to get real experience in viticulture and enology. I see Pennsylvania’s wine industry at the forefront of making great strides of progress in terms of wine quality. Much of this, I believe, starts with wine education. The NE-1020 project has provided a network that now involves undergraduate students to actively learn about wine, winemaking, grape harvesting, production methodology, wine sanitation, wine styles, and analysis. These experiences have led to a plethora of opportunities for our undergraduate students including internships or co-ops at wineries within and outside of Pennsylvania, wine research opportunities at large wine companies, and extracurricular learning for wine certifications. 2014 is the first year in which I see the investment in our student population directly benefiting the wine industry. Several students are now graduating, exploring “harvest hop” opportunities in other countries, and bringing their education and experience back to the Pennsylvania industry. A few students have been hired at Pennsylvania wineries for full-time positions, and aim to help improve the quality of PA-produced wines consistently. This is a direction that I hope to see advance and progress Pennsylvania as time moves forward, and it with great appreciation that I thank the wineries that have actively taught or hired students to progress their winemaking careers.
“This material is based upon funding provided by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under agreement No. 2010-51181-21599”
Introduction by Denise Gardner
I have ask a few students or recent graduates to contribute a few blog posts on their enology and viticulture experiences at Penn State, and how those experiences have influenced their career decisions. Over the past few years, I have had the pleasure to work closely with undergraduates on various tasks: the NE-1020 variety trial, lectures in classes, student research projects, and much more. These opportunities provide wine/grape-related experiences to students, and some become interested enough to pursue the field(s) as a career.
This first entry, written by Penn State senior, Brianne Morgan, describes her introduction to winemaking and how it became a career endeavor for her. I can still remember the first day I met Brianne, and I couldn’t help but smile when she told me that winemaking was “what she wanted to do with the rest of her life.” She obviously caught the bug! As you will see from her entry below, Brianne is an incredibly driven student, and it has led her to several industry experiences that have helped shape her into a valuable, educated winemaker that will continue to work in the Pennsylvania wine industry after her graduation.
By: Brianne Morgan
My name is Brianne Morgan and I am a senior majoring in Food Science. I have a love and passion for wine, especially the winemaking process.
I started my winemaking career with an eye-opening lecture and lab session, led by Denise Gardner, in my sophomore Introduction to Food Science class. She spoke about wine closures and we bottled elderberry wine using a manual corker. I was hooked. Immediately after Denise’s lecture, I went to see her and have been an undergraduate research assistant ever since. For me to find such an amazing mentor like Denise has made my experience in the industry that much better. At that point, I started learning as much as I could about enology and viticulture. While most people in wine industry may depict my first encounter with winemaking as the most boring part of wine production, for me it was an exciting adventure that I was ready to embrace.
My winemaking passion led me to an opportunity to work for three amazing companies during my undergraduate career as a student intern. My first experience was a six-month co-op for Mazza Vineyards in North East, PA.. This was my first harvest experience and it was a real world wind. Looking back, I can see why it is so important to work during a harvest before deciding you want to devote your life to the wine industry! I went from an inexperienced student to a “cellar rat” within a few months. However, I really enjoyed my “growing” experience in Erie because I learned all the foundational basics I am utilizing throughout my entire career as a winemaker. Going into this experience I was very concerned that I would not be able to endure the grueling hard work associated with harvest. However, as the weeks of that first harvest went by, the work became less daunting, and winemaking turned into a life-long career decision.
After spending six months at Mazza Vineyards, I realized I needed to learn more about viticulture to enhance my understanding about where wine originates: the grapes. This led me to my second internship during the summer after my junior year, which was at Penn State’s Lake Erie Regional Grape Research Station. I had the opportunity to work for Bryan Hed and Jody Timer, who taught me a lot about viticulture (the science of growing grapes) and entomology (the science of insects). It was awe-inspiring to see how the Penn State research team and Pennsylvania wine industry worked together to enhance viticulture knowledge within the state.
I also learned quite a bit about “vineyard work” and why it so important in the winemaking process: quality starts in the vineyard, but it extends into the winery. After spending the summer in the vineyard and heading back to Penn State in the fall to continue my undergraduate education, I was itching to do another harvest. With only a year-and- a-half of school to finish I decided to finish school first before completing another harvest. This was very hard decision to make because I have come to love the challenge of each harvest, but I knew I would have more opportunities to experience this in the coming years following graduation. By May, I was eager for another winery experience, and I decided I wanted to try to combine all that I had learned along the way in my next experience. This led me to Franklin Hill Vineyards in Bangor, PA where I had the opportunity to work within a winery created and led by women. . Elaine and Bonnie provided such an amazing work atmosphere for me, and I was able to promote my talents, which gave me the confidence in recognizing many skills I have learned. I had a grand scheme of work experiences at Franklin Hill including vineyard, cellar, and retail work, which, to be honest, I was quite nervous about. It is quite a challenge to wear so many hats within the winery. However, working in retail allowed me to connect with costumers and understand what they see in wine. As a winemaker, it is easy to sometimes forget consumer expectations while the work is confined to the cellar. Working with Bonnie in the cellar was a true learning experience that I will cherish and never forget.
I am confident that all of my internships and research experiences have led me to this point in my life in which I recognize that I would not be the person I am today without all of the people I have had the pleasure of working with throughout my college experiences. For that, I am truly grateful.
As a graduating senior I often get asked the question: “What will you be doing after graduation?” After having the privilege of spending some time in the wine industry, I really enjoy everything it has to offer and would like to contribute my knowledge to the Pennsylvania wine industry. With that being said, after receiving my degree I will be continuing my love for wine, and have accepted an Assistant Winemaker position at Franklin Hill Vineyards. Additionally, as I recognize the importance of gaining winemaking insight from outside of the Pennsylvania region, I am working to do a “harvest hop” to the southern hemisphere in the winter months of 2015. I am hoping that this experience will enhance my understanding of winemaking even further, and know that I can bring back what I learn to apply to my position held in Pennsylvania. I am excited to begin this new chapter of my life, and cannot wait to continue with the growing Pennsylvania wine industry.