By: Jody Timer, Research Technologist
The brown marmorated stink bug (BMSB), Halyomorpha halys (Stal) is an invasive species that has become a major pest in the eastern United States. This pest originally became a sizable problem in Mid-Atlantic vineyards, including southwestern Pennsylvania, during the 2010 growing season and continues to be a large-scale problem. The Lake Erie grape belt is the largest Concord grape growing region in the world. The recent appearance of the brown marmorated stink bug in Lake Erie vineyards has the potential to become problematic. After the mild winter of 2015-2016, the numbers of BMSB in this area began to increase rapidly. This winter, frequent complaints have been received from homeowner concerning the presence of BMSB in their houses.
BMSB have been found in both grape foliage and grape clusters; they seek the moisture, sugar, and warmth on the inside the clusters (especially overnight) and they often migrate to the cluster’s interior close to harvest. This makes the possibility of BMSB inside the cluster very likely when these grapes are mechanically harvested and transported to the processor.
All BMSB life stages (5 instars) have been observed in vineyards indicating that grapes are a suitable crop for BMSB development, and all stages have been found to cause direct damage to grapes (Bernon 2004). At the Lake Erie Grape Laboratory, we have maintained an adult BMSB colony on a diet of Concord grapes with no apparent development problems. It has also been estimated that the presence of 5 BMSB per grape cluster may lead to 37% loss in grape yield as a result of BMSB damage (Smith et al. 2014). With the yearly increase of numbers of BMSB in the Pennsylvania vineyards, the possibility of BMSB tainting the juice produced in this area is becoming a primary concern to processors, growers, marketers, and consumers.
Insects produce small, volatile molecules that may be imparted to juice and wine during crush. Humans are able to detect these molecules at extremely low concentrations. For example, 2-isopropyl-3-methoxypyrazine (IPMP) from Multicolored ladybeetles (ladybug taint) is detectable at 0.30 ng/L concentrations in Concord grape juice (Pickering et al. 2008). BMSB have a distinctive odor which has been described as green, cilantro-like, which may or may not be off-putting within grape juice aroma. BMSBs produce taint associated compounds as allomones, alarm pheromones, aggregation pheromones, and kairomones. These compounds are mainly released from the dorsal abdominal glands in nymphs and paired metathoracic glands in adults (Baldwin et al. 2014). When BMSBs are crushed along with grape clusters, release of these compounds could potentially taint in the juice.
Multidimensional gas chromatography mass spectrometry (MDGC-MS) analysis of stressed BMSB, adults and nymphs, has been used to identify more than 39 compounds. The volatile compounds in the taint are tridecane, dodecane, trans-2-decenal and trans-2-undecen-1-ol. Tridecane and trans-2-decenal together constitute at least 70% of BMSB taint (Baldwin et al. 2014; Solomon 2013). Trans-2-decenal, is the major irritant and is believed to be responsible for the potent stink odor from BMSB. However, being an extremely unstable compound it can easily break down, and its degradation products lack the distinctive BMSB odor (Baldwin et al. 2014). When trans-2-decenal was added to red wine (Pinot Noir) the morning of testing, the detection threshold was in the low microgram per liter (ug/L) range (Mohekar et al 2015). However, because trans-2-decenal is unstable, this may not reflect what happens when juice is processed and stored. Joe Fiola from University of Maryland, reported that while 5-10 BMSB per 25 pound lug of white grapes imparted a perceptible taint in raw juice for up to four months in some cases, the taint was not perceptible in the wine after fermentation (Fiola 2011). Mohekar and colleagues, from Oregon State, reported that trans-2-decenal, has a detection threshold in the ug/L range in Pinot Noir wines, and was able to be detected by tasters (Mohekar et al 2016).
Informal sensory testing with the on-site staff was performed at the Lake Erie Regional Grape Research laboratory. Small batches of grape juice were produced using a residential Kitchen Aid® juicer, and increasing numbers of BMSB were added. Batches of juice containing the equivalent of 0, 2, 10, and 25 BMSB per lug (~35 lbs. of Concord grapes) were tasted raw and after high-temperature, short-time pasteurization (HTST) by five staff members. In blinded triangle tests (2 blanks and 1 spiked sample), 5 of 5 individuals correctly identify the spiked sample of the 25 BMSB/lug juice (both raw and pasteurized); for the 10 BMSB sample, 4 of 5 correctly identified the spike in raw juice, and 5 of 5 identified the spiked sample for the pasteurized juice. The following month the pasteurized juice was re-tasted by 10 individuals and similar results were obtained. These tests suggest 25 BMSB/lug are sufficient to induce a perceivable flavor change in Concord grape juice. Following this testing, a set of samples were processed at the Food Science laboratory of Penn State, using industrially relevant methods (equivalent to Welch’s Corporation processing techniques), to assess if the odor-causing compounds secreted by BMSB were stable enough to transfer through the juicing, processing, pasteurization, and storing of grape juice and therefore cause it to be rejected by consumers. Large scale sensory tests were then run with regular grape juice consumers to quantify rejection thresholds for BMSB-spiked, processed grape juice.
Grape clusters, with varying amounts of BMSB (0, 4, 8, 16, 24, and 32 BMSB, per 35 lbs), were crushed and destemmed; the juice was pasteurized, clarified and blended. Following storage for 8 weeks (2 months after initial processing), sensory testing was performed with grape juice consumers in the controlled sensory testing facility to determine rejection thresholds for different levels of BMSB. Sensory testing was then repeated 8 weeks later (4 months after initial processing).
Despite the use of BMSB levels that clearly caused a noticeable change in the flavor of processed juice in pilot testing, we were unable to find a level of BMSB that caused rejection in consumers following processing and storage at either time point.
As the area’s BMSB population increases, this research will be notably important for processor to determine threshold levels at harvest. This research suggest that taint from BMSB at high but realistic doses for the Lake Erie grape-growing region will not influence consumer acceptability. Conversely however, our results may not generalize to smaller producers in the area who make grape juice using exclusively from Concord grapes. Typically, this juice is sold as fresh juice with a limited shelf life. These smaller growers and producers should be aware of the possibility of taint in their juice especially with the increasing numbers of BMSB in the region. Pre-harvest scouting for BMSB should be conducted to determine if a pre-harvest BMSB insecticide spray should be applied.
Baldwin, R.L. IV, A. Zhang, S.W. Fultz, S. Abubeker, C. Harris, E.E. Connor, and D.L. Van Hekken (2014) Hot topic: Brown marmorated stink bug odor compounds do not transfer into milk by feeding bug-contaminated corn silage to lactating dairy cattle. J. Dairy Sci. 97. 1877-1884.
Bernon, G. (2004) Biology of Halyomorpha halys, the brown marmorated stink bug (BMSB) Final Report—USDA APHIS CPHST Project T3P01. USDA APHIS.
Fiola, J.A. (2011) Brown Marmorated Stink Bug (BMSB) Part 3-Fruit Damage and Juice/Wine Taint. Timely Viticulture. University of Maryland extension,
http://www.grapesand fruit.umd.edu. Accessed October, 2016
Mohekar. P. (2016) Brown Marmorated Stink Bug (BMSB), Halyomorpha halys Taint in Wine: Impact on Wine Sensory, Effect of Wine-processing and Management Techniques. Dissertation Oregon State University
Mohekar, P., Tomasino, E., Wiman, N.G., (2015) Defining defensive secretions of brown marmorated stink bug, Halyomorpha halys. Presented at the 2015 Annual Meeting of the Entomological Society of America, Minneapolis, MN
Pfeiffer, D. G., T. C. Leskey and H. J. Burrack, (2012) Threatening the harvest: The threat from three invasive insects in late season vineyards, pp. 449-474. In N. J. Bostanian,
Pfeiffer, D., J. Fiola, B. Lamp, K. Rane, A. Nielsen, D. Polk, B. Petty, D. Ward, M. Saunders, J. Timer, C. Hedstrom, P. Mohekar, N. Wiman, E. Tomasino and V. Walton, (2013) BMSB in Vineyards and Wines. www.stopbmsb.org/stopBMSB/assets/File/Research/BMSB…/Vineyards-Vaughn.pd . Accessed September 2016
Pickering, G.J., Karthik, A., Inglis, D., Sears, M. and K. Ker, (2008). Detection Thresholds for 2-Isopropyl-3-Methoxypyrazine in Concord and Niagara Grape Juice. Journal of Food Science, 73 (6): S262-S266.
Prescott, J., Hayes, J. E., & Byrnes, N. K. (2014). Sensory Science. In N. K. V. Alfen (Ed.), Encyclopedia of Agriculture and Food Systems (pp. 80-101). San Diego: Elsevier.
Smith, J.R., Hesler, S.P., and Loeb, G.M., (2014) Potential Impact of Halyomorpha halys (Hemiptera: Pentatomidae) on Grape Production in the Finger Lakes Region of New York. J. Entomol. Sci. 49, 290–303. doi:10.18474/0749-8004-49.3.290
Solomon, D., D. Dutcher, and T. Raymond, (2013) Characterization of Halyomorpha halys (brown marmorated stink bug) biogenic volatile organic compound emissions and their role in secondary organic aerosol formation. J. Air Waste Manag. Assoc. 1995 63, 1264–1269.
Welch’s Corporation, www.Welch’s.com Accessed August 2016.
By: Denise M. Gardner
Wine blending is often highlighted as the artistic portion of wine production. However, blending can also be used for practical or economical purposes. This blog post will explore some of the common introductory reasons for using wine blending to craft red wines.
Why do winemakers blend wines?
Wine blending is a wine production technique that can be used for a multitude of purposes in order to finish a wine. Some of these reasons include, but are not limited to:
- Creating a house style
- Improving vintage consistency
- Highlighting vineyard terroir
- Enhancing a wine’s positive sensory characteristics
- Minimizing a wine’s undesirable sensory components
- Balancing oak flavors
- Altering a wine’s chemistry
- Managing wine inventory
- Blending out (i.e., getting rid) of problem wines
- Additional reasons…
House style and vintage consistency can be very important for a brand’s marketability and reliability amongst consumers.
Many Champagne producers rely on blending to create a house style cuvee associated with their sparkling wines. While these are not red wines, creating a house style is often based on specific sensory or taste characteristics that are desirable by the winemaker and contribute to major blending decisions. These blending decisions help minimize vintage-to-vintage variation and variation in grower supplies of fruit while enhancing consistency for their brand.
The same concept can be applied to red wines, but with the use of red wine grape varieties. House blends can be represented with blending names such as “Proprietor’s Red” or “Winery’s Name House Blend.” Having wines that are labeled as a blend provides flexibility for the winemaker to create a wine that is of a similar style on a year-to-year basis while altering the wine grape varieties that go into the blend every year. Below are some popular examples of red wine blends that emphasize this point in creating a house style red blend wine.
The other advantage of creating house blends is that these wines allow winemakers to work with variations in varietal inventory. If we take the last example above, Cupcake Vineyard’s Red Velvet wine, while three different varieties make up the blend, the percentages of each variety contributing to the blend can vary from year-to-year. This may help mediate changes in yield each harvest season.
Improving Annual Wine Consistency or Highlighting Vintage Variation
Blending can a winemaker’s best tool in enhancing vintage consistency, especially in cooler growing regions where vintage-to-vintage variation is prevalent. There are a couple of ways that winemakers have been able to accomplish this practice.
- Reserving previous vintage wines for blending into future vintages.
- Purchasing bulk grapes/juice/wine from warmer climatic regions and blending in small amounts to each vintage.
While neither of these practices may be ideal for terroir expression of certain wine blends, these blending practices provide opportunities to expand a winery’s product portfolio and enhance wine style variation associated with the brand.
In contrast, blending can be used as a tool to illustrate and celebrate vintage variation, which is an inherent component of winemaking. Not only do these wines offer unique educational and marketing opportunities, this is a tactic that can be used to differentiate premium products within a brand and cater to those consumers that are wine enthusiasts or have a greater interest in vintage-to-vintage variations for a particular brand. This practice can also better capture the brand’s terroir, which can be a key marketing feature for wineries with estate vineyards. Additionally, these wines offer exceptional tasting experiences for consumers that enjoy vertical tastings of multiple vintage years, and can be used for various sale promotions over several years.
A common example of this practice is demonstrated by Allegro Winery & Vineyards in Brogue, PA. The Cadenza and Bridge wines are designed as premium brands, vintage dated, and blended to a particular style in those years that produce the best quality red wine blends.
Wine blending to fix problem wines
While less artistic and perhaps a bit less creative, blending can also be used to help minimize the impact of problem wines or wines that have noticeable defects, flaws or quality shortcomings. Minor problems can often be partially masked by being blended into aromatically rich varieties like Concord, Niagara, or Catawba. Noiret, a red hybrid variety, also has a relatively rich aroma/flavor of black pepper which may be an alternative aromatically rich blending variety, as well as the utilization of formula wines with strong added flavors.
Wines suffering from minor oxidation problems can often be added to richer, fresher, younger wines at minimal levels without hindering the fresher or younger red wine. Additionally, wines with a slightly elevated VA (~0.50 – 0.70 g/L acetic acid) can be added to wines with a lower VA (<0.40 g/L) after the high VA wines have been properly treated and stabilized to avoid contaminating a clean wine.
The key thing to remember when blending clean-wines with problem-wines is that winemakers want to avoid creating a series of lower quality wines in order to get rid of a problem wine. Keep in mind that it is not likely that one will be able to create a “unique blend” by using problem wines to any degree. Winemakers are more likely to create a “good enough” or “commercially acceptable” wine when utilizing blending for this purpose.
All wines that have issues should be analytically and sensorially evaluated before and after blending to ensure chemical and microbiological stability.
By: Denise M. Gardner
The Pennsylvania Wine Marketing and Research Board (PA WMRB) annually awards researchers and graduate students grants to explore pertinent topics to the Pennsylvania wine industry. For the 2016 – 2017 fiscal year, four projects were awarded industry-funded grants. Results from these four projects will be presented at the 2017 Symposium, co-hosted by the PA WMRB, Penn State Extension, and the Pennsylvania Winery Association (PWA).
Registration is being organized through the PWA, and can be found here:
This year’s Symposium, held on Wednesday, March 29th at the Nittany Lion Inn (University Park, PA) will only run in the morning and is packed with 5 sessions of information pertinent to both the enology and viticulture fields in Pennsylvania. At the close of the Symposium a lunch will be provided for all attendees.
Guest Speaker has Enology and Tannin Focus
The WMRB Symposium key guest speaker is Dr. Catherine Peyrot des Gachons, Winemaker Consultant at Chouette Collective. Dr. Peyrot des Gachons has assisted Pennsylvania wineries with enhancing their quality production for several years. She will be speaking towards her tannin and wine aroma matrix research that she has been working on at the Viticulture and Enology Department through the University of Montpellier (France).
Tannins: Modulation of wine structure and aroma
From environmental factors on tannin biosynthesis to human interventions to modulate tannin content in wine what do we know and what can we do to modulate wine structure. Can this tannin content impact wine aroma? The presentation will focus on few main points of interest with practical applications.
An additional enology-based presentation will feature Laurel Vernarelli, a graduate student in Dr. Ryan Elias’s lab within the Penn State Department of Food Science. Laurel’s presentation will be an extension from Dr. Gal Kreitman’s work that was presented last year on predicting reductive off-odors in wines. Laurel will explore the use of copper fining in wine production and the potential impact it may have on wine quality. Given the prevalence of reductive off-odors, including hydrogen sulfide, and heavy reliance on copper fining, this topic should be of considerable interest to most wineries.
Reconsidering copper fining in wine
This presentation will include a brief overview of copper fining, along with the impact of reductive thiols and recent findings describing the effect that copper has in wine. A method for using immobilized copper materials in place of copper fining is described. Depending on the result obtained, winemakers can make informed decisions for use of alternative fining techniques when dealing with reductive issues.
For those with an interest in viticulture, this year’s program promises to deliver some key updates. Bryan Hed, Research Technologist for the Department of Plant Pathology, will present his annual updates regarding disease management for Pennsylvania vineyards. For those that are frequent blog followers, Bryan is a lead contributor to the important seasonal reviews. These tend to be very popular posts for growers and his presentations are always informative and practical. If you missed the 2016 seasonal reviews, you can find them here:
- Looking back at the 2016 season
- Late summer/early fall disease control, 2016
- 2016 Post-bloom disease management review
- 2016 Pre-bloom disease management review
Bryan’s talk at this year’s Symposium is a continued study with results collected over 2 years, which helps initiate trends and suggestions useful towards growers.
Updates on Grape Disease Management Research
Fruit zone leaf removal can be a very beneficial practice in the management of harvest season bunch rot. Bryan will start his presentation by briefly reviewing the pros and cons of different timings of this practice. In addition, leaf removal by hand is very expensive and labor intensive, and with the increasing scarcity and rising cost of hand labor, mechanization is crucial to increasing cost effectiveness and adoption of this practice, no matter what the timing. Bryan will follow up with an in depth discussion of the progress made toward mechanizing an early, pre-bloom leaf removal and comparing its effectiveness over a variety of wine grape cultivars and training systems during the past two seasons.
Maria Smith, Ph.D. candidate in Dr. Michela Centinari’s lab, will discuss her research regarding early leaf removal in Gruner Veltliner vines. Maria and Dr. Centinari have previously written a blog post pertaining to leaf removal strategies for Mid-Atlantic vineyards, which could act as an excellent primer to Maria’s presentation in March. Her presentation will deliver two-years (2015, 2016) of data regarding the effects of early leaf removal and cluster thinning techniques on Gruner Veltliner vines.
Vine response and management costs of early leaf removal for yield regulation in V. vinifera L. Gruner Veltliner
Early leaf removal (ELR) and cluster thinning (CT) were applied and compared for yield regulation in Grüner Veltliner over the 2015 and 2016 growing seasons. Early leaf removal was performed at two different times, trace-bloom and fruit-set. We compared the effects of ELR and CT on grape quality, vine health, and economic costs to un-thinned vines.
Finally, Dr. Michela Centinari will follow up with further results regarding sprayable products to reduce frost damage in wine grape vineyards. Michela’s frost research has been a prominent topic at previous Symposiums, and is often featured here on the blog site. While the updated results that will be presented at the 2017 Symposium have not yet been reported through Penn State Extension, please see some of her past blog posts pertaining to frost control and freeze damage in the vineyard:
- Understanding and Preventing Spring Frost/Freeze Damage – Spring 2016 Updates | Wine & Grapes U.
- Updates on Freeze Injury in Grapevines
- Evaluate cost-effective methods to decrease crop losses due to frost injury
- An update to studies on frost injury, by Maria Smith
Spray-on materials: can they reduce frost damage to grapevines?
Dr. Centinari will present results of studies conducted to test the efficacy of sprayable products as a low-cost frost protection strategy. Two materials Potassium-Dextrose-Lac (KDL) and a seaweed extract of Ascophyllum nodosum, were tested for their cryo-protective activity using a controlled-freezing technique on several grapevine cultivars.
We hope to see you there!
By: Andrew Harner and Michela Centinari
As we move forward through the winter season, many growers have begun or are planning on beginning their annual dormant pruning within the coming weeks. Though a routine task within the vineyard, dormant pruning is essential to maintaining a balanced vineyard that produces quality fruit. With that in mind, this post will both review the basics of dormant pruning and present a series of important considerations to keep in mind when pruning and planning to prune.
With that being said, we will begin with the basics: What is dormant pruning?
In short, dormant pruning is the intentional removal of grapevine tissue, in the form of canes, cordons, trunks, etc., during the annual period of plant dormancy.
What are we trying to gain or change through dormant pruning?
In order to understand the rationale and goals behind dormant pruning, it is first important to understand the biology of grapevines and their physical characteristics that have evolved over thousands of years. Grapevines behave as lianas, or woody, lignified vines that lack a specific growth form on their own; instead, they use other means of support for their growth (i.e., trees or trellis wires). Moreover, grapevine shoots exhibit an indeterminate growth pattern and will continue to grow as long as growing conditions allow and are hospitable. This helps explain why the wild grapevine species endemic to North America tend to be sprawling masses of extensive shoots, and overall have a vigor that differentiates grapevines from many other fruit crops. As a whole, they will remain in this vegetative state until there is access to sufficient sunlight to induce floral development.
Both trellising and pruning are means of harnessing this inherent productivity, with the goal of transitioning it into reproductive growth and consistent, quality fruit yields. Dormant pruning is the primary tool used by grape growers to maintain vine shape, as defined by the training system, and to effectively regulate crop load (fruit mass/vine size) so that a vine’s bearing capacity matches its vegetative vigor capacity. This balance is especially important, as over- or underestimating a vine’s capacity to ripen a fruit crop may result in overly vigorous or overly cropped vines, both of which can have long- and short-term negative consequences. Additional crop load adjustments through shoot thinning and cluster thinning may also be necessary during the growing season to fine-tune grapevine crop load.
Principles of vine balance and essential considerations
Various efforts by researchers to quantify the effects of pruning on vine performance have resulted in the establishment of a few metrics that can be used to guide dormant pruning. Perhaps one of the most basic but important ways to measure vine size is through the collection and weighing of the canes removed by pruning (Figure 1). These numbers could be used to compare final vegetative biomass between vines of any given season, and when combined with the crop yield measurement—taken on the same vines at the previous harvest—can be used to calculate the ratio of fruit yield to vegetative mass. This ratio is the basis for the Ravaz index (yield/pruning weight), an early metric of vine balance first pioneered by the French viticulturist Louis Ravaz during the early 20th century.
Otherwise called crop load, optimal Ravaz index values vary by grapevine species and variety: research on Vitis vinifera has suggested that optimal crop load values fall between 5 and 10; a Ravaz index below 5 indicates that vines were potentially under-cropped (a small vine with a large crop), while a Ravaz index close or above 10 indicates that vines may have been over-cropped (a small vine with a large crop). American and Canadian studies have suggested that interspecific hybrid varieties, more of which are grown in Pennsylvania and other regions of the northeast and Midwest US, are capable of achieving higher crop load values without compromising fruit quality.
Caution is still necessary when thinking about crop load, however, as these general ranges fail to detail variations in a vine’s capacity to ripen its crop due to genotype, weather, soil, and management strategies. Exceptions can occur, and often do occur. While any variety may produce high yields with good fruit quality at one site – and subsequently attain high Ravaz index values – the same variety may not be able to ripen the same amount of fruit at less vigorous sites and under different weather conditions (i.e., locations with shorter growing seasons and/or with lower heat accumulation).
The concept of balanced pruning focuses on cropping vines at yields that are tailored to the vine’s vigor potential and size. The goal is to prevent under- or overcropping and ensure proper shoot maturity and winter-hardiness through a conscious approach to pruning: for example, more vigorous vines are allocated a greater number of buds so the vegetative growth potential is spread across a greater number of nodes, resulting in lower individual shoot vigor. In terms of managing weaker vines, fewer buds are to be retained so the remaining buds will produce more vigorous shoots.
Simple model equations have also been developed for balanced pruning that allocate specific numbers of nodes based on total pruning weights. A classic example is the equation for Concord vines: 30+10, where 30 nodes are retained for the initial pound of pruning weight, and 10 nodes retained for every additional pound of pruning weight thereafter. This specific formula is unsuitable for hybrid and V. vinifera vines, however, as Concord vines are typically cropped at higher levels. Other suggested formulas are based on cluster size, with large clustered varieties (e.g., Chancellor) at 20+10, small clustered varieties (e.g., Marechal Foch) at 20+10, and medium clustered varieties at 10+10. Varieties with large clusters and highly fruitful shoots tend to overcrop, so additional cluster and shoot thinning may be necessary for optimal balance; this counteracts any overcropping that could potentially occur if the formula is followed strictly. Again, these formulas are not the rule, and exceptions to them can and will occur. Instead, it is immensely important to use them as a guideline and tailor final node counts to the individual vine or variety, while keeping in mind site and variety vigor, climate, soil type, and training system.
What differences exist between cane and spur pruning?
Depending on the type of training system implemented and the variety being pruned, dormant pruning methodology consists of either cane pruning or spur pruning. The difference lies in the length of bearing unit, or the one-year old wood, retained: spurs are typically 2-3 nodes long, whereas canes are longer – usually between 8 to 15 buds.
With spur pruning, the one-year old fruiting canes are pruned back to spurs of 2-3 nodes, being the fruiting wood that will yield new shoots in the subsequent growing season. This allows for the retention of cordons and mature, wooden arms (Figure 3).
Conversely, cane pruning entails the removal of one-year old growth back to the head or crown of the vine, with the retention of two canes – one for each side of the trunk – for the bilateral training systems that are used in many vineyards in the eastern US (Figure 4). In sites with high vigor potential, growers may choose to leave four canes instead of two (Figure 2A & B, and Figure 5), which will help to accommodate more vigor and leave the vine more balanced. Furthermore, choosing canes of the right size is especially important—the preferred cane diameter is within a range of 3/8 to 1/2 inch, easily represented by the diameter of a pencil—as thick, excessively vigorous bull canes are as unsuitable as thin, spindly canes. Canes that are too thin or too thick will only yield shoots and fruit of inconsistent quality, whereas well-matured canes with diameters within the mentioned range will only help with maintaining full canopies and fruit-bearing capacity.
Choosing the right pruning system is dependent upon many factors: the variety being grown is especially important, as basal buds of some varieties (e.g., Sauvignon blanc, Nebbiolo) have low fruitfulness and are therefore unsuitable for spur pruning. Vine spacing, mechanization, available labor, and time availability may also affect the choice of a pruning technique. Cane pruning requires more labor in the form of tying down canes, but cane-pruned vines generally require less shoot thinning during the growing season. It is therefore important to select canes with equally spaced internodes, as this allows for equally spaced shoots and reduced shoot crowding.
If the vines are spur-pruned, retaining equally spaced spurs is crucial in order to obtain uniform canopy density and improved sunlight penetration, though shoot thinning during the growing season will likely be necessary as well. Regardless of the pruning method chosen, maintaining sunlight into the renewal zone is essential, as poor light penetration will inhibit bud fruitfulness with negative consequences for future yield and fruit quality.
How do I know when to prune? Pruning strategies for cold climate viticulture
Regardless of the seemingly obvious answer that dormant pruning should be implemented during the dormant, winter season, the timing of pruning could have major implications for the following season’s growth.
In grape-growing regions where there is risk of exposure to damaging cold events, such as Pennsylvania, pruning during the late winter is preferred. Low winter temperature events can damage buds and vascular tissues of mainly cold-tender vine varieties – all vines have limits to their cold-hardiness, however, and even very cold-hardy hybrids can sustain injury to buds and other tissues under exceptionally cold events.
Pruning in the late winter would allow growers a chance to assess vine injury and accordingly adjust the number of buds/nodes to retain. Yet due to labor and time constraints, it is often not possible to do all pruning in the late winter; instead, it is best to begin with the most cold-hardy varieties and leave more cold-susceptible varieties until later in the season. Moreover, in an instance where a damaging cold event does occur, various levels of additional buds are recommended for retention during pruning, depending on the percentage of bud necrosis (Table 1). A high level of bud injury might require differing pruning strategies, such as retraining new trunks and renewing larger parts of the vine, but these topics will not addressed within this post.
When forming a plan for pruning, it is equally important to consider the topographic and microclimatic variability of a vineyard site, as this has implications for air drainage. Vines, rows, or blocks that are at lower elevations than the rest of the vineyard may be more susceptible to cold temperature injury if dense, cold air drains to these low points and pools there. This creates pockets of air that will have lower temperatures than the ambient temperatures of any surrounding blocks, rows, etc. that are at higher elevations.
This is also a consideration worth keeping in mind as the season progresses to bud-break, as these same microsites are also more susceptible to damaging spring frosts and could have any early season growth quickly curtailed. In these cases, double-pruning can be a potential strategy when spur-pruning: canes are first pruned back to long spurs/canes of 5-8 buds, which will allow for terminal bud growth first and will suppress basal bud growth due to apical dominance. Once the risk of frost has passed, a final pruning cut should be made to cut the spurs back to 2-bud spurs. An alternative for cane-pruned vines would entail leaving long canes and extra canes until the threat of frost has passed, and then subsequently making a final pruning cut that leaves the canes at the desired bud number.
Through this post we have hoped to provide an overview of balanced pruning methodology, as well as emphasize considerations that are essential to successful pruning and maintaining balanced, fruitful vines. We realize that many growers tend to have their own styles and methods of pruning, however, and their own rationale for using specific strategies that may differ from the ones listed here. We would be happy to hear about their systems, and any strategies that have proven successful for their vineyards and vines, or adaptations they have implemented to handle specific circumstances or issues within the vineyard. Please feel free to contact us with your ideas and experiences regarding dormant pruning.
In addition to a number of books and publications that detail balanced pruning methodology, principles, and philosophy, there exists an extensive online reservoir of material that can be easily accessed for guidance related to pruning. More detailed explanations and even experiment findings related to pruning can be found in the Wine Grape Production Guide for Eastern North America, The Grapevine: From the Science to the Practice of Growing Vines for Wine, Sunlight Into Wine, and myriad other texts.
Many cooperative extension services (Penn State University, Washington State University, Cornell University, etc.) can be particularly helpful with providing information about pruning, and instructional presentations and in-field videos can easily be found online through a simple web-based browser search or through the aforementioned universities’ cooperative extension websites.
Iland, P., P. Dry, and T. Proffitt. 2011. The grapevine: From the science to the practice of growing vines for wine. Patrick Iland Wine Promotions Pty Ltd, Adelaide, Australia.
Jordan, T.D., R.M. Pool, T.J. Zabadal, and J.P. Tomkins. 1966. Cultural practices for commercial vineyards. Miscellaneous Bulletin 111. Cornell University, Ithaca, NY.
Reynolds, A.G., and T.K. Wolf. 2008. Pruning and training. In Wine Grape Production Guide for Eastern North America. Tony K. Wolf (ed.), pp. 98-109. NRAES, Ithaca, NY.
Willwerth, D., K. Ker, and D. Inglis. 2014. Best management practices for reducing winter injury in grapevines. Cool Climate Oenology & Viticulture Institute, Brock University, Ontario, Canada.
Andrew Harner is a graduate student at Penn State, where he is pursuing a MS degree as a member of the Plant Science Department and studying how climatic and environmental factors influence rotundone synthesis and concentration in Noiret wine grapes with Dr. Michela Centinari. He is currently funded by the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA. Drew graduated from Cornell University in 2016, where he focused his studies on Horticulture and Viticulture/Enology and was first introduced to the world of grapevines and plant-based research. Following the conclusion of his MS program he hopes to continue onwards within academia and pursue a PhD, and spends much of his free time either reading, cooking, or outside exploring the natural areas and parks of the U.S.
By: Denise M. Gardner
In a previous post, we discussed ways in which nutrient management during primary fermentation can affect hydrogen sulfide formation and the overall “health” of the wine. This week, we’re going to explore how to mediate hydrogen sulfide aromas and flavors in a finished wine.
Sulfur-Containing Off Aromas
In general, many wine sensory scientists and wine experts will agree that is relatively a bad habit to use the term “sulfur” to describe off-odors associated with hydrogen sulfide or “stinky” aromas that are usually described by the term “reduced.” One of the main arguments for avoiding “sulfur” as a description term for an aroma is due to the fact that there are actually several forms of aromatic sulfur-containing compounds found in wine, and they can have very different aromas (smells, odors) associated with that one compound. The most common groups of aromatic sulfur-containing compounds in wine are:
- Sulfur dioxide (SO2)
- Hydrogen sulfide (H2S)
- Mercaptans or Thiols
Additionally, many sensory experts will advise further to avoid using the chemical names as descriptors for describing an aroma found in wine (e.g., using the term “hydrogen sulfide” to describe the hard-boiled or rotten egg aroma). It is typically recommended to use an actual descriptor when describing an aroma (e.g., using the term “rotten eggs” when that smell exists in wine).
Sulfur Dioxide (SO2)
Sulfur dioxide is an antioxidant and antimicrobial preservative frequently used in wine production. However, it is also produced by yeast during primary fermentation, which is why wines (and other fermented products) cannot be sulfur dioxide-free (commonly referred to as “sulfite free” in the mass media). The aromatic descriptor commonly associated with a high concentration of sulfur dioxide is termed “burned match,” but a high concentration of sulfur dioxide can also cause a nasal irritation that many will describe as nasal burning. For more information on sulfur dioxide and managing its concentration in wine, please refer to this Wine Made Easy Fact Sheet produced by Penn State Extension.
Hydrogen Sulfide (H2S)
Hydrogen sulfide is an aromatic compound that is commonly described as having a “rotten egg” or “hard-boiled egg” aroma. Like many sulfur-containing compounds, hydrogen sulfide has a low sensory threshold (<1 – 1 part per billion, ppb), indicating that about 50% of the population could sense this compound at that concentration without being able to identify it, specifically, as hydrogen sulfide.
As we saw in our previous post, hydrogen sulfide development can result as a component of poor nutrient management during primary fermentation. Residual elemental sulfur from pesticide sprays has also been linked to latent development of hydrogen sulfide in wines. In a 2016 edition of Appellation Cornell, Dr. Gavin Saks’ lab provided a detailed and practical report on how hydrogen sulfide can be a problem for winemakers post-bottling and the potential links to hydrogen sulfide development as a function of residual sulfur from the vineyard (Jastrzembski and Saks, 2016).
Occasionally, winemakers may also experience hydrogen sulfide formation during a sur lie aging period; a time in which the finished wine remains on the lees when lees are stirred in the wine. It is also common for sparkling wines, produced in the traditional method, to exhibit a small perception of hydrogen sulfide when the bottle is first opened.
Mercaptans/Thiols and Disulfides
Finally, mercaptans or thiols, sulfur-containing compounds that contain the functional group –SH, and disulfides, sulfur-containing compounds that contain a S-S bond, can also be problematic for winemakers when found at high concentrations.
The presence of sulfur-containing volatile compounds is not always considered detrimental to wine quality. For some wine grape varieties (e.g., Sauvignon Blanc), these classes of compounds can make up their varietal aroma. In very small concentrations, sulfur-containing compounds can also be aroma enhancers, indicating that their presence can actually make the wine smell fruitier than if they were not present in the wine. However, when at substantial concentrations, volatile sulfur-containing compounds can also produce various “stink” aromas that mask a wine’s fruitiness, freshness, and make the wine generally unappealing. This is phenomena is dependent on the concentration of the sulfur-containing compound and the chemical makeup of the solution (i.e., wine) it is in.
Mercaptans or thiols and disulfides have a variety of descriptors associated with them, and their perception is largely based on concentration. When we’re discussing the negatively-associated descriptors, common terms include: garlic, onion, canned asparagus, canned corn, cooked cabbage, putrefaction, burnt rubber, natural gas, and molasses amongst others.
Are There Sulfur-Containing Off-Aromas in Your Wine?
To identify if hydrogen sulfide, mercaptans/thiols, or disulfide-based off-odors exist in your wine, it may be best to use a copper screen as a bench trial. While analytical identification of these compounds is possible, it is often expensive and leaves the winemaker guessing on what to do next.
For a quick assessment of a wine’s aroma, winemakers can drop 1-2 pre-1985 copper pennies into a glass of wine to see if the aroma freshens. The freshening aroma is due to the fact that the copper from the penny is reacting with the sulfur-containing compounds in the wine and making them aromatically inactive.
A technical copper screen takes a bit more work and should be conducted in a quiet and aromatically-neutral environment. It is recommended to do this outside of the cellar.
Copper addition, in the form of copper sulfate, is often used to remediate aromas/flavors associated with hydrogen sulfide. One-percent and 10% copper sulfate solutions can be purchased through your local wine supplier. The basic protocol associated with a copper screen is as follows:
- Add 50 milliliters of wine to two glasses.
- Label one glass “control” and the other “copper addition” (see image below).
- Add 1 mL of 1% copper sulfate to the “copper addition” glass.
- Cap both glasses for 15 minutes. Sniff the aroma of each wine.
Sniff (smell only!) both glasses. Most people start with the “control” and smell the treated wine (wine containing copper sulfate) second. If the aroma/flavor of the “copper addition” glass has improved, or the hydrogen sulfide aroma has subsided, then a copper addition trial should follow to determine the exact concentration of hydrogen sulfide needed to clean up the wine in question. Remember that the legal limit for copper allowed in a finished wine is 0.5 ppm. For a full protocol on how to run a copper addition bench trial, please refer to this Penn State Extension Wine Made Easy Fact Sheet.
Treatment of Sulfur-Containing Compound Off-Aromas
Sulfur-containing compounds are quite reactive, which can make dealing with them fairly difficult. Many educators agree that the best way to treat sulfur-containing compounds, especially those that stink, is to prevent their existence as best as possible.
In the Appellation Cornell newsletter that focused on sulfur pesticide residues, Jastrzembski and Saks (2016) recommended that sulfur residue concentrations should not exceed 1 mg/kg at harvest in order to avoid latent hydrogen sulfide or sulfur-containing off-aromas later in processing and storage. Additionally, many experts recommend appropriately treating fermenting musts with nutrient management strategies based on the starting YAN concentration to minimize the incidence of hydrogen sulfide formation during primary fermentation. This topic was covered in a previous blog post.
As described above, winemakers may also opt to treat the wine with copper sulfate to try to reduce the perception of hydrogen sulfide or other sulfur-containing aromas. It should be noted that aromas caused by disulfides cannot be mediated with a copper sulfate addition.
There has been more conversation in the academic community regarding the reemergence of hydrogen sulfide or sulfur-containing off-aromas after a wine has been treated with copper and post-bottling. The theory around this appears to circulate around residual copper initiating reactions in the wine that lead to more sulfur-containing off-odors. This continues to be an ongoing discussion amongst researchers and will likely be a hot topic within with the wine industry. For now, it is important for winemakers to understand that there may be a risk of off-odors reemerging post-copper treatment and post-bottling. This topic will also be discussed to some degree at the 2017 PA Wine Marketing and Research Board Symposium on March 29, 2017 in State College, PA, and winemakers are encouraged to attend.
Some hydrogen sulfide or sulfur-containing off-odors can sometimes be mediated with use of fresh lees stirred in the wine or the addition yeast lees-like products. Winemaking products like Lallemand’s Reduless, yeast hulls, or some cellulose-based products can help reduce or eliminate the intensity of these off-odors. As with any other product additions, it is recommended that wineries always do bench trials first and before adding to the entire volume of wine. Additionally, Enartis USA (Vinquiry) has previously distributed a fact sheet to help winemakers troubleshoot reduced wines and determine how to best treat a problem wine.
The incidence of reduction, sulfur-containing off-odors, or hydrogen sulfide can be a frustrating circumstance for winemakers. However, adequate vineyard care and proper nutrient management during primary fermentation can help minimize the incidence rate of sulfur-containing off-odors from occurring in their wines. Of course, problems with wines do occur, and we hope that the recommendations above will help winemakers solve wine problems pertaining to sulfur-containing off-odors.
Jastrzembski, J. and G. Sacks. 2016. Sulfur Residues and Post-Bottling Formation of Hydrogen Sulfide. Appellation Cornell, 3a.