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February Issue
Upcoming Events!

Oxygen Management Workshop
March 4, 2020

Sign up to learn about how to improve your wine’s shelf life, reduce spoilage, and better manage inert gas and sulfur dioxide use in the winery.  This is a one-day workshop featuring Luke Holcombe of Scott Laboratories, as he shares knowledge and experience in managing oxygen throughout the winemaking process. Workshop registration includes lunch, course materials and hands-on demonstrations and activities.

For more information and registration 
http://www.aep.iastate.edu/oxygen/index

Winemakers Roundtable- Red Blends
March 9, 2020

SPACE IS LIMITED to the first 12 interested winemakers for our series of Iowa Winemaker's Roundtable events we'll be hosting over the course of the upcoming year. We are requiring a minimum of five winemakers confirmed to participate in order to host these events around the state, so feel free to invite your neighboring winery colleagues!

More info: click here
Overview and Current Research on Grapevine Trunk Diseases
Maureen Moroney
 
With spring around the corner, and heading into busy pruning season, many growers have questions about Grapevine Trunk Diseases (GOVeTD). Let’s review some background on these diseases, how worried we should be, best practices for prevention and management, and some possible future research and resources.


Pathogens and symptoms
  • Fungal diseases
  • Should be regarded as a complex of pathogens, including the causative agents of Eutypa dieback, esca, and Botryosphaeria dieback
  • Symptom expression varies from year to year, and among grape varieties, making it difficult to identify characteristic disease symptoms
  • Fungal pathogen plugs xylem and phloem, impairing movement of water and nutrients
  • Wood decays, grapevine declines
  • Grape yield and quality are affected
 
Infection cycle and disease progression
  • Infection primarily through pruning wounds; pruning period has highest risk of infection
  • Wounds remain susceptible to infection for several weeks
  • Fungal spores become airborne during and after rain events
  • Each vine can be infected multiple times with one or more pathogens
  • Slow movement through vine, long incubation times
Management options
  • Overall approach: Delay establishment and minimize impact
  • Try to prune in dry weather, when there is less airborne fungal inoculum – this may not be possible
  • Double pruning (early pre-pruning and final pruning closer to budbreak)
  • Sanitation of pruning equipment (e.g. after each row)
  • Fungicide application to pruning wounds
  • Coverage/protection of pruning wounds with non-fungicidal substance
  • Remove infected portions of the vine
CONTINUE READING
Has the future of cold stabilization arrived?
Jennie Savits
Cold stabilization is a production technique used to remove the potential for potassium bitartrate (KHT) crystal formation and precipitation in finished product. The precipitate, commonly known in the kitchen as cream of tartar, causes no harm to consumers but is generally considered aesthetically unpleasing in bottled wines. Thus, KHT is proactively removed during wine production. Wine is chilled to just above its freezing point to simulate the conditions if a wine was stored in the fridge, the crystals can form and precipitate out in the tank rather than in bottle. 

Tried and true techniques to achieve cold stability include chilling or contact process. In the chilling process, wine is held at 26-28°F for up to a month. The process includes both stable temperature and time to precipitate. The contact process involves seeding a chilled wine with fine potassium bitartrate powder (4g/L) and agitation followed by settling. The seeding and agitation speed up the process. These both work to remove KHT but may overexpose wine to oxygen, take quite a bit of time, and be costly to wineries in terms of energy and space - to hold, chill, warm, and/or mix the wine.
 
More recently, products have come to market to with the intention of inhibiting the precipitation from occurring. The primary action of these products is to eliminate nucleation sites or coat the KHT to prevent crystal growth. The nucleation site is the point where a crystal first begins to arrange in a pattern and where further particles can attach. Examples of inhibitor products are carboxymethyl cellulose (CMC) - a cellulose gum, yeast mannoproteins, metatartaric acid, and gum arabic – a mixture of saccharides and glycoproteins. These products may work but each comes with a set of parameters for optimum results. Timing of addition, alcohol content, conductivity in a specific range, use of other fining agents, and temperature all factors that can affect the effectiveness of the products.
In early February, Enartis USA announced a new set of products they deemed ‘revolutionary’ for tartrate and color stability. The products are now TTB approved and available for sale the US. Zenith Uno  and Zenith Color contain potassium polyaspartate (KPA). KPA is the potassium salt of a polyamino acid from the amino acid L-aspartic acid. L-aspartic acid is a naturally occurring amino acid in wine. Uno is recommended for all wines while Color also has gum Arabic to assist with anthocyanin stabilization for reds.

CONTINUE READING
New Insight for Tannins in Red Hybrids from Recent AJEV Article
Erin Norton
A recent publication in the American Journal of Enology and Viticulture from the Mansfield group at Cornell University details some important results dealing with tannin and some of the current issues we see in winemaking with our cold-hardy hybrids.

The overall goal of the study was to investigate the addition of exogenous tannin to must and the subsequent retention of those tannins in the final wines.
Before explaining the experimental details of the winemaking, it’s important to highlight some of the initial experiments they did to determine the actual tannin concentration in commercial grape tannin products available.  In the publication none of the products were identified.  The researchers measured the amount of tannin in 1g/L of powdered product.  What they found is presented in Table 1.
These results emphasize that tannin products are not pure, and contain many other types of compounds that were extracted from grape skin or seeds depending on the product.  Winemakers need to be aware of this “extra” fraction of compounds that is being incorporated into their wine.  It could have sensory effects in aroma/flavor or taste.  These effects may not be negative, but winemakers should be aware of the additional sensory changes besides just structure.  I did a quick search, on grape tannin products, and no companies are detailing the purity of their product.
 
That leads to the real experiment that the researchers did.  Working with Maréchal Foch (French-American hybrid), Corot Noir (Cornell-Geneva hybrid) and Cabernet Franc (Vitis vinifera) tannin product was added to the must at 3 different addition rates: 400mg/L, 800mg/L or 1200mg/L.  It should be noted that the normal maximum recommended commercial dose to red must (based on my quick search results) ranges from 100mg/L to 400mg/L depending on the product.  Therefore the researchers were adding a significant excess to the must.  The retention of the tannin in the final wines is illustrated in Figure 2.  Visually it can be seen that Maréchal Foch had much less retention of the added tannins than the Corot Noir or the Cabernet Franc.  One conclusion from this is that hybrid cultivars do behave differently and should probably be evaluated individually.  Maréchal Foch is also much more cold-hard than Corot Noir, and this result of low tannin retention in a more cold-hardy cultivar is supported through other works from the Sacks group at Cornell, the Pedneault group in Nova Scotia and here at ISU.
CONTINUE READING
Smoke Taint
Somchai Rice, Ph.D.
News of wildfires and bushfires from around the world are, of course, devastating.  I want to take this opportunity to discuss smoke taint and how it can affect vineyards, and ultimately, the wines we love - even here in Iowa.

Although smoke-related volatile phenols can accumulate on all plant surfaces, recent studies have shown that the point of entry is fastest directly through the berry cuticle and slow from absorption through the leaves.  These volatile phenolic compounds are in Table 1.  It only takes one exposure event to result in ‘smoke tainted’ wine, with repeated exposures showing an additive effect.  This exposure can include controlled burns or agricultural burns. When these compounds enter the berry, a chemical reaction happens to bind them to sugars within the grape.  This reaction essentially ‘holds’ the smoky odors in the grapes and wine until they are cleaved from the sugar.  This separation happens either during fermentation, over time in barrel or bottle, or during consumption of the wine.  It should be intuitive, then, that the stage of grapevine growth and berry development directly affects the uptake of smoke taint compounds from wildfires or controlled burns near the vineyard.  Berries that are post-veraison through harvest are at most risk for smoke taint.  The rate of absorption is dependent on the variety, with Sangiovese more sensitive than Cabernet Sauvignon.  Currently, there is no data available for the uptake of smoke taint compounds with regards to the cold-hardy hybrid varieties popular in the upper Midwest.

Sources:
Krstic, M.P., Johnson, D.L., Herderich, M.J. 2015. Review of smoke taint in wine: smoke derived volatile phenols and their glycosidic metabolites in grapes and vines as biomarkers for smoke exposure and their role in the sensory perception of smoke taint. Aust. J. Grape Wine Res. 21(S1): 537-553.

Fact sheet available at https://www.awri.com.au/wp-content/uploads/2012/04/smoke-taint-entry-into-grapes-and-vineyard-risk-factors.pdf
 
Fact sheet available at https://www.awri.com.au/wp-content/uploads/2018/06/controlled-burns-fact-sheet.pdf

 
Let's focus on.. with Dr. Watrelot

Focusing on Research winemaking
 
Oxidation in White Wine
 
In the previous newsletter of December 2019, the principle and consequences of oxidation in red winemaking have been discussed. To provide a full overview about the mechanisms of oxidation occurring in wines, the oxidation in white is the topic of this research focus.

An oxidized white wine is usually attributed to the change of the yellow color, to the production of acetaldehyde and to an increase of the bitterness. But in some white wines, the oxidative character is considered desirable, e.g. Vin Jaune from the Jura region, France. These wines are aged under a yeast bloom acting as an oxidation-reduction buffer and preventing excessive oxidation as well as producing acetaldehyde and ethanol.

In other types of wine, this oxidized impression is not considered acceptable. Two mechanisms of oxidation exists: enzymatic and non-enzymatic or chemical oxidation (Oliveira et al., 2011). The chemical oxidation mechanism is not explained in this article.

  

   

Figure 1. La Crescent (LC) (left) and Brianna (B) (right) white wines freshly opened (left top and bottom pictures) and after 3 days (right top and bottom pictures).

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Focusing on a Grape Variety
La Crescent
La Crescent is named after a small town in the state of Minnesota and also named MN 1166 which is a light-skinned hybrid grape variety developed by the University of Minnesota and released in 2002. It has a very complex ancestry, including 45 % Vitis vinifera, 28 % Vitis riparia, 10 % Vitis rupestris, labrusca and aestivalis and is the result of the cross of St Pepin × unnamed Elmer Swensen (ES 6-8-25)(Luby, 2012).

This grape variety has a cold hardiness of very hardy (-20 to -35 F) and has different levels of sucsptibility to disease. La Crescent has a low susceptibility to Botrytis bunch rot, crown gall, Eutypa dieback and Phomopsis cane and leaf spot (1, 3), a moderate susceptibility to black rot and powdery mildew, and a high susceptibility to anthracnose. McManus et al., 2017 showed that La Crescent was sensitive to copper fungicide after 6 applications of copper (2.722 g/ 378.5 L), and sensitive to sulfur after 5 applications of sulfur (3.629 g/ 378.5 L). The injury on leaves due to copper is more severe when the leaves remain wet for long periods of time and the sulfur injury is promoted by high temperatures. In vineyards from Minnesota state, the yield per vine from mature vines on 6- or 8- foot spacing is about 6.17 kg (Clark et al., 2017) and varied from 5.0 to 8.5 kg/vine in 2015 and 2016, respectively in La Crescent vineyards from Wisconsin state (Scharfetter et al., 2019).
CONTINUE READING

ISU Viticulture Weather Station Reports

From our Ag Specialist Jim Schrader
available online at https://www.extension.iastate.edu/viticulture/


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