| | | | Reminder to sign up for the following multi-state webinars in collab with Dr. Watrelot!
 Regional viticulture and enology specialists will present a Grower and Winemaker Town Hall virtual meeting series to give seasonal updates and answer pre-submitted and live questions from grape and wine industry stakeholders. The structure of these meetings depends on pre-submitted questions. Use this link to pre-submit questions for viticulture and enology specialists to answer live during the meeting. Please feel free to submit questions related to any topic by July 6th. But please see below for the topic area suggestions for the July 13th meeting. Viticulture focus area: post-fruit set to veraison (crop load management, canopy management, pest management, nutrient management, mechanization of vineyard operations) Enology focus area: primary fermentation (harvest decisions, fruit chemistry analysis, and fermentation options, e.g. non-Saccharomyces yeast, strain selection, ambient ferments) Register using this link and choose your breakout room (viticulture or enology) for the July 13th meeting. After registering, you will receive a confirmation email containing information about joining the meeting.
The Research and Winemaking webinar series is back! This series started in August 2020 and 7 topics related to winemaking were covered from cleaning and sanitation to bottling with the participation of industry and academic partners. Past recordings can be found here.
This year we decided to go more in depth into specific topics including enzyme, yeast, microbial spoilage, sorbic acid, bentonite and tannins. These FREE 90-minute webinars will start in June and are being offered monthly through December to the grape and wine industry members who are using mostly hybrid and climate-adapted grape varieties. The webinars are co-organized and co-hosted by Dr. Aude Watrelot, Assistant Professor of Enology at Iowa State University and Drew Horton, Enology Specialist at the University of Minnesota's Grape Breeding & Enology Project.
July 6th: Yeast selection
August 3rd: Microbial spoilage
October 5th: Sorbic acid (sorbate) management
November 2nd: Bentonite treatments
December 7th: Enological tannins
Yeast selection
During the 90-minute webinar on July 6th at 3PM Central Time, Tom Mondor (Gusmer Enterprises) will present and discuss practical approaches in selecting the appropriate yeast for different styles of wine. Dr. Anna-Katharine Mansfield (Cornell University) will discuss the research approach on the selection of yeasts for cold-hardy grapes as part of the past Northern grape project.
Register Here!
For further details or any questions, check out the Wine Industry Events in Dr. Watrelot's website https://faculty.sites.iastate.edu/watrelot/ or contact us at watrelot@iastate.edu and dhorton@umn.edu | | | Defining Spoilage Maureen Moroney
What is a spoilage microbe?
When it comes to wine microbes, a lot of times we think about splitting them into two categories: "good" and "bad." In the simplest terms, we think of Saccharomyces cerevisiae as the "good" yeast and we think of Oenococcus oeni as the "good" bacteria, and pretty much everything else is considered "bad."
What makes a microbe bad?
If we think about microbes in society, we're used to thinking about germs that have a negative impact on human health. Similarly, a spoilage organism in wine can be defined by the undesired characteristics it causes. Uncontrolled acetic acid bacteria lead to unpleasant vinegar aroma, Brettanomyces yeast contamination leads to smoky/leather/manure/medicinal aromas, and so on. In contrast, "good" yeast and bacteria are the ones that do what we want – namely, they efficiently convert sugar to alcohol or convert L-malic acid to L-lactic acid – with minimal unwanted effects.
Sensory impacts of wine microbes
We've all learned that a good wine yeast, typically S. cerevisiae, performs the following conversion through a series of reactions:
C6H12O6 (glucose) à 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)
But it turns out it's a lot more complicated than that, because this main pathway involves many intermediate compounds that can branch in lots of possible directions and form other products.  | | | Pre- fermentation Juice Clarification Jennie Savits Juice clarification is a technique primarily used in the production of white and rosé wines. The goal is to reduce excess suspended solids to an acceptable range (0.5-1% v/v) prior to fermentation. Solids can be measured as turbidity units where a recommended range is 50-250 NTU (nephelometric turbidity units), depending on cultivar. Removing excess solids such as pulp and skin fragments cuts down on the oxidative enzyme polyphenol oxidase, which causes enzymatic browning. Additionally, clarification of juice helps minimize development of volatile sulfur compound odors (e.g. hydrogen sulfide and the like), decrease herbaceous aromas, and can lead to increased delicate/fruity aromas. Achieving a target solids level is important because over-clarified juice may lack the nutrients needed for a healthy fermentation. Methods to clarify juice include cold settling (static), flotation, or centrifugation: - Static cold settling involves chilling the juice down to 35-40F for 24-48 hours. The force of gravity settles out solids, while the cold temperature helps stave off spontaneous yeast fermentation. Clear juice is then racked off the gross lees. Drawbacks include chiller tank capacity and load, time, and potential for oxidation.
- The flotation method provides settling somewhat in reverse of the static method. Juice treated with fining agents is subjected to micronized nitrogen gas bubbles pumped from the bottom of the vessel. The gas bubbles 'stick' to the flocculate, artificially lowering the density and floating the lees (termed flees) to the top. This flees requires around 10% headspace availability in the tank. The clear juice is then racked from the bottom of the tank. Flotation is quicker and more efficient; in that it reduces juice loss and can be done at ambient temperature.
- The centrifugation method employs centrifugal force to speed up settling, 100-1,000 times faster than would occur naturally by gravity. A decanting centrifuge is the type most often used for juice; where the force separates the denser solids outwards against a rotating bowl while the clear juice forms a concentric inner layer. This type is preferred for juice clarification and lees filtration because it can handle the high levels of solids in juices. Centrifuges are generally found in large scale operations.
Fining  agents such as enzymes, PVPP, bentonite, or animal proteins (e.g. gelatin, casein), are often employed in conjunction with these methods to improve clarification. As noted above, a combination of them are required for the flotation. One resource specifically mentions enzyme treatment followed by bentonite and gelatin. Due to the structure of pectin, unripe or high pectin-containing have increased juice viscosity making clarification more difficult. Products containing a preparation of various enzymes work to breakdown pectin structures at different points, thus improving clarification. Following up with a bentonite addition improves clarification and provides protein stability. Recommendations for product type, addition timing, and addition rate of bentonite vary, as overuse may impact aromas and flavors. Gelatin additions help to improve the floc and adhesion of bubbles to it. Determining which method is best depends on a variety of factors including size of operation, equipment availability, time, costs, and labor. Static cold settling is commonplace in wineries of various sizes. Centrifugation has often been used in large scale operations due to cost of equipment. Flotation was first used in Australia for winemaking and has become popular more recently due to improvements in the technology. It has been more common in large scale operations, however equipment is available for a winery of any size. Resources
AWRI. Winemaking Treatment-Juice CLarificaiton by Flotation. Accessed 20 June 2021. Available at: https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-juice-clarification-by-flotation/
Howell G and Gamble C. 2016. Flotation for Wine Clarification – How Does it Work and Why Use It? Vintessential Laboratories. Accessed 21 June 2021. Available at: https://www.vintessential.com.au/flotation-for-wine-clarification-how-does-it-work-and-why-use-it/
Jackson RS. 2014. Fermentation. In Wine Science Principles and Applications (ed. 4) pp. 441-442. Academic Press, San Diego, CA.
Karasek J. 2020. Rapid Clarification: Tips and Tools for Clarifying Juice and Wine During Harvest. Accessed 18 June 2021. Available at: https://www.enartis.com/en/video-and-webinar/rapid-clarification-tips-and-tools-for-clarifying-juice-and-wine-during-harvest/
Reynolds AG. 2010. New Directions in stabilization, clarification and fining of white wines. In Managing Wine Quality (vol. 2). pp. 188-225.Woodhead Publishing, Philadelphia, PA. | | Through the Grapevine
We are taking a look at some of Dr. Dharmadhikari's published articles, as they are a great resource and a way to freshen up on some of the obstacles we often see with harvest wine production .
Harvest Preparation- The harvest season is around the corner. This is the busiest and the most critical period of the year. Organizing the crush and careful planning of this work is essential for a successful and trouble-free vintage. Let's consider several topics to help you with the upcoming vintage. Cleaning and sanitizing during processing is very important keep an adequate supply of cleaning materials such as industrial strength detergents, sanitizers, and hot water. Brushes, brooms, squeegee, etc., may seem like minor items, but they are essential to do a good cleaning job. Inside the winery check the floor for cracks and low spots (where water or juice may accumulate) and repair them. Postponing any repair will make the problem worse. Check the walls and ceilings for mold growth and other foreign material and clean them well. Make sure the cellar has good ventilation. You may consider having a fan on hand to create an air curtain to keep fruit flies away. This is important not only for producing quality wine, but also for creating a positive impression of your operation if it is open to visitors. Equipment used during crush such as the crusher, press, pumps and others should be checked to make sure they are in working order. They should be tested and repaired, if needed. Breakdown of key equipment, such as crusher, press, pumps, chillers, etc., can be disastrous. It is therefore crucial to see that the equipment is in sound working condition. CONTINUE READING
Previously published in Vineyard & Vintage View, Mountain Grove, MO | | | Let's focus on.. with Dr. Watrelot | | | | Focusing on Research Winemaking
Ongoing Research Project Grape Pomace Did you know that over 71% of grapes produced in the US are processed to make wine? Also, that the production of wine leads to about 20 to 25% of the total processed grapes being pomace? The increase of wine consumption and wine production automatically increases the production of grape pomace. Pomace is a biodegradable solid by-product containing seeds, skins, stems and remaining flesh particles obtained after must pressing during the winemaking process. In addition to the high percentage of water, sugar, fiber, proteins and lipids, grapes contain phenolic compounds. These compounds are known for their health benefits including antioxidant and anti-inflammatory properties reducing the risks of cardiovascular diseases and cancers. During the winemaking process, the extraction of phenolic compounds from grape skins and seeds is far from being complete due to the skin size, seed structure and flesh chemical composition. Therefore, after pressing, about 50 % of tannins, the polyphenols are responsible for astringency perception. Between 15 to 60 % of anthocyanins, polyphenols are responsible for red wine color remained in grape seed and skin pomace from Grenache, Syrah, Mourvedre, Alicante Vitis vinifera grapes (Ky & Teissedre, 2015). Grape pomace, is either dumped in the fill or used as compost but due to its high moisture content, pomace can be perishable, lose its antioxidant properties and bring some diseases and insects into the vineyard or field if it spread out. During the past years, novel extraction techniques have been developed to add a value to this waste by extracting either oil, lipids, vitamins and antioxidant compounds from seeds and/or fibers and phenolic compounds from skins. In order to add a value to cold-hardy grape pomace, a former colleague from ISU (Dr. Venkitasamy) and myself decided to develop a method to appropriately dry grape pomace before grinding and using flour which would help remove any microbial risks, reduce the risk of polyphenol oxidation and improve the antioxidant activity. This research project has been funded by the USDA-AMS Iowa Specialty Crop Block Grant and started in October 2020.   Figure 1 Grape pomace before drying Figure 2 Grape pomace after IR drying CONTINUE READING | | | | CHECK OUT BEFORE YOU GO... | | | | A new (FREE!) fact sheet series is live on the Iowa State University Extension Store. The series provides information on the combination of methods used to estimate grape maturity as harvest approaches: Check it out! | | | | | | | | |
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