Project Overview
Annual Reports
Commodities
- Fruits: grapes
Practices
- Crop Production: food product quality/safety
- Farm Business Management: value added
- Sustainable Communities: sustainability measures
Proposal summary:
Contrary to accepted practice, washing grapes to remove residual pesticides and other contaminants may not compromise wine quality by diluting or otherwise altering pulp compounds protected by the relatively impermeable berry skin.
Project objectives from proposal:
The North Central Region is recognized as the most difficult multi-state area of the United States for growing vinifera (European/California style) grape varietals for winemaking. The combined conditions of extremes of temperature and humidity along with a short growing season account for much of this problem. The exceedingly high fungal disease pressure exacerbates this situation. It is not surprising then that there are no commercial winegrowers making organic wine from organically-grown grapes in the Ohio River Valley, which until 2008 was the largest American Viticulture Area (AVA).
Beginning in 2006 our research station has tried every combination of Organic Materials Review Institute (OMRI) approved means for organic grape growing in a quarter-acre test plot set aside for that purpose. Neither ionic copper (Kocide3000TM) or sulfur (MicroThiolTM), nor microbiological (SerendadeTM), nor immunological stimulant (RegaliaTM) commercial OMRI-approved products have been effective against the extremely high disease pressure of this area. Moreover, contrary to Internet and anecdotal claims, so-called “home remedies” such as soaps, baking powder, vinegar, milk, and natural oils have been equally ineffective. Six years of unsuccessful trials pitting organic measures against the region’s fungi population has convinced us that vineyards within range of the Ohio River’s morning fog are not suited for organic growing of either vinifera or French-American hybrid grapes.
By necessity then, commercial winegrowers of this extensive region continue to disperse synthetic fungicides to control black rot, phomopsis, anthracnose, and both powdery and downy mildews. The Environmental Protection Agency of the federal government regulates the use of synthetic pesticides according to the manufacturers’ specifications for application quantity and frequency, protective clothing (and in some cases breathing apparatus) to be used, post-application vineyard restricted entry interval (REI) and pre-harvest interval (PHI) (1). However, no monitoring or inspections of pesticide use is conducted at any level other than the record-keeping of the grower. Wineries and consumers are completely dependent on the manufacturers’ safety claims and on the conformance of the grower to the manufacturers’ prescribed dosage.
Having conceded that our farm’s site is not suited to organic grape production, we have researched the various synthetic fungicides to settle on ethylenebisdiothiocarbamate (EBDC) for future trials. Grape growers in the NCR SARE region have effectively used EBDC for fungi control as far back as the 1940’s (2). Present trade names under CAS Registry No. 8018-01-7 include Mancozeb TM, Aazimag TM, Fore TM, Dithane M-45 TM, and Manzate 200 TM (3). It is significant to recognize that whereas the manufacturers of EBDC are quick to point out that their products have negligible vapor pressure and are quickly hydrolyzed with a half-life less than two days, it is thanks to independent researchers that we are made aware of the breakdown products of EBDC’s, one of which (ethylenethiourea) is classified by the EPA as a group B2 probable human carcinogen having caused cancer in experimental animals (4).
Given this quandary whereby carcinogenic byproducts of synthetic fungicides are tolerated for effective control of fungi, washing of wine grapes to remove pesticides immediately comes to mind. Unfortunately winemakers consider grape-washing to be an unacceptable practice. It is taken as gospel that the sugar content (Brix) as well as fruit pulp flavanols would be diluted, thereby adversely affecting the sensory quality and salability of the wine.
It is well known that fruit quality is compromised by rainfall immediately prior to harvest. Winegrowers typically measure the parameters of Brix, pH, and total acidity on a daily basis within one week of harvest, so they know the undesirable effects of rainfall occurring at this time. We believe that this observation results from the systemic uptake of water rather than the trans-membrane movement of water through the relatively tough grape skin cuticle. Preliminary results testing these parameters on grapes soaked in water for various time periods suggest that this is indeed the case.
This project intends to address all concerns of the local winemakers from whom we have solicited comments and criticisms. Rightfully, regional winemakers have been quick to point out that hand-washing of whole clusters under laboratory conditions is quite different from the rough treatment grapes undergo during harvest and transport to the sorting table for additional handling. Thus we believe that design and development of a grape-washing apparatus to be tested under field conditions is warranted. Likewise, vineyard spray treatments must conform to the local regimens which utilize a full spectrum of synthetic fungicides, surfactants and oils.
Following harvest and crush, but before fermentation starts, the sugar content (Brix), hydrogen ion concentration (pH), and total acidity (TA) will be tested. These are the three most commonly measured parameters influencing a winemaker’s subsequent cellar operations. This standard practice will be adhered to throughout the project’s parallel batch processing. The control batch parameters will be compared to those measurements made on the test batches. The test group will in all instances be handled identically to the control batch. The only difference will be the elapsed wash time of each test batch. To start, 5, 10, and 20 minute wash times will used. If no significant difference in measured parameters is found, then successive wash times will be doubled (40, 80, 160 minutes) until a change due to washing is observed. If at any time there is a significant difference in measured values, then that particular test will be repeated. On verification of change, additional longer wash times will be used to test the extent and linearity of the compromised treatments.
Because it is important to conduct this experiment under field conditions, a prototype grape washing apparatus will be constructed. The test fruit clusters will first be dumped into a wash basin and for the prescribed wash time will be buffeted about by a motorized filtration system. At the end of the wash time, the grapes will be removed from the wash solution by a hand-operated conveyor and allowed to dry under forced air during which time a control batch will be dumped directly into the stemmer/crusher and processed as usual. The washed test batch will then follow through the identical stemmer/crusher processing. While the next test batch is undergoing its wash time, the Brix, pH, and TA will be measured for the previously handled control and test batches. This procedure will continue until a significant difference in measured values is obtained. Also, to get an idea of how roughly the test clusters have been treated, for example skin bruising and breaking, wash solution samples will be collected after each trial. These solutions will be tested against saved standards used at the start of processing to determine if compounds have been leached from the washed grapes.
Sustainable practices will be followed. Water will be drawn from a rainwater rooftop collection system. Washing solutions will be recirculated and filtered for repeated use.