By Tim Martinson, Amanda Garris and Chris Gerling
Concord and Niagara grapes used for juice comprise the overwhelming majority of grapes produced in the New York and Pennsylvania Lake Erie belt. The challenge for Welch’s—wholly owned by over 1,000 grower-members of National Grape Cooperative—is to deliver consistent quality in its nationally-marketed juices from a crop that varies annually in size and composition and includes 150,000 to 170,000 tons of grapes from New York, Pennsylvania, and Michigan and an additional 100,000 tons from Washington State. Each year, the Welch’s team must adapt its blending and processing techniques in response to the season’s fruit characteristics as the intense, 40-day harvest period progresses.
While in the past processing issues were usually addressed in-house, Welch’s is increasingly teaming up with university experts such as Cornell faculty to deepen their understanding of the science behind processing issues. Leading the effort are John Pacheco, Welch’s director of grape technology and the newly-formed Grape Center of Excellence, and Jay Hardenburg, viticulture manager at National Grape Cooperative.
“When I came to Welch’s, we had limited resources and staffing for analytical projects,” said Pacheco. “Working with Cornell is complementary to the work we are doing in process development, but their mechanistic and flavor chemistry focus helps us understand our processing techniques better and develop more robust solutions to issues that arise.”
Two Cornell Food Science faculty – flavor chemist Gavin Sacks and processing technology expert Olga Padilla-Zakour, director of the New York State Food Venture Center – were enlisted to address juice quality and processing issues related to the color, flavor and aroma of Welch’s grape juice. The collaboration partially funded the work of two graduate students in Food Science and provided Welch’s with access to a fully-equipped pilot plant, advanced analytical equipment, and specialized expertise.
“Proximity to Cornell’s facilities meant we could harvest and process many small lots – without a 12 hour journey to our facilities in Concord, Massachusetts,” said Pacheco. “It added flexibility and extra capabilities we didn’t have in-house.”
The deep purple color of Concord is a key quality attribute for grape juice. Most juice is concentrated following production – and Cornell’s research showed that the processing method has an enormous impact on color retention.
“We knew that concentration before cold stabilization gave us better color in the juice, but we didn’t understand why,” said Pacheco. “Olga and Gavin conducted several grape chemistry experiments to determine why it works, and now we are confident about the reproducibility of this processing method.”
Graduate student Kristin Alongi, working with Sacks and Padilla-Zakour, found that when juice is concentrated before cold stabilization (a process called Direct to Concentrate or DTC), it retains more color than if the juice is cold-stabilized and then concentrated. Microscopic and chemical characterization identified the culprit: The anthocyanins (pigments responsible for color) precipitated out with the potassium bitartrate (cream of tartar) when cold-stabilization was performed on juice but not when it was performed on concentrate (see figure). Sacks and Padilla-Zakour believe this is because of pH differences between the standard and DTC practices.
“We now know the scientific basis for the color improvement, and we know it is not a cofactor that will be present in one year and disappear in the next,” said Pacheco.
With solid scientific grounding for the processing method, Welch’s has made new investments in DTC processing in its Westfield, N.Y., processing facility, resulting in an estimated $239,000 in savings during the first year, according to Welch’s annual report. Annual savings are expected to be significantly higher – and to dramatically increase processing efficiency at Westfield.
The color-conserving DTC process was particularly important during the warm, early 2010 harvest.
“The harvest was early and the grapes were ripe, and yet color was still an issue because of unusually warm nights in September,” said Hardenburg. “DTC helped us preserve the color we had, rather than losing some of it during processing.”
Expertise in flavor and aroma chemistry helped Welch’s with a flavor issue called ‘green note’ – vegetal aromas that sometimes appear in the grape juice during the first few months following harvest. Welch’s scientists and field staff knew that ‘green note’ was most prominent in cooler years, particularly during the crucial September-October ripening phase, but they did not know what the compound was, much less how to mitigate it.
“Although it dissipates with time, we initially see higher levels of consumer complaints, so we needed to identify the root cause and ways to control it either at the farm level or in processing to reduce consumer dissatisfaction,” said Pacheco.
Graduate student Meera Iyer, working with Sacks and Padilla-Zakour, determined that two compounds with herbaceous aromas, trans-2-hexenal and hexanal, are elevated in newly produced juices with green note characteristics. This has provided a new tool to determine when and why the ‘green note’ aroma occurs and why it fades during storage.
In experiments to see how processing methods affect the greenness in finished juice, Iyer found that levels of these two chemicals were much higher with ‘hot break’ processing than standard ‘hot pressing.’ They suspect that the higher heat levels in ‘hot break’ inactivated enzymes that would convert the ‘green note’ compounds into other compounds that are less odor-active.
According to Hardenburg, the presence of ‘green note’ is linked to annual weather conditions—it's more prominent in years with delayed ripening and later harvests—but it may also be becoming more common due to changing viticultural practices.
“As growers push the yield envelope higher and higher, it becomes more of an issue,” said Hardenburg. “We need to understand what practices in our growers’ vineyards contribute to greenness.”
Based on the work of Sacks and Padilla-Zakour, Welch’s and National Grape are supporting research by Cornell viticulture researcher Terry Bates, director of the Cornell Lake Erie Research and Extension Laboratory (CLEREL), to link vineyard practices and weather conditions to the production of grape volatiles, including the ‘green note’ compounds. By collecting grape samples at nine vineyards in western New York throughout the growing season, Bates hopes to track how vineyard practices and weather influence the volatile composition of juices, and whether these volatiles are correlated to other aspects of grape composition. Recent work by Sacks and Padilla-Zakour indicates that sugar concentrations close to harvest are not sufficient to predict the presence of green aroma compounds.
“Hopefully, key volatiles like the green note compounds will be correlated with other more easily-measured compounds such as acids, since measuring these volatiles requires specialized analytical equipment and is too expensive and slow for routine field measurements.” said Sacks.
Thanks to Welch’s donation of its idle GC/Mass Spectrometer to the CLEREL laboratory, Bates will have the specialized equipment needed to analyze samples for green note on-site in western New York over the 3 to 5 year duration of the project.
Welch’s is eager to apply knowledge of how vineyard practices and climate influence these grape volatiles to their annual task of harvesting and processing Concord and Niagara into high quality juice that commands a premium price.
“We’d like to be able to be proactive in planning harvest and tailoring processing and blending strategies to mitigate green note, rather than reacting to what we find at harvest,” said Pacheco. “Our ultimate goal is an annual map relating crop characteristics to specific microclimates within the grape belt that will allow us to fine tune harvest, processing and juice blending and better understand the links between vineyard variability and flavor/aroma chemistry.”
For Welch’s, a deeper understanding of processing issues – and how vineyard practices and weather influence juice quality – will have a direct impact on the bottom line.
“Welch’s established the Grape Center of Excellence in 2010 to better understand how Concord and Niagara fruit grape chemistry affects processing and juice quality,” said Pacheco. “We expect our collaboration with Cornell researchers to result in cost savings, increased processing efficiency, improved juice quality, and higher proceeds and net income for our grower owners.”
For the Cornell faculty the public-private partnership is much more than a way to fund graduate students.
“It’s very fulfilling when a project comes together where graduate students can apply science to real situations and learn industry impacts,” said Padilla-Zakour.
“You don’t have to sit and wonder if your work is having an impact. You get face to face confirmation that practices are changing as a result of your findings,” said Sacks.
Tim Martinson is senior extension associate in the department of Horticulture. Amanda Garris is a freelance writer, and Chris Gerling is enology extension associate in the department of Food Science.