Evaluating Value Added Grape Seed Oil Research Project for Sustainable Viticulture
Evaluating Value-Added Grape Seed Oil Research Project for Sustainable Viticulture
For the 2012 grape harvest, we were able to obtain the pomace from approximately 48 tons of whole grapes. Each weekend from the first week of August until the first week of October, we obtained and processed the pomace from approximately 5 tons of whole grapes. Many best practices and lessons were learned during this first year of researching the feasibility of producing grape seed oil. The most difficult and first major step in producing grape seed oil is separating the seeds from the skins. Since this research project is a 2-year study to determine the feasibility of producing grape seed oil as an independent winery or as a regional cooperative, this first year was processed entirely by hand using inexpensive screens we fashioned for the purpose (screen construction described below). The use of hand-made screens holds down entry costs but increases labor. This type of screening would be appropriate for an individual winery wanting to produce grape seed oil from just their own grape pomace. The entire 2013 harvest will be processed using a corn seed cleaner repurposed as a trommel for separating the seeds from the skins. We expect this process to significantly reduce the labor but will increase entry costs. This type of screening would be appropriate for a regional cooperative that is processing the grape pomace from several regional wineries.
Initially our plan involved immediately drying the pomace before separating the seeds from the skins. However, the first batch that we processed in this manner proved that this step was wrought with several problems. First, attempting to dry the pomace with the seed and skins together required significant energy to remove the added significant moisture from the pomace. Further, from our experience, we found it was more difficult to separate the dry pomace especially when dealing with white grape pomace.
During the process of making white wine the juice from white grapes are immediately pressed and the skins and seeds do not go through fermentation. This results in white grape pomace that is saturated in grape juice and is therefore very sticky. When this pomace is dried the seeds are now stuck to the skins. We needed to re-wet the pomace in order to get any significant separation. After this initial setback, we determined it was better to immediately separate the seeds from the skins without drying them first. The stickiness of white grape pomace is still an issue and results in significantly less seeds being separated than what can be obtained from red grape pomace.
During the process of making red wine the grapes are crushed and the resulting juice, seeds, and skins are all fermented together. The fermentation process consumes most of the sugar and as a result when the seeds and skins are pressed from the wine the pomace is significantly dryer and less sticky than white grape pomace. While not attempted this year, we believe it may be possible to increase the yield from white pomace by rinsing the pomace with water and then pressing off the liquid to remove much of the stickiness. Averaged over the season, we were able to obtain approximately 70 lbs of seed from each ton of red pomace and approximately 50 lbs of seed from each ton of white pomace.
In order to separate the seeds from the skins we created a hand screen out of 2×2 lumber and 1/8 inch screen from the local hardware store. The screen measures 36 inches X 48 inches and was fashioned to fit on top of one of the macrobins purchased for this project. The macrobins were distributed to each participating winery for them to place their pomace. The use of macrobins proved to be crucial to any regional effort to obtain pomace from participating wineries. Most wineries only have enough macrobins to serve their purposes. With an average turnaround time of 3-4 days to process the pomace and return the macrobin to the winery, it would negatively affect their operations. Supplying them with macrobins will probably result in higher participations rates.
After wineries would press their grapes they would place the pomace into our bins and then they would let us know they were ready to be picked up. When the pomace arrived at our facility, the macrobin would be placed next to an empty macrobin. The screen would be placed on top of the empty macrobin and the pomace would be shoveled onto the screen. Usually about 3 or 4 full shovels would place an adequate amount of material for the screen. At this point 2 individuals would shake the screen back and forth similar to how screens are used at an archaeological dig. As the screen is shook the seeds fall through the screen and the skins remain on top. We estimate that the screen achieved about a 90 percent separation rate with a few skins making it through the screen. Once the majority of seeds had fallen through, the remaining skins would be dumped in a pile to later be discarded. These steps would be repeated until all the pomace had been processed. Averaged throughout the season, it took approximately 2 hours to process each ton with less time and effort required for red pomace versus white pomace.
Once the seeds are separated it is essential that they immediately begin drying in order to stabilize the seeds for preventing microbial and chemical degradation and producing seeds suitable for oil extraction. For this first year, in order to hold entry costs down, we simply spread the seeds out on tarps to dry in the sun. We found that this worked remarkably well, reducing the moisture level of seeds from an average 60 percent to 70 percent to around 30 percent after just 2 days in the sun. The labor required for this step was not significant but is dependent on cooperative sunshine. Also, this drying process required some supervision to ensure the seeds were not disturbed by animals or to be quickly gathered up if it appeared rain was imminent. Periodic raking of the seeds also helped the drying process but was not critical as long as seeds were spread no thicker than 1/8 inch deep. At dusk all the seeds were gathered up and stored inside. The use of tarps made this a quick and easy process. The corners of the tarp can be lifted which keeps all the seeds in the tarp and then can be lifted or dragged inside. In the morning the tarps (with seed inside) are replaced in the sun and seeds are quickly spread out again. We have no doubt that seeds could be completely dried in the sun with a few more days and cooperative weather. However we wanted to see if we could speed this process up without significantly increasing the entry cost for an individual winery operation. After a little experimentation we identified a couple of steps that work well and the equipment required is still modest.
After drying in the sun for 2 days the seeds (and some skins) are significantly dryer and were then placed into a plastic cement mixer purchased for this purpose. With the seeds tumbling in the cement mixer a leaf blower was pointed at the mixer which does an excellent job of blowing out dust and any remaining skins. The leaf blower helps to reduce the moisture level a few degrees but typically the seeds are still too moist for safe storage. Based on our research we felt it was important to get the seeds below 15 percent moisture in order to be stored until pressing for oil. We used a grain moisture meter to ensure accurate readings at this critical stage. To complete the drying process we placed the seed into 60 gallon plastic barrels and used a common corn grain bin dryer that was purchased from the local Tractor Supply. The dryer is essentially a long tube perforated with holes its entire length with a fan attached at the top that pulls air from the holes in the tube. The tube was placed in the center of the plastic barrel and then the seeds were placed around it. These grain bin dryers are intended for the significantly larger grain bins found on many farms so it can dry the seeds in a plastic barrel rather quickly, typically in a day or two depending on the moisture starting point and whether placed in the sun. With the barrel placed in the sun the dryer works very quickly. However, we discovered that the seed still needs the initial 2 days of drying in the sun before being placed in the barrel. When we attempted to go straight into the barrel, avoiding the 2 days in the sun, we found that we would get stratified layers within the barrel that did not dry evenly. It is important to get the seed down to approximately 30 percent moisture before placing into the barrel.
Impacts and Contributions/Outcomes
For both the separation and drying process, we believe many additional efficiencies could be realized. However, our method proved 5 tons per weekend, which is more than most wineries in our area process, can reasonably be achieved without significant entry costs. For the 2012 harvest season, we ended up with a little over 3000 pounds of grape seed from approximately 48 tons of whole grapes. The seeds will be pressed for oil during the summer of 2013. We had originally planned on pressing the oil immediately after drying but the press we ordered was put on back order from Germany and did not arrive until cold weather had set in. We were advised by the manufacturer that we would get a better yield if we waited until summer to process the seed. While our press is considered a cold-press (no external heating added) which produces the highest quality oil, the temperature of the seed does impact yield. At 70 lbs of seed per gallon, we are expecting around 42 gallons of extra virgin grapeseed oil from the 2012 season. For the 2013 season we expect to reduce our labor and increase our yield of both grapeseed and grapeseed oil based on improved efficiency expected from the trommel (repurposed corn seed cleaner). Our final report will cover both the 2012 and 2013 harvest seasons and will compare and contrast business models of an individual winery and a regional cooperative. Spreadsheets for both business models will clearly identify all costs and potential profits.
Prairie Crossing Vineyard
31506 Pioneer Trail
Treynor, IA 51575
Office Phone: 7124873812
60373 Kidd Rd
Glenwood, IA 51534
Office Phone: 7125273356
63966 250th ST
Glenwood, IA 51534
Office Phone: 7125275276
60697 Kidd Rd
Glenwood, IA 51534
Office Phone: 7125272188
ISU Extension 7 Outreach
415 Main St
Malvern, IA 51551
Office Phone: 7126248616
Country Air Vineyard
60697 Kidd Rd
Glenwood, IA 51534
Office Phone: 7125272188