The Challenge of Grape Marc
For centuries, winemaking has been an art form. But what happens to the by-products? When grapes are pressed to make wine, the leftover skins, stems, and seeds, collectively known as grape marc, can be a significant waste management challenge. While traditional methods like composting and livestock feed exist, they often come with their own set of issues. Stockpiling grape marc can release greenhouse gasses as well as create leachates into the soil. Composting can be a long process and may not efficiently return valuable nutrients to the soil in a timely manner. As the global winemaking industry mandates more sustainable practices, there’s a clear opportunity for improvement in waste management.
Enter Insect Bioconversion
This is where our specialty comes in. The Black Soldier Fly Larvae (BSFL) can effectively and efficiently convert organic waste streams into insect products (e.g., insect protein for animal feed) and frass (fertilizer) in a sustainable and environmentally responsible manner. Frass is the term for the larvae's excreta: it is rich in nutrients and beneficial microbes, making it a natural fertilizer with potential across a range of applications.
This technology has multiple benefits:
- Proximity to Source: Insect bioconversion facilities can be located close to the source of organic waste, which drastically reduces collection and transport costs.
- Fully Contained and Expedited: It's a quick and contained process for managing organic waste, which helps to mitigate social and environmental issues like odors and vermin.
- Dual-Purpose: It offers the supplementary production of insect protein, which is suitable for pet, aquaculture, and livestock feed.
Our Research and Key Findings
Our project with Penfolds and Schutz Barossa Vineyard tested a hypothesis: what if black soldier fly larvae could compost grape marc and return the nutrients to vineyards faster than traditional composting? To find out, we conducted a range of research activities, including preparing BSFL diets with different concentrations of grape marc, monitoring key growth parameters, and analyzing various samples. We studied 11 different diets that included three grape marc varietals: Sauvignon Blanc, Riesling, and Shiraz. The results were remarkable. We discovered that BSFL are not only fast but also highly efficient at composting grape marc. On average, 1 kg of BSFL can reduce 1.8 kgs of a substrate (containing up to 75% grape marc) to a compost standard in just 24 hours.
Other key findings include:
- Larvae Quality: The grape marc diet did not negatively impact the quality of the larvae, with their protein percentage remaining high.
- Nutrient Profile: The insect frass produced from the grape marc diet had a nutrient profile comparable to commercial vineyard fertilizer products. The average nitrogen content of the insect frass was 2.95% (DM), while the average carbon content was 48.7%.
- pH Transformation: Grape marc substrates with a pH level between 4 and 5 were increased to a neutral pH of 7 to 8 by the BSFL.
- Larval Growth: We found that larval growth rates were not significantly impeded by concentrations of up to 75% grape marc in their diet.
- Total carbon (C) in the resultant frass ranged from 46% to over 52%, confirming insect frass as an excellent source of carbon and nutrients for the growth of beneficial fungal and microbial populations in the soil.
Closing the Loop in Viticulture
The implications of these findings for the viticulture industry are significant. Insect bioconversion offers a novel "closed-loop" approach to grape marc management. The status quo of stockpiling grape marc is becoming increasingly unsatisfactory as it creates a range of negative social and environmental impacts. Furthermore, the demand for recovering and reusing organics in local winemaking regions is being seen as a necessary behaviour change to address the impacts of climate change and increasing fertilizer and other compost product prices. Instead of seeing grape marc as a waste product, it can be viewed as a valuable resource that can be rapidly converted and returned to the vineyard. This process returns essential nutrients to the soil, which can improve organic matter, soil microbiology, and overall plant health.
Perhaps the most significant lesson in our research project was to "understand your soil before you add anything." There is no 'one-size-fits-all' approach when it comes to soil health. What may work for one grower, may not work for another. The reasons are many and often complex, but there is a growing awareness that understanding the soil’s chemical and biological environment is the key to long-term productivity, resilience, and sustainability. We trust that our research project provides some guidance on this for future research and vineyard operations.
The Future is Bright
This project has demonstrated that insect bioconversion has the potential to make a global impact on how grape marc is managed. While further studies are needed to determine appropriate dosage rates and the full influence of insect frass on vine health and disease resistance, the initial results are incredibly promising. We believe there is convincing evidence to support further in-field trials to validate the benefits to soil and plant health.
With each project, we are building a body of foundational data that will ultimately be used to build a business case that helps wine companies meet their Environmental, Sustainability, and Governance (ESG) goals, not only in Australia but globally. Australia has always been a beacon of innovation in winemaking and viticulture, and many overseas operators look to the Australian industry for new ways of doing things. We have already had conversations with European vineyard operators who have expressed interest in the outcomes of our grape marc conversion research projects and vineyard trials. Hence, there is strong potential for collaborative and joint venture-type investment (across public and private partnerships) to build insect bioconversion facilities in regional areas to close the loop on grape marc.
Join the Sustainable Revolution
This project was made possible with funding from the Penfolds Evermore Fund 2025. For more information on our insect bioconversion technology, please visit our website or contact us directly. Together, we can build a more sustainable future, one black soldier fly at a time.
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