Insect meal processing is emerging as a sustainable and efficient solution to meet the growing demand for high-protein products, primarily used as feed for animals like fish, pet food and poultry, and sometimes for human consumption. The larvae stage is often targeted due to its high biomass and nutritional value.
In insect meal production, several types of larvae are commonly used due to their high nutritional value and efficiency in converting organic waste into biomass. The most widely used species is the black soldier fly larvae (Hermetia illucens), known for its ability to thrive on a variety of waste materials, including food scraps and manure. These larvae are rich in protein and fat, making them ideal for animal feed, and their frass is also valued as a fertilizer. Yellow mealworms (Tenebrio molitor) are another popular choice, especially in both animal and human food products. They are typically reared on grain-based substrates and have a high protein content with a lower fat profile compared to black soldier fly larvae. Lesser mealworms (Alphitobius diaperinus), or buffalo worms, are smaller but similarly used in poultry and aquaculture feed. Housefly larvae (Musca domestica) have been used for waste decomposition and feed, though they are less common today due to biosecurity concerns. Lastly, silkworm pupae (Bombyx mori), a by-product of the silk industry, are often utilized in insect meal, particularly for fish feed, owing to their high protein content.
Each species varies in terms of rearing requirements and nutritional composition. This different rearing conditions give rise to different levels of odour potential, ranging from the decaying waste to the final frass to the storage and transportation. Irrespective of the species used for the insect meal production, the processing of insect larvae to the meal always have similar line of odour generation. The decomposition of organic waste, microbial activity, and thermal processing contribute to the emission of volatile organic compounds (VOCs), ammonia, and sulfur-based gases, leading to unpleasant smells. These odours can impact worker comfort, community relations, and environmental compliance. To address these concerns, implementing effective odour control solutions is crucial. Being said that the black soldier fly larvae generally associated with stronger odours due to the nature of their feed substrates and metabolic activity.
This article explores the sources of odour in insect meal processing, the challenges they present, and the most effective strategies for odour mitigation.
Odour is a natural byproduct of organic processing, and insect meal production is no exception. The breakdown of insect biomass, drying processes, and fermentation stages can release volatile organic compounds (VOCs) and other odorants. While these smells might not bother the insects, they can be off-putting to nearby residents or workers. Effective odour management not only ensures compliance with environmental regulations but also fosters good relationships with local communities and supports the industry’s reputation as a sustainable solution.
Insect meal processing is a highly sustainable source of protein, but it presents significant odour challenges. Understanding the sources of these odours is essential for developing effective control strategies. The primary sources of odour in insect meal production stem from raw material decomposition, insect rearing conditions, processing stages, byproduct treatment, and wastewater management.
1. Rearing Phase (Larvae Growth)
This initial stage involves growing insect larvae—such as black soldier flies, mealworms, or houseflies—on organic substrates. The odours emitted during this phase originate from the feed, the larvae themselves, and microbial activity. Feed substrates play a significant role: organic waste like food scraps or manure decomposes, releasing volatile organic compounds (VOCs) such as ammonia, hydrogen sulfide (with its characteristic rotten egg smell), and short-chain fatty acids like butyric acid, which smells like rancid butter. Grain-based feeds, such as wheat bran or oats, can undergo fermentation or fungal growth, producing odours like alcohols (ethanol) and esters that have fruity or solvent-like characteristics.
Larval metabolism contributes further to the odour profile. Frass—the combination of insect excreta and undigested substrate—produces nitrogenous compounds such as ammonia and amines, which smell sharp, fishy, or decayed. In addition, larvae release hydrocarbons through their cuticles, emitting faint waxy or oily odours. The microbial decomposition of feed, whether through aerobic or anaerobic pathways, generates sulfur compounds like mercaptans and additional organic acids, which amplify the odour intensity and complexity during this stage.
2. Harvesting Phase
During harvesting, mature larvae are separated from their substrate, often through mechanical means. This disruption enhances the release of odorous compounds. Residual wet substrate left behind after separation can undergo anaerobic decomposition, producing intensified sulfurous and putrid smells. Handling live larvae may cause stress responses, leading them to release defensive compounds like aldehydes (which have sharp, green odours) or pheromones that are often musky or acrid, depending on the species.
Cleaning processes during harvesting, such as rinsing the larvae with water or solvents, may dilute some of the odours but can also stir up stagnant, earthy smells from organic residue. The combination of biological and mechanical factors in this phase makes it one of the more dynamic contributors to the odour profile in insect meal production.
3. Processing Phase (Conversion to Insect Meal)
This phase includes the killing, drying, and grinding of larvae into meal. Different killing methods impact odour differently: freezing typically emits minimal odour at first, though thawing may release faint protein breakdown smells. In contrast, heat-based methods like blanching or boiling cause Maillard reactions (browning reactions between proteins and sugars), producing more pronounced roasted, nutty, or even meat-like aromas.
Drying, whether via oven or air, concentrates VOCs by evaporating moisture. This can result in toasted, earthy, or slightly burnt odours—especially if overheating occurs, which can create acrid or charred smells. Grinding the dried larvae into meal releases fine particulates, emitting nutty, hay-like scents. However, if the lipids in the larvae oxidize during this process, particularly in fat-rich species like black soldier flies, they can produce aldehydes such as hexanal, which carry rancid or oily smells.
4. Oil Pressing Phase (Lipid Extraction)
In facilities that separate insect oil from the protein meal—especially with species like black soldier flies—mechanical oil pressing introduces additional odour sources. When pressing is done with heat, or when heat is generated from friction, thermal breakdown of lipids can occur. This leads to the formation of aldehydes, ketones, and volatile fatty acids, producing smells ranging from grassy and paint-like to rancid or sour. If pressing temperatures are too high, acrid or burnt-oil odours may develop.
Oxidation of fats during or after pressing is another key contributor to odour. Rancid, stale-oil-like smells can emerge from unsaturated fats breaking down, particularly if the oil is not processed or stored in an oxygen-limited environment. The residual press cake may still contain fat and moisture, contributing warm, earthy, or slightly sour odours if it is not cooled and dried promptly. Emissions may also arise from hot surfaces and oil collectors, especially in enclosed spaces without adequate ventilation, resulting in a lingering oily or meaty atmosphere.
5. Storage and Packaging Phase
Once insect meal is produced, it is stored and packaged, and these post-processing conditions can influence odour stability. Properly stored dry meal usually has a mild, nutty, or toasted grain-like smell. However, if moisture infiltrates the product during storage, it can support mould growth, leading to musty or fungal odours associated with compounds like geosmin.
Packaging materials can also interact with the meal. For example, VOCs from the insect meal can adsorb onto plastic or paper packaging, subtly altering the perceived odour with synthetic or papery notes. While this phase may seem passive, it can significantly affect product perception, especially in high-value feed or food applications.
6. Wastewater Treatment Phase
Water is used at various stages of insect meal processing—for cleaning larvae, blanching, or cleaning equipment—and all of this generates wastewater rich in organic matter. The treatment of this wastewater introduces another significant odour source.
If anaerobic conditions develop in wastewater holding tanks, collection pits, or equalization tanks, foul-smelling gases such as hydrogen sulfide (H₂S), ammonia, and volatile fatty acids are released. H₂S, in particular, contributes a rotten egg odour that is often the most intense and noticeable. In addition, foaming and surfactant-rich wastewater can carry odorous compounds into the air as aerosols, especially during agitation or aeration in treatment tanks.
Further odours can arise from sludge handling—the thickened solids separated from the wastewater—which may emit earthy, septic, or musty odours, particularly if not properly stabilized or rapidly removed. Without adequate aeration or treatment, wastewater components can be a persistent and site-wide source of offensive odours, particularly in warm climates or enclosed processing facilities. If not treated properly, this wastewater can become a significant source of odour pollution.
1. Environmental Concerns
Odorous emissions contribute to air pollution and can negatively impact local ecosystems. VOCs and ammonia released into the atmosphere can react with other pollutants, forming secondary air contaminants.
2. Health Hazards
Workers in insect meal plants may experience respiratory discomfort, nausea, and headaches due to prolonged exposure to odours. Strong odours can also lead to reduced air quality in surrounding areas.
3. Regulatory Compliance
Environmental regulations impose strict limits on odour emissions. Failure to comply with these standards can result in fines, operational restrictions, or shutdowns.
4. Community Complaints & Business Reputation
Foul odours can lead to complaints from nearby residents and businesses, potentially damaging the company’s reputation and straining relations with the local community.
To mitigate odour challenges, insect meal processing facilities can adopt various control measures. Biofilters and scrubbers can be used to capture and neutralize odorous compounds before they are released into the atmosphere. Proper ventilation systems can help reduce indoor odour buildup. Wastewater treatment processes should be implemented to prevent the accumulation of organic waste that leads to odour formation. Additionally, optimizing rearing conditions by maintaining controlled humidity, aeration, and feed quality can help minimize metabolic odours from insect populations.
Implementing a robust odour control strategy is essential to maintaining air quality, regulatory compliance, and operational efficiency in insect meal processing plants. Below are some of the most effective odour mitigation techniques:
Biofilters are an eco-friendly solution that uses microorganisms to break down odorous compounds like volatile organic compounds (VOCs), ammonia, and hydrogen sulfide (H₂S). The process involves passing contaminated air through a biofilter medium (such as compost, peat, or wood chips), where microorganisms degrade odorous compounds into harmless byproducts like carbon dioxide and water.
Scrubbers use liquid chemicals to neutralize odour-causing gases. The two main types include:
Activated carbon filters are ideal for adsorbing VOCs and organic odour compounds. These filters trap odorous molecules within the porous carbon structure, effectively neutralizing them before they are released into the atmosphere. This method is particularly effective in handling residual odours after primary treatment.
Thermal oxidation or combustion-based systems break down odorous gases at high temperatures, converting them into non-odorous byproducts like carbon dioxide and water. Though effective, this method requires high energy consumption and is best suited for large-scale operations.
Real-time odour monitoring technologies such as Oizom (www.oizom.com) help track odour levels and detect problem areas. Implementing automated odour control systems allows plants to adjust treatment processes dynamically based on odour intensity.
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Conclusion
Odour control is a critical aspect of operating a successful insect meal production plant. By understanding the sources of odour and implementing a combination of ventilation, filtration, and waste management strategies, plant operators can minimize odour emissions and create a more pleasant working environment. Additionally, investing in odour control technologies not only improves the quality of life for workers and nearby communities but also enhances the overall sustainability and reputation of the insect meal industry.
As the insect meal industry continues to grow, innovative odour control solutions will play a key role in ensuring its long-term success. By prioritizing odour management, insect meal producers can contribute to a cleaner, greener future for animal feed production.
