Turning silkworm poop into gourmet tea

Insect droppings, often overlooked as waste, may hold surprising culinary potential. Among these, the by-product of silkworm farming – frass – has a long history of use in traditional teas. This study examined how these natural materials can be transformed into a sustainable and flavourful beverage, blending traditional practices with modern techniques to reveal their potential as gourmet ingredients.

“We discovered that silkworm droppings, when roasted, develop rich flavours ranging from earthy to roasted and tobacco-like. Consumer tests showed broad appeal, particularly in fine-dining settings. By turning waste into a premium product, this study highlights how innovative approaches can redefine the value of overlooked materials and promote sustainability ,” explains Nabila Rodríguez Valerón, an analytical chemist turned gastronomic scientist and PhD from the Basque Culinary Center, San Sebastián, Spain. The project was done in collaboration with Harvard University and the Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kongens Lyngby.

The hidden tradition of insect frass tea

Tea, a beverage enjoyed globally for millennia, is most commonly made from the leaves of Camellia sinensis. However, the term tea extends to numerous plant-based infusions and, intriguingly, includes insect teas made from insect frass (excrement). These unique beverages, although relatively niche, have deep roots in traditional Chinese culture, where insect frass teas are prized for their flavours and purported health benefits.

“Tea has such a broad definition, especially in cultures like China, where traditions often include ingredients that may seem unconventional to Western audiences,” Valerón adds. “Insect frass teas have been enjoyed for centuries, not just for their flavour but also for the belief in their health-promoting properties.”

One of the most famous sources of frass for tea comes from insect larvae that feed on specific plant leaves, such as crab apple or walnut trees. The larvae metabolise these leaves, resulting in frass rich in compounds that enhance the flavour and aroma of the tea. Despite their potential, these teas remain underexplored because of limited consumer acceptance and regulatory challenges outside their regions of origin.

“We started this project by reaching out to a company in Greece that produces silk,” Valerón recalls. “They were surprised that we wanted to use the silkworm waste, since it is typically discarded. After seeing our study, they even realised they could profit from this previously unused sidestream.”

Unlocking gourmet potential in silkworm waste

Inspired by these traditions, this study investigated the potential of using frass from silkworms (Bombyx mori) – larvae that exclusively consume mulberry leaves – to create a novel beverage. Silkworm farming, primarily for silk production, generates large quantities of frass as a by-product. Traditionally discarded or used as fertiliser, silkworm frass represents an untapped resource with significant potential for sustainable upcycling.

“Silkworms eat mulberry leaves almost exclusively, although they can consume a few other types of leaves," Valerón notes. "This consistency means that the process and results are reliable, regardless of location. Mulberry itself is known for its health benefits, which further adds value to the frass as an ingredient.”

Mulberry leaves, long valued in traditional medicine and culinary applications, contain beneficial compounds such as polyphenols and flavonoids. Interestingly, silkworm frass retains some of these compounds while developing unique properties during digestion.

“This presents an exciting opportunity to repurpose a by-product of the silk industry into a high-value culinary ingredient.”

Alchemist, a Michelin-starred fine-dining restaurant in Copenhagen renowned for its experimental approach to gastronomy, served as a key inspiration for the study. Known for reimagining ingredients and challenging traditional culinary norms, Alchemist demonstrated how unconventional materials could be transformed into exclusive dining experiences, reshaping consumer perceptions.

“One thing I learned during my time at Alchemist is that consumer perception changes dramatically when products come from a fine-dining context,” Valerón explains. “For example, with insect protein or unusual sidestreams, many people are resistant at first, but if a high-end restaurant uses it, the story changes completely.”

Understanding the aroma profile

This research aimed to explore how silkworm frass – the waste produced by silkworm larvae – can be turned into a flavourful and sustainable tea. By investigating the aroma and taste and how people respond to it, the study combined ancient practices with modern methods to create an innovative and ecofriendly beverage that helps reduce waste.

Silkworm larvae were raised in controlled conditions and fed mulberry leaves, their main food. As the silkworms ate, they produced frass, which was collected. To prepare this frass for tea, it was roasted at 160°C for varying lengths of time: 0, 30, 40 and 50 minutes. Roasting the frass is important because it changes the chemical structure, improving its flavour and aroma.

“We began by reviewing existing research to understand the best ways to use by-products from the silk production process, especially the digestion of the silkworms. By studying the chemical composition of frass, we saw its potential for cooking, particularly when roasted,” explains Valerón.

To better understand the unique smells and tastes of the tea, researchers used gas chromatography–mass spectrometry. This method helps to identify the chemicals that contribute to the tea’s aroma. They discovered 65 compounds, including aldehydes, esters and pyrazines, that gave the tea its roasted, earthy and tobacco-like smells.

“We worked to reduce the moisture in the tea by adjusting the roasting time and temperature,” Valerón adds. “By applying the Maillard reaction, which happens when food is roasted or browned, we created different aromas. We worked closely with a tea expert at Alchemist to fine-tune the process, ensuring that the flavours matched what consumers would enjoy.”

In simpler terms, roasting the silkworm frass changes its structure, making it taste better and smell more appealing. The study used scientific methods to explore these changes, with the goal of turning a waste product into a delicious and sustainable tea.

Unlocking unique flavours

The sensory evaluation involved a trained panel and consumer tests, focusing on such attributes as aroma, texture and flavour. Participants preferred the 40-minute roasted sample for its balance of roasted and earthy notes. This stage helped to ensure the tea’s appeal while maintaining its innovative and sustainable nature.

“We analysed all aroma compounds and described sensory attributes through data-driven sensory analysis, which involved consumer testing to determine perceived aromas and textures. The goal was to bridge scientific findings with real-world experiences,” Valerón adds.

Fermentation may have played a role in developing the tea’s flavour. If the microorganisms present in the natural fermentation process of the frass generated unique aroma compounds, this could indicate that using biological processes might enhance the culinary potential of materials traditionally considered less desirable.

“One sensory attribute we analysed was texture. This tea had a kind of oily, creamy mouthfeel, which I hypothesised could relate to kokumi γ-glutamyl peptides, which create a sensation known in Japanese gastronomy. Further, if fermentation was involved, it may have influenced the overall complexity of the flavour profile.”

By refining roasting, brewing techniques and fermentation processes, the research bridged scientific analysis with culinary innovation.

“The silkworm frass tea emerged as a sustainable gourmet product, appealing to both consumers and high-end dining establishments because of its unique flavours and environmental potential,” says Valerón.

How roasting transforms silkworm frass

The tastings revealed significant transformations in silkworm frass roasted at specific temperatures. Adjusting roasting durations altered moisture content, pH levels and colour, resulting in a product with enhanced shelf stability and appealing sensory attributes.

“Overall, the samples had strong earthy and roasted flavours, such as roasted corn, grain and popcorn, with tobacco leaves also standing out. Sweeter flavours such as honey and caramel were less noticeable. The lowest-scoring flavours were blossom, lilac flower and a fishy taste,” says Valerón.

Of the 31 attributes evaluated, only five showed significant differences between the samples, including cut hay, fresh hay, brown herbal aftertaste, lilac flower and fishy sardine, ranking from highest to lowest score. Notably, except for the fishy sardine note, all of these attributes have been previously detected in mulberry leaves.

“Overall, the tea had prominent earthy and roasted notes, such as roasted corn and popcorn, with less noticeable honey and caramel. The fishy sardine flavour, found in mulberry leaves, was one we had to eliminate – no one wants to drink fish tea. We worked to remove that flavour, ensuring a more appealing and refined taste,” says Valerón.

Exclusive tea’s unique flavour wins over fine diners

The results show that these types of products might have potential.

“For example, the silk production company realised that they could make money from what they previously discarded. This opens possibilities for using large-scale sidestreams,” Valerón notes.

This complexity made the tea suitable for high-end culinary contexts. Feedback consistently pointed to the tea’s unique combination of aroma, texture and taste, suggesting its potential to be embraced as a sustainable and exclusive beverage.

“When people perceive a product as exclusive, they are more likely to try it at least once. If it tastes good, they are likely to continue buying it, even if it originates from unconventional sources.”

The collaboration with chefs and sommeliers revealed how precision in roasting and brewing could unlock new dimensions of flavour. Fine-tuning these variables not only optimised the product but also enhanced its desirability for niche and premium markets.

“For us, the focus was on using new methods in the restaurant. This research was not about comparing the tea to regular teas but about optimising time and temperature for the best sensory outcomes in a fine-dining context.”

Turning waste into gourmet

These findings underscore the untapped potential of agricultural by-products. By applying innovative techniques to traditionally discarded materials, the study demonstrated the feasibility of transforming waste into gourmet products that appeal to both taste and sustainability.

“The potential of sidestreams is enormous, especially considering that manufacturers discard tonnes of material that can be repurposed for consumer products. This study is proof of concept for wider applications.”

This study opens new avenues for integrating sustainability into gastronomy. By repurposing silkworm frass, a silk industry by-product, it demonstrates how waste can be transformed into valuable and desirable products. This aligns with global efforts to reduce food waste and create innovative culinary experiences.

“Sidestreams, often treated as waste, have immense potential. By showing their value, we can transform industries and shift perspectives on sustainability,” Valerón explains.

Redefining fine dining

The findings highlight the broader implications of upcycling by-products, particularly in redefining perceptions of unconventional ingredients. Silkworm frass tea, with its rich aroma and flavour profile, showcases how storytelling and fine-dining applications can overcome cultural resistance and elevate waste into luxury.

“Fine dining offers a unique platform to introduce unconventional ingredients. When framed as exclusive or innovative, it opens the door for people to try what they might otherwise reject,” Valerón notes.

This research emphasises the importance of collaboration across disciplines. Scientists, chefs and industry stakeholders can collectively create groundbreaking products that bridge tradition, sustainability and modern gastronomy.

By demonstrating the sensory and cultural potential of silkworm frass tea, this study provides a blueprint for transforming waste into products that enrich the culinary world while addressing environmental challenges.