Why your favorite cup of tea might be a microbiological risk in space

Space · Published 8 October 2026 Swipe more like this →

In short: Loose-leaf tea is a beloved staple for astronauts, making up 7% of spaceflight food samples. However, the temperature of water on the International Space Station may not be high enough to kill dangerous bacteria, turning a comforting ritual into a potential health hazard.

On Earth, the tea industry operates without strict microbial load standards for loose-leaf varieties. This is because the process relies on the assumption that brewing tea in boiling water (100°C) effectively reduces the presence of microorganisms. However, the thermal environment of the International Space Station (ISS) presents a unique challenge to this safety mechanism. This assumption is based on the fact that boiling water is typically expected to diminish microbial presence. Consequently, the lack of specific regulations for loose-leaf tea on Earth stems from this reliance on heat.

The Potable Water Dispenser (PWD) on the ISS typically delivers hot water at temperatures between 155°F (68°C) and 175°F (79°C). This falls significantly below the recommended safe brewing range of 180°F to 212°F (80°C to 100°C). This temperature gap creates a critical vulnerability when dealing with certain pathogens. This discrepancy is particularly concerning for crew members who rely on specific tea preferences for their mental wellbeing. Such temperature variations mean the water provided by the PWD fails to reach the necessary thermal threshold for safety.

In a study involving chamomile tea bags infected with Bacillus cereus—a spore-forming bacterium capable of causing foodborne illness—researchers found that neither boiling water nor ISS-standard hot water significantly reduced the overall microbial load. In one instance, the bacterium was detected at levels exceeding a known infectious dose. This suggests that the brewing process on the ISS does not effectively mitigate the microbiological risks associated with tea consumption. The research specifically utilised chamomile tea bags to test the resilience of these pathogens. Even when using boiling water, the study observed no significant reduction in the total microbial count.

While NASA's Global Precipitation Measurement (GPM) mission focuses on the Earth's hydrological cycle and the essential role of precipitation in sustaining life, the micro-scale challenges of food safety in space highlight the complexity of managing resources in extreme environments. Understanding these hydrological patterns is vital for predicting weather and climate. Such data helps researchers unravel uncertainties regarding the Earth's climate system.

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