Listening for a Strange Brew

Researchers at the Pacific Northwest National Laboratory (PNNL) have devised a way to quickly measure and track the quality of fermenting liquids, such as beer, without having to draw samples from a batch. Sampling fermenting liquids is necessary to ensure quality, but it can be time-consuming and potentially contaminating. By using ultrasonic backscattering, a method of reading sound signals as they bounce off targets and back to a sensor, the PNNL team's system avoids these drawbacks and gives the brewer greater control over the fermenting process.

"This method really shines because it only requires one sensor to sit on the side of a container like an earphone," says Richard A. Pappas, a senior research scientist on the PNNL team. The sensor is a transducer that sends and receives ultrasound information. "We can preserve the container's sterile environment and obtain accurate and continuous information about cell growth and population size over the length of a life cycle."

To employ the team's system, the brewer would first have to run a controlled experiment to calibrate the ultrasound for tracking cell growth and concentration. This requires finding a strong relationship between the changes in a perfect batch as it ages and the changes in the sound strength and frequency as a signal backscatters off that batch's aging microbes. Over its life cycle, each microbe will scatter the ultrasound signal in a characteristic way because, as the microbe grows, it will come to have different mechanical properties. The microbes will vibrate differently depending on how big they are, how much they weigh, and how they are clustered with other particles nearby. Once the sound signature of a flawless fermentation is obtained, that information can then be used to measure and perfect future batches as they ferment.

There are other nonsampling methods to characterize a fermentation process, such as using electromagnetic resonance. But one difficulty these methods face is that their effectiveness depends on the material a container is made out of. Unlike these methods, Pappas says, his team's ultrasound technique is not limited by the container.

The PNNL researchers recently received a patent for their system based on tests that benchmarked the ultrasound's ability to measure concentrations of 35- and 70-micrometer particles in deionized, degassed water. PNNL currently has no time frame for commercializing this technique, but the team looks forward to fine-tuning the system for specific applications, such as brewing beer and creating pharmaceutical slurries.

"For the microbial process world, their method has promise," says Chris Wend, a fermentation specialist at Northwest Agricultural Products, who is familiar with the PNNL work. "But it will require some honing once it's out of the lab and in real-world situations."

One person eager for such an advance is Robert Cannon, a brewer at the Boston Beer Company, owner of Sam Adams. "A real-time, in-line sensor is something I couldn't imagine any brewer not being interested in," Cannon says. Currently, Sam Adams takes samples from a port on the side of a container and then performs daily tests during fermentation. Cannon says that if the PNNL method could help prevent various problems before they mature, such as a hung fermentation or spoil due to various bacteria like lactobacilli, "it would be very useful indeed."

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