Eat, drink and be chemists

Rice University students are helping a high-profile Houston chef take a scientific approach to making custom vinegars and beverages shrubs. The products are intended to be not only delicious, but also to support local farmers by preserving what they grow.

Chris Shepherd, the James Beard award-winning chef and owner of Houston restaurant Underbelly, has developed an informal partnership with Rice students learning practical chemistry and microbiology while they help his operation refine its approach to turning what would otherwise be wasted produce into useful products.

“We buy as much (produce) as we possibly can, but to do that we have to be able to use it in different ways, and forms of preservation are the oldest way we know how to,” Shepherd said during a recent visit to the class. “(We want to make) sure we’re doing that in the right way.”

He knows a good thing when he sees it. Shepherd, who earned Best Chef Southwest honors from the James Beard Foundation in 2014 – the first Houston winner in 22 years, spent time at Rice in April to hear how students analyzed the fermentation of grapes and pears into vinegar.

The chef and Rice lecturers Sandra Bishnoi and Michelle Gilbertson put students in two classrooms for freshman courses, sciences/” title=”View all articles about Natural Sciences here”>Natural Sciences 120 and honors general chemistry, to work on the problem this semester. Their task was to quantify chemical processes and identify the microbes present in the production of vinegars and, in turn, shrubs (aka drinking vinegars) from produce that can’t be used fresh.

“In order to make shrubs, you have to have vinegar,” Rice student Jessica Hartz explained. “You basically start out with a big tub of fruit; then you pour a ton of sugar and some water into it. You let that sit for a little while so it can kind of juice itself up, and then you add more vinegar to it, and that addition of the vinegar is kind of the catalyst that gets the process started.”

The continued presence of bacteria is key to the fermentation of produce into alcohol, then vinegar, she said.

“We looked at the alcohol, acidity, sugar, all those things,” said classmate Tareck Haykal. “We found out that their vinegars are extremely alcoholic, more than the average wine. If there were bacteria in there, the alcohol should be converted to acetic acid, to be more acidic and less alcoholic.

“We thought, ‘What if there’s no bacteria?’ We learned that was the problem,” he said. “This was a lot more impactful than I would have thought.”

Shepherd and his staff have relied on the age-old techniques of taste, clarity and smell to determine when a batch of vinegar is ready for use, but those don’t scale up. “It’s like throwing darts in the dark,” he said.

“I started to research this after talking to our cocktail bars, where they were just taking a peel of citrus sugar with juice and letting that sit, then adding vinegar; and then they would use that in a cocktail,” Shepherd said. “That seemed like a pretty viable solution to make two quarts. I need to make 20 gallons.”

The restaurant was already monitoring acid levels during fermentation based on previous work with Rice chemist Lesa Tran, a self-professed “foodie” who got Shepherd involved in a “chemistry of cooking” class in 2014. The tricky part that remained was to quantify what happens as produce ferments first into alcohol and then into vinegar, Bishnoi said.

“They thought monitoring the pH was good enough because that would tell them if they were killing bacteria,” she said. “But some of the shrubs were too sweet, according to our taste testers, even though their acid levels were the same. At the end of last semester, we determined that they were doing a good job of controlling the amount of sugar they add, but they weren’t thinking about the innate sugar of the fruit itself.”

The students determined that the acidification part of fermentation releases a surge of sugar from the fruit that can oversweeten the product and found a way to measure it, Bishnoi said.

She said the students also developed a way for the restaurant to monitor the amount of beneficial gram-negative acetic acid bacteria present in vinegar production. In the process, sugar from the fruit first turns to alcohol with the help of yeast, then to acidic vinegar, all under the catalytic influence of bacteria. But if there’s too much alcohol too early in the process, the bacteria die and fermentation stops.

“Getting a consistent vinegar product is very hard,” Bishnoi said. “It’s time-consuming, but the introduction of acid is a great way to reach the goal of preservation. Once you’ve made a consistent vinegar in the restaurant, you now can use that in all of your other preservation methods.”

Gilbertson’s students closed in on the goal near the end of the semester. “The research revealed that the acetic acid required for vinegar’s sharp taste was not present in significant amounts,” she said. “In the last set of experiments, the addition of mother of vinegar, which contains the bacteria required for the conversion of ethanol to acetic acid, successfully increased the total acetic acid to as high as 5 percent in two weeks. Commercial vinegars contain 6 percent total acid.”

She said that may be enough, but the chef’s own taste buds will be the final arbiter. “That would be the first step,” Gilbertson said. “Some of the vinegars had gone to zero percent ethanol, so there would be nothing more to convert.”

The freshmen were grateful for the chance to work on a project with a real-world application. “It might not have been as beneficial for Chef Chris as we luckily had it turn out to be,” Gilbertson said. “Of course, there was a problem to solve in the first place. That’s why they came to us. If the process had been going swimmingly, there would have been no reason for us to look at it.”

Shepherd described working with Rice students as “a highlight in my career.” One result will be the ability to help keep his farmer clients in business. “When I give it back to a farmer that grew something for me and I show them what we’ve done with it, it brings them to tears. Because they know that we did that justice.”

Another result, Haykal noted, is that the chef “learned a lot more than expected.”

“What’s old is new again,” Shepherd said. “We’re doing something that has been lost for a very long time.”

With a twist, thanks to Rice.