Interview: Silicone Bag Brewing
This is a follow-up to the recent post about the study by the students and faculty the department of chemistry at Shippensburg University. The lead authors are Professors John Richardson and Jeb Kegerreis. They spoke with Booch News about the background and implications of their experiments suggesting that brewing kombucha in air-permeable silicone bags optimizes oxygen exposure, resulting in more efficient acid production, lower ethanol concentrations, and greater sugar utilization than kombucha brewed in jars.
Edited transcript (original audio at the bottom).
Booch News: This call was motivated by the fantastic paper you wrote Optimizing Oxygen Exposure during Kombucha Brewing Using Air-Permeable Silicone Bags. I posted a summary of that, created with the AI tool NotebookLM.I’m not a scientist and you guys being analytic chemists, professors at Shippensburg University, you went into a lot of science. I think the net of it was–at the end of the paper where it says Discussion–that you believe that because of a combination of factors, these air-permeable silicone bags are a great way of brewing kombucha and making starter liquid. What led you to choose a silicone bag as an experiment?
The origins of silicone bag brewing
John Richardson: That’s actually a good question. The one thing we do want to sort of clear up here right away is that it wasn’t originally our idea. This was actually brought to us by a fellow brewer out of Joplin, Missouri, a lady by the name of Kimberly Welch, who had a company called Creature Craft Soda. I did a little research, and it looks like they went out of business a short time ago, unfortunately. But she had been brewing in these silicone bags. There’s actually a video from 2022 that you can go back and see. That’s probably the first reference ever to using a silicone bag.
She contacted Cultured Analysis because she thought some interesting things were happening with the bag brewing. She noticed a lot of acidity. Because of that, she suggested that there may be a decrease in the alcohol levels in the bag brews. She wanted us to investigate that for her. She began sending us some samples of some of her finished brews. We noticed exactly that–very high acid content and very low alcohol content in comparison to what we would expect for a comparable brew to be done in a normal jar or other type of brewing vessel. Really, she was the first person to recognize that this could actually be a thing.
We glommed on to it because we were very interested in studying aeration or oxygenation of kombucha brews. We wanted to do it quiescently. We didn’t want to disturb the brew by, for example, bubbling oxygen through it. Using the silicone bag was a very good way of letting the brew essentially soak up the oxygen without having to disturb it. It was an excellent vehicle for studying aeration of kombucha without disturbing the brew.
Initial experiments
BN: So how long was that experiment conducted for? Prior to publishing, the paper in the summer, right? How long was the process that you did in the lab there?
Jeb Kegerreis: What led to the paper were two main year-long undergraduate research projects. When Kim came to us, she said that she really wanted scientific verification of those things that she thought were happening. We explained how our undergraduate research program worked to her. She was gracious enough to let us take that as essentially a system that we can study with our undergraduates. We did two main brewing projects where we had a comparable jar and a silicone bag. We were able to monitor the metrics of each and see what the major differences were. That’s what led to the paper. We’re even continuing that work now. We’re trying to keep brewing, again, bag versus jar-type stuff to see what the differences are, but now we’re changing food sources and things like that.
Silicone bag capacity
BN: Okay. I did have to verify with you when I published that summary on Booch News, which people can find on the October 31st posting, because you’ve given the name of the source of the bags– a company in San Francisco called Anova Culinary Precision. They made a big point of the fact that their bags were airtight, to store salmon cuts and things. Then you confirmed that was the bag you used, and the silicone is air permeable, even though that obviously wasn’t the selling point of the bag. So, my first question is, you do mention in the paper how you brewed three liters of kombucha, but how much is that bag that you purchased? How much liquid does each bag hold? It’s not a three-liter bag, is it?
John: Well, I think it’d probably be a gallon bag. They’re actually advertised as half-gallon bags, but you can easily stuff a gallon of liquid into one. Every bag is just close to a gallon.
Commercial potential
BN: Okay. Now this paper’s just come out. You mentioned the lady who’d been using a system for a couple of years. Has there been any uptake? Are you aware of commercial companies switching to this? Or is this pretty much a laboratory experiment at the moment?
Jeb: We’ve brought it to a brewer here or there on the commercial side of things, but I don’t know that they’ve really enacted it en masse yet. We see it as something that we think will be a useful tool for brewers in the future on a commercial scale, just because it’s a really good system for brewing starter. It just, the acidity and the low alcohol in a short timeframe, it just makes it a really, really advantageous situation for somebody who wants a lot of starter, to be able to then go brew a bunch of commercial brewers with.
Home brewing
John: I just made a brew myself using the bag just the other day and harvested it and then enjoyed it myself, but I just made a gallon. It’s great for home brewing, I think. At this point, if a home brewer wanted to play around with one of these things, it would be a really simple way to get into the kombucha brewing game if you wanted to do that. I think it would be harder on the commercial scale at this point because, first, we haven’t really in any way, shape, or form studied the scale-up process. Obviously, you would have to make a larger bag-equivalent vessel that did the same sort of thing. Then you’d have to study it because the dynamics would be different.
So right now, if you want to make starter in, let’s say, gallon quantities, it’s a really great way of doing that. But what if you wanted to make starter in 30-gallon quantities? Well, that might be a lot harder, or at least something that would have to be investigated and figured out.
Jeb: You could theoretically buy a bunch of bags and have multiple brews going at one time. Because the volume of starter that you need is generally a lot smaller than what you need for your main brew. That’s why we still think that there is a commercial aspect.
But as John said, a part of our research in the future is going to be sort of looking for alternatives that exhibit the same sort of air permeability but can hold more volume.
Leach proof?
BN: Well, one question that came up on the Instagram post that I put up, a couple of people immediately posted comments, raising the question that most kombucha manuals or the instruction books for home brewers and commercial brewers recommend ceramic containers, which is what I use. Then there’s obviously a whole market of stainless steel vessels that are used in craft beer as well, of various sizes, up to many thousands of liters for the larger brewers. The question was, is it healthy or is there a risk of contamination of the silicone plastic leaching into an acidic liquid? I don’t know if your lab can analyze the chemistry of that. What’s your thoughts on that?
John: Well, one thing that we know, is that silicone is a polymeric material like plastics. One thing that’s known about silicone is that it’s highly chemically inert, even compared to a lot of other plastics, and has to do with the nature of the polymer backbone that makes it up. One thing that you see with silicone is that if you look at its chemical structure, it’s really a chain of atoms, right? That chain consists of alternating silicone and oxygen atoms.
In that sense, it’s very close to glass. Glass is essentially polymer like that, also made up of silicone and oxygen. It’s closer in terms of its chemical structure. It’s more similar to glass than it is to the typical hydrocarbon-based polymers that people talk about. One example is that people use it for all sorts of things. It’s been used for many, many years for breast implants–also silicone. People don’t seem to mind putting it in their bodies and leaving it there for long periods of time. That’s one consideration. The other thing also is that it doesn’t have a copolymer agent such as BPA, which people talk about a lot. When you process silicone, there’s no BPA or any other copolymer additive like that that could then leach out, like, for example, you hear about in polycarbonate water bottles.
Jeb: Our organic chemist brought up another point, too, because we brought this to him because he has a lot more knowledge in that side of things. A lot of cookware is silicone coated. It’s out there as a usable semi-nerd material that is used in the food industry, obviously, and other industries as well.
Now, to be fair and to be like a scientist about this, we haven’t studied it directly, right? So kombucha does have a different sort of chemical makeup with low pHs and things like that, where it would be something in the future where if this took off, that it would be worth looking into. But from the standpoint of just the knowledge that we have and then the experts that we talk to, it looks like it would be a really good situation to avoid some of the issues with microplastics and things like that.
BN: Yeah, that’s interesting because, not being a scientist, you’ve just explained the sort of chemical makeup of silicone. It’s not like all plastics are the same. What you’re saying is it’s more like glass. How would it compare to, for instance, there’s one brand called Captain Kombucha in Europe, sold in plastic bottles. There’s also the lining of the aluminum cans. I know he’s advertised as BPA-free these days. Is that silicone as well, or is a plastic bottle a different kind of plastic or a different kind of substance?
John: Based on what I’ve seen with that sort of thing, I believe it’s a different kind of polymer. It’s also plastic-based. But again, the same concerns are there.
When you think about, for example, a polymer or plastic-coated can, they all have that. That’s so the aluminum doesn’t degrade under acidic conditions and you get aluminum in your kombucha. The idea there is no matter what you put your kombucha in contact with, there’s always going to be some leaching. There’s always going to be something that’s going to make its way into the kombucha in very, very tiny quantities.
Even if, for example, in a stainless steel fermenter, it’s probably going to have a fairly robust oxide layer on it that protects it. But there’s still going to be stuff leaching out of even something like stainless steel that’s going to go into the kombucha. In that sense, it’s a problem you’re never going to 100% avoid. It’s just a problem that you’re going to be able to mitigate.
There’s really very little difference. If you think about that, somebody who is putting a kombucha, for example, in a plastic bottle or a plastic lined can, that’s really not that different than leaving a kombucha to brew for a week in a silicone bag when you really think about it. I mean, it’s much less time.
Maximum oxygenation
BN: Yeah, your brewing process takes a week, whereas it can be on the store shelves the expiration date can be a year in the future. This idea which your paper explains in great detail–about the advantage of extra oxygenation–how this overall gas permeable surface area of the bag far exceeds that of a jar of equal volume. I do know you’re probably aware of one of the manufacturers out there called Stout Tanks. They make a very flat, almost bathtub-shaped brewing vessel, They advertise it as it has much more surface area. Even if people don’t use plastic bags, your experiments point to the fact that maximizing the surface area is a good thing.
Jeb: Exactly. It’s very much akin to that. It’s all about just making sure that as much of your kombucha as possible is open to the atmosphere where the auctions contain. Stout Tanks trays are doing exactly the same sort of thing. The nice thing about the bag is that you have 360 degrees to play with. It’s just completely encapsulating your volume so you kind of there’s this thing called an interfacial area if you want to get fancy with it. But essentially like the surface area to volume. It really takes advantage of it to a great extent by usage of the bag.
SCOBYs
BN: I’m aware as all home brewers are–you see it all over the Facebook groups for home brewing–of what is a SCOBY? Originally people thought the SCOBY was the pellicle and now everybody is much more aware that the symbiotic culture bacteria and yeast is the starter liquid and the pellicle is a byproduct. So, you can actually brew kombucha absent the pellicle if you’ve got sufficient starter liquid. But your paper says that another consideration is the enhanced formation of pellicles throughout the inner surface area of the bag. Are you saying when you put a gallon of the liquid in the bag that you get a pellicle–that well known gelatinous substance–across the whole surface of the bag?
Jeb: You’re going to grow a bag within the bag. Eventually a pellicle completely surrounds your kombucha. The SCOBY is definitely in the liquid, but the pellicles are an important part of that too. because we think it provides protection for the microbes that are part of the SCOBY.
Along the entire surface of the bag it starts as a thin layer and then eventually as time goes by just like your pellicle on the jar, it’ll thicken up. Then eventually you could even just sort of remove the pellicle as a whole from the silicone bag and it can just, it’s, it’s sturdy enough to suspend the kombucha within it.
John: It looks like a pillow almost when you pull it out of it.
BN: Does that limit the amount of oxygen if you have a thicker pellicle you’re not getting as much air into the liquid itself?
Jeb: I think it’s a really good question. We tried to look into this. Again, it’s one of these things that is on our list of future research to do. But certainly from the beginning, and over the short timeframe that we’ve used the bag to brew starter, the maximized oxygen exposure is definitely beneficial.
It’s a really good question to ask: is there maximum exposure up front and then at the end it restricts it? Does that then speak to different processes happening towards the end of the brew that wouldn’t be necessarily as prevalent in the front of the brew? But to answer your question directly, no, we haven’t really looked into that yet.
We just know that when we look at the dynamics of the processes of the microbes that they’re, they’re certainly enhanced in the bag versus an equivalent jar.
John: We’ve run some of these experiments for upwards of 30 days. So you’re generating pretty thick, pellicle in 30 days. Yet we still seem to notice the effect of greater oxygenation even across the entirety of that brew time.
Cultured Analysis update
BN: Well, this is great. I’d like to just have you bring me up to date on the developments for you at the Shippensburg University Analytic Chemistry Lab and Cultured Analysis which people should listen to the first podcast from July 23, 2023.
I looked at your Instagram. It seems you had some very keen undergrads or graduate students, Cole Pearson, Lizzie and Abby, who are part of what you call a “Brew Crew”—a part of Cultured Analysis. So, you have commercial clients and the undergrads step in and run experiments. But how’s, how’s Cultured Analysis doing since we spoke last 18 months ago?
John: Well, we’re doing okay. We’re holding our own. We’re getting more and more clients over time, which is a good thing. It’s just like any other small business though it kind of ebbs and flows. August and September, I was so busy. I didn’t know what to do with myself. Then in October, November business has kind of fallen off. But that’s kind of the way it’s been. It ebbs and flows. But the nice thing about it is, we’re sort of in here. I like to think of it almost as a symbiotic arrangement because we’re in a university. When business falls off a little bit, there’s all these experiments to go do.
There’s brewing to be done, there are students to be engaged. It just turns out there’s always plenty to do. The neat thing about it is when we think about Shippensburg University’s Chemistry Department and Cultured Analysis, we’re kind of one and the same. The students don’t necessarily get directly involved in my work with clients, but we’ve got all this research going on, on the side the students involve themselves with.
We’ve introduced kombucha brewing and analysis into the curriculum here. We’ve got entire laboratories across the semester that are geared to understanding the brewing process and how to make measurements. We’ve got students brewing. That’s the Brew Crew. So, they’re involved. It’s really cool to see because they get to decide, okay, what vessels are we going to use? What teas are we going to use? How are we going to flavor the kombucha? When do we call it done? When do we harvest it? So, I mean, they do the whole thing, which is really, really neat. It really involves them in a very unique sort of way.
Student success
Jeb: Cultured Analysis interfaces with the university really well. We essentially have students that are freshmen to junior year where they kind of address a little bit of interest in kombucha and we involve them in the brewing. It’s more of a fun thing, like when a brewer would do at home. Then for senior research for our undergrads, it gets a little bit more formal and stringent. That’s when we can really dig into a lot of these problems that become the focus of our research. We’ve had really good success with our undergrads. We’ve even been featured by the American Chemical Society. They did a whole media write-up about our research group last year.
And even our students now, we have two current students working on a bag versus jar project where we’re trying to use fructose as a food source.
And they’ve even won a travel award to the national American Chemical Society meeting. The company really brings a real nice advantage to the students that we have in terms of giving them opportunities to do real world like impactful research on kombucha.
John: The stuff that we learn through the research that we do with our students, yes, folds directly back into the knowledge base that Jeb and I have to work with our clients in terms of consulting and R&D and this kind of stuff.
Jeb: I would say we’re picking up, we’re picking up a little bit more consulting work and having these tools and this knowledge in our back pocket to be able to apply to other people’s problems really is a benefit for the company.
BN: Have you had any graduates go off into the industry, either starting their own kombucha company or working with others around the country that you’re aware of?
John: Not yet, but they’d be stealing our thunder, I’m afraid. It could happen!
BN: Well, I did hear one lady say that she now brews kombucha at home. Some of them are motivated not just to come in the lab and run it through test tubes, but enjoy the benefits of being able to drink kombucha at home.
John: Yeah, a couple of ours dol Lizzie does brewing at home.
Jeb: Kombucha for us from the standpoint of the university is an amazing vehicle to get into real-world chemistry. A lot of our graduates go off to graduate school and they’ll be doing work in analytical chemistry or maybe biochemistry. Things that they’ve picked up on and got an experience with kombucha. Now they’re going on and get into the bigger field as a whole based off of that as a launching pad.
Biochemistry
BN: Do you do any, there is an organization I connected with in Oakland that does kind of citizen science. They run a program using begged, borrowed, and stolen equipment–well, maybe not stolen–but they have a lab they built and they go as far as doing DNA analysis. Have you taken it as far as DNA or is that more biology and chemistry?
Jeb: No, we’re still in like focused on the chemical components and then obviously the biochemistry is a big important part of that, but we really are focused in on like what like the main chemical components are for a brew and tracking them over time.Most of our research and our consulting work is focused around that.
John: I mean, the biological side is something that would be really nice to learn.
But first of all, it’s really not our specialty. Jeb and I will agree on one thing. We tried to avoid as much biology in college as we possibly could.
Looking back on it was probably a bad idea.
John: We want to think of ourselves as pure chemists, but then when you get into the real world like this, you realize that biology and chemistry are very, very much intertwined. You can’t really have one without the other.
Jeb: In fact, a lot of the arguments we make in the paper and in our current research are sort of inferring what must be happening with the biology based off the chemical results that we see. Future projects will have to dig in and make sure that our hypotheses are correct with those respects.
John: That’s what I like to say about the chemistry of kombucha, especially as Jeb mentioned when you’re looking at it as a function of time. What it’s telling us is basically what those microbes are doing. We do get some insight about who the microbes are and what those microbes are doing by looking at the chemicals that they generate those microbes are little chemical factories. That’s what I like to tell our students.
BN: Well, guys, it’s been great to catch up with you and get clarity on the experiments you’ve done using air-permeable silicone bags and wish you every luck developing that.
John: Well, thank you, Ian. It’s always good to come on your podcast. We always enjoy it.
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