Hot Bottles, Honest Answers: How We Tested the Heat Stability of ZBiotics Pre-Alcohol

At ZBiotics, answering customer questions using the scientific method is in our DNA. So, when summer arrived and customers began asking what happens when ZBiotics Pre-Alcohol gets hot—whether in a mailbox, a backpack, or a glovebox—we knew we had to find out for sure.

Is a bottle still functional after a few hours in the sun? What about multiple days of heat during shipping? Rather than speculate, we did what any good scientist would do: ran experiments to get real data.

The question: what happens when Pre-Alcohol gets hot?

With summer in full swing, our Customer Care team has been receiving more questions about how heat affects ZBiotics Pre-Alcohol bottles. So we checked in with Jaime N., our Ecommerce Customer Experience Manager, who hears from many of you directly. According to Jaime, “Once summer hits and people are heading to BBQs or traveling, we start getting these questions regularly—at least five a week. Everyone wants to know how hot the bottles can get and whether they’re still good.”

Here are some examples of the questions we get:

• “My package sat on a sunny porch all afternoon—will the bottle still work?”
• “I left it in my car during a music festival. Is it still good?”
• And a more extreme heat scenario: “My latest box came while I was out, and I couldn’t grab it until just now. The delivery person placed it on a radiator, and the box was hot to the touch. Do you think the bottles are heat-damaged?”

While we're confident in the hardiness of our bacteria (we specifically designed the product starting with the endospore-forming B. subtilis—more on that in a second), these are valid concerns—and we realized it was time to collect data we could share with our customers. After all, we’re scientists!

ZBiotics Pre-Alcohol contains a live probiotic, genetically engineered to help your body break down acetaldehyde. The species we use—Bacillus subtilis—is particularly robust thanks to its ability to form endospores. These endospores allow the bacteria to survive extreme environments, including the low pH of the stomach and temperature fluctuations. That’s what enables us to deliver a shelf-stable probiotic that can also make it safely through your digestive system. We chose to start with B. subtilis in part for this reason, because it’s so robust and thus most likely to remain viable between our warehouse and your gut!

But like any living thing, even our tough little probiotic has its limits—especially when it comes to heat. And while there is a lot of scientific literature on the ability of the bacteria itself to survive very high heat, it’s also important for us to understand how our endospores tolerate it once they’re in our formulation. So the question is: what actually happens when a bottle of Pre-Alcohol gets hot, and how hot is too hot?

The experiment: simulating real-world and extreme heat

We worked with our Director of Research and Development, Kim W., PhD, to design an experiment that tested how ZBiotics Pre-Alcohol holds up under both typical summer conditions and extreme heat—giving us a complete picture of the product’s stability.

What we did

We exposed bottles to six different temperatures—each chosen to reflect the kinds of thermal stress they might realistically encounter, whether you’re bringing them along or accidentally leaving them behind.

At each temperature, we stored three bottles for 4, 8, 24, and 48 hours. After each time point, we measured how many of the probiotic bacteria survived by counting how many bacterial colonies grew on a petri dish per milliliter of Pre-Alcohol (CFU/mL) and compared it to bottles that we didn’t expose to heat. From there we could calculate what percentage of the bacteria remained “viable” in their ability to grow and reproduce (percent viable).

What we found

The results were clear:

• 21°C / 70°F: Baseline control, completely stable
• 37°C / 98.6°F: Completely stable
• 43°C / 109.4°F: Minor losses only after long exposure (48 hours)
• 50°C / 122°F: Larger decline, ~50% of the probiotic viable after 24 hours
• 70°C / 158°F and above: Near-total loss of viable probiotic

As you can see above, temperatures up to 43°C (109.4°F) are generally well-tolerated—even after 48 hours. That’s hot (imagine standing outside on a 110°F day!), but the probiotic holds up surprisingly well. However, things change quickly at 50°C (122°F). Degradation begins within just a few hours: we observed about a 15% loss in viability after 4 hours, and by 24 hours, a little over 50% of the probiotic remained. In general, if the bottle feels very hot to the touch, that’s a good sign it may have been exposed to degrading temperatures. And if you leave the product on your radiator, it’s going to decline pretty quickly.

To put this in real-world terms: research shows that the dashboard of a car parked in direct sun can reach an average of 157°F (69.4°C) on a hot day (Vanos et al., 2018)—a temperature that would essentially “cook” the contents of your Pre-Alcohol bottle. By comparison, in the shade, a car’s dashboard averages around 118°F (48°C), and the rest of the car is usually a bit cooler, around 105°F (40.5°C). So while you should definitely avoid leaving your bottle on a sunlit dashboard, tucking it away in a shaded glovebox for a few hours is likely just fine.

Another useful clue? Check the tamper-evident seal. If it looks cloudy, the bottle likely experienced extreme heat. Many of these seals are made from PVC, which turns from translucent to opaque around 70°C (158°F). In our testing, bottles exposed to 70°C (158°F) and 90°C (194°F) consistently showed this clouding effect—right in line with the point at which we saw complete loss of probiotic viability (note: this visual cue applies to our current packaging and may change if the seal material is updated.)

Our conclusion: treat your Pre-Alcohol like a microscopic pet

The probiotic in ZBiotics Pre-Alcohol doesn’t need refrigeration, but it is a living organism. And while it’s shelf-stable even in relatively warm conditions, extreme heat can eventually kill it.

So, here’s our best advice:

• Don't store your Pre-Alcohol bottles in a hot car.
• Don’t let them sit in direct sunlight for extended periods of time.
• Don’t leave them on a radiator or other direct heat source.
• If the bottles feel hot or the seal looks cloudy, reach out to our Customer Care team.

“Definitely reach out if there are concerns. It’s better to ask. We’ll always take care of you! As with any science-related question that comes in, we do actually consult the scientists before we respond to make sure you get the most up-to-date information from us.” -Jaime N.

Why we did this

We didn’t conduct these experiments because we had to. We did it because customers asked a great question, and while we had some good hypotheses based on the available literature, we believe in responding with specific data from well-designed experiments.To do that, we turned to our Director of R&D, Kim, who summed up the experience here:

“It's always a challenge to make the well-controlled, highly reproducible experiments we do in a lab directly relevant to the messy real world we all actually live in. But I think we did a good job of finding conditions we could create in the lab that can be directly applied to common questions like, “How long can a bottle sit in the sun?” or “Can I store Pre-Alcohol in my car?””

Our job doesn’t end when a product leaves our lab. It continues with every question, every data point, and every opportunity to make the experience better. That’s what we mean when we say we’re science-first: it’s about answering with evidence, building with intention, and always striving to do better.

Thanks for your questions. Keep them coming, and we’ll keep answering.