How to Measure Alcohol in Non-Alcoholic Beer

If you're making non-alcoholic beer, the number you care about most is probably 0.5%. Everything under that number is fine. Everything over it is a problem. The frustrating part is that measuring 0.5% alcohol is a lot harder than measuring 5% alcohol. The tools most brewers already have were built for normal beer, where being off by half of a percent doesn't matter much. When your entire safety margin is half a percent, suddenly it matters a lot.

My name is Nick. I've spent the last eight years helping kombucha brewers stay under that same 0.5% line. For my PhD, I studied genetics in non-conventional yeast. I'll be upfront that I'm a kombucha guy, not a beer guy. But it's the same line, the same biochemistry, and honestly a lot of the same mistakes. Let's start with where the alcohol comes from.

There are two ways to end up with a non-alcoholic beer. The first is to never make much alcohol in the first place. You can stop fermentation early, brew at low gravity, or use a yeast that can't ferment some of the sugars in wort. Maltose is one of the main sugars in wort, so a yeast that can't eat maltose can produce very little ethanol. The second way is to brew a normal beer and pull the alcohol back out, usually with vacuum distillation or reverse osmosis. Both approaches work, but one may be better for your particular operation.

If you removed the alcohol, your risk is that the equipment left behind more than you think. If you never made much alcohol, your risk is that a lot of fermentable sugar is still sitting in the package.

Think about what a non-alcoholic beer actually is. It's a low-alcohol liquid with water, nutrients, and potentially some fermentable sugar left in it. That's a pretty good place to be a yeast cell. If live yeast makes it into the can alongside something it can eat, fermentation doesn't know that you called the beer finished. It keeps going. I've watched this happen in kombucha for years. You package at 0.3%, it sits on a shelf for a few weeks (yes, the alcohol can even rise when refrigerated), and suddenly you are selling an alcoholic beverage as “non-alcoholic”. The TTB would not be happy.

Dry hopping makes this worse. Hops carry enzymes, and hop material can also bring along microorganisms. Those enzymes can break down some of the larger carbohydrates that yeast normally can't touch. That hands your yeast a fresh meal after you thought fermentation was finished. Brewers call it hop creep. In a normal beer, a little extra fermentation is mostly a quality issue. In a non-alcoholic beer, it can become an alcohol problem. Studies of dry-hopped beer have measured substantial changes in fermentability after hopping, and the amount of extra alcohol you get depends heavily on the beer and the process. I wouldn't take a dry-hopped NA beer from 0.3% to packaging and assume the number is going to stay there just because the tank tested fine.

It helps to remember what you gave up. Alcohol is one of the things that makes beer difficult for microbes to live in. You spent the whole process either removing that alcohol or never making it, so what comes out the other end doesn't have the same protection as your regular beer. There's usually more residual sugar, more available nutrients, and less of the antimicrobial effect you get from alcohol. Your NA beer needs more protection than your flagship IPA, not less.

So how do we actually keep it under the line?

Finish the fermentation before you package. This sounds obvious, and it's the first thing to go when a release date is coming. If fermentable sugar is left and anything is still alive in the tank, you've basically packaged a fermentation vessel. The beer might be 0.3% when you fill the can. That doesn't mean it will still be 0.3% when somebody drinks it.

Get your pH down too. The exact target depends on the beer and the process, but getting below about 4.2 after fermentation gives you a much better safety margin than leaving the beer at a higher pH. Closer to 4.0 is even better from a microbial stability standpoint. Most of the organisms you don't want in there have a harder time as the pH drops. This is one of the things kombucha brewers lean on hardest, and it works here for the same basic reason.

Get rid of the yeast. Yeast cells are roughly 5 μm, and filters in that range are not particularly exotic equipment for a brewery. You don't want a bunch of live yeast sitting in a can with fermentable sugar. If you see yeast settling in the bottom of your packages, that's a pretty good clue that you still have a stability problem to solve.

Pasteurize if you possibly can. Tunnel pasteurization is common in NA beer for a reason. It gives you another way to stop the organisms that made it through the rest of the process. Keep in mind that the thermal process you use for regular beer may not translate directly to an NA product, because you took away one of the things that was helping protect the beer. If pasteurizing isn't an option, sterile filtration is the other road, and your cold chain matters a lot more than it does for your other products.

Think hard about dry hopping. I'm not going to tell a craft brewer to stop dry hopping! But if you're making a hoppy NA beer, that's the batch that needs the most testing, not the least. I'd rather find out that the hops are causing a problem while the beer is still in the tank than find out after a pallet has been sitting warm for six weeks.

Now the measuring, which is where I see some of the most confident mistakes. Most brewers reach for a hydrometer, because it's worked for their entire career. The standard math says your alcohol is the gravity drop multiplied by about 131. A typical hydrometer reads to a thousandth of a gravity point. Put that through the same math and one tick on the scale is worth about 0.13% alcohol.

At 5% beer, being a tick or two off is a rounding error nobody notices. At 0.5%, two ticks is your safety margin. And you're taking two readings, so those errors stack on top of each other. That's all before the bigger problem, which is that gravity was never measuring alcohol in the first place! It measures density. Residual sugar, acids, proteins, and dissolved CO2 all push density around. In a normal beer the alcohol signal is loud enough to hear over that noise. In a non-alcoholic beer it simply isn't.

A refractometer has the same basic problem. It measures how light behaves as it passes through the liquid, not how much ethanol is actually in the liquid. Alcohol changes the reading, and so do all the other dissolved things in your beer. You can correct for some of that if you know what you're doing, but at this alcohol level you're trying to pull a very small number out of a measurement that contains a lot of other information. Neither tool is broken. They're just being asked a question they weren't built to answer.

What works is measuring ethanol directly instead of inferring it from density. A lab running gas chromatography is the gold standard, and if you need a number you can defend to the TTB, that's where I would send the sample. It costs more than checking a hydrometer. It also gives you a much better answer to the question you're actually asking.

The trouble is lab turnaround is never instant, and the batch you're worried about is the one sitting in your tank right now. You need to know what it is today, not three days from now after you've already decided whether to package it. That gap is the entire reason I built my own detector years ago. It strips the alcohol into vapor and reads the vapor, so sugar and acid and carbonation stay behind in the tube instead of skewing the number. I built it for kombucha, and non-alcoholic beer is the same measurement problem wearing a different hat. OK, that's all the self-promotion I'll do.

Whatever you decide to use, test more often than feels necessary. Test the tank. Test again at packaging. Then test a can that has been sitting somewhere warm for a month, because that's the one your customer is actually going to drink. A fresh sample tells you what happened in the brewery. An old warm sample tells you what happened after the brewery stopped controlling it.