I have a new beer rule. Avoid beer in green bottles. Just to be clear, this is a rule for myself. You can drink green bottled beer. In fact, you should always try to drink the beer that you like. For me, I will avoid the green bottles. Why? If you drink beer, you may know why. The the beer in these green bottles seem to have this extra taste that maybe is not so great.

Someone (it was probably my biochemist beer brewing brother) told me that the green bottles don't block ultraviolet light. It is a reaction with the ultraviolet light that causes this taste that I don't like. Well, maybe I don't always trust my brother (even though when it comes to beer, I should). You know what happens next, right? Experiment time.

A Simple Beer-Bottle Experiment ——————————-

Let's start with something that just about anyone could do. Here are my materials. (I actually hate when a lab report lists materials - so I don't know why I am doing it.)

Beer bottles of different colors. Preferably at least one of green, brown and clear. Oh, you will have to remove the beer from the bottles. Maybe you could figure out a way to accomplish this task.

Ultraviolet light. If you don't have one, you could use the Sun. I used one of these UV LED lights.

Ultraviolet sensitive beads. These are little plastic beads that change color when exposed to UV light.

Paper. A flat surface. A notebook. A pencil. A stopwatch. A computer with internet access. A camera.

OK, the experiment is pretty simple. Put some beads in each bottle and let the light shine through. If the beads change color, the UV light passes through the bottle. Simple, right?

Here is what that looks like. Oh, I had cut off the bottom of my bottles in order to use them in another experiment.

Maybe this picture didn't turn out as well as I liked. All of these UV beads start off as white and then change colors when exposed. In this picture, one of the green bottles just had one yellow turning bead under it. Not sure why. But you can clearly see that the beads under the brown glass bottles didn't change colors. Oh, beads in the plastic bag also turned colors. So, from this experiment brown glass bottles block UV light but green and clear do not.

Yes. It's a simple experiment. It would be the start of a great middle-school science fair project if it weren't for the beer.

A More Complicated Experiment —————————–

That is kind of a lie. This isn't really more complicated, it just uses more complicated equipment. In this case, I am using a UV-Visible Spectrometer. Ours looks almost identical to this one on Wikipedia.

A UV-Vis spectrometer basically shines near visible light at a target and measures the amount of light that passes through for different wavelengths of light. The machine actually plots the absorbance (A) for each wavelength where A is defined as:

Where I is the transmitted intensity of light and I 0 is the intensity of the incident light.

Before I show you the data, I just want to point out one other thing. The UV-Vis spectrometer that I used is old. The computer with the software to run it has Windows 95 on it and is not connected to the internet. I had to save my files to a 3.5-inch floppy disk and then find another computer that had both internet access and a floppy drive.

And here is the data. I used python to make the plot look nicer than what it was in the original program. Oh, a quick note. The Becks here is some Becks in a very dark bottle. It was quite tasty.

You can see that for both of my brown bottle samples, the absorbance jumped up near 10. What does this mean? Let's start with the definition of absorbance and solve for the ratio of transmitted light.

So, an absorbance of 10 would mean that basically no light is getting through the glass. I'm not sure why the curve jumps around in that region, but even an absorbance of 4 means essentially no light of that wavelength gets through. Also, we typically say that wavelengths smaller than 400 nm are "ultraviolet." So, for the brown glass, it block out more than just ultraviolet light.

What about the clear glass and the green glass? Well, the clear is very clear. The absorbance doesn't increase until it gets to a wavelength lower than 350 nm. The green glass bottles are fairly similar. They block some light around the 450 nm range and they block some of the larger wavelengths. The point is that both the green and the clear let UV light transmit to the beer.

OK, this clearly isn't a perfect experiment. I'm pretty sure the UV-vis spectrometer wasn't really designed with beer glass in mind. There might be some scattering or reflections going on inside the machine that make the readings not completely valid. However, it seems clear that the green and clear glasses let more UV through than brown glass.

Some Biochemistry —————–

I was confused. Most of these green-bottle beers have a similar taste. But what about clear glass beer? Newcastle doesn't taste like this? What about Bud Select 55? I am not ashamed to say that I also drink that beer. It is perfect for tailgating at a football game or sitting by the pool. But it doesn't have that same taste of a green-bottle beer.

Here is my brother's reply to this question (Eric Allain):

"Certain light sensitive compounds present in hops are the culprit of the skunky aroma which lead to the production of 3-methyl-2-butene-1-thiol (MBT). MBT has an extremely low flavor threshold and is very similar to the compound produced by skunks for defense. Amber bottles block much of the wavelengths of light (~300-500nm) that lead to this photoxidation but green and clear bottles do not. Corona IS skunky ... this is why they serve it often with a lime to mask the smell. Also, the 'skunkiness' has become accepted in Corona as just part of the flavor. Some of the macrobrew companies (Miller-Coors etc) use a hop extract that has been stabilized so that light will not lead to MBT production. Therefore they can use clear bottles without worry. Since the MBT is derived from hop components, different beers with different amounts or types of hops may lead to varying levels of light induced MBT. Boosh!"

OK, some people also claim that the problem is transport and storage. Green-bottle beer doesn't taste bad when it is first bottled. It is just that it has been exposed to UV light for too long. Maybe it wasn't meant to be stored for as long as it is. But what do I know? I'm a drinker, not a brewer.

One last picture. Here is how Samuel Adams sells their six-pack.

I guess they are serious about UV protection for their beer. Not only do they use brown glass, the make the cardboard container with high sides.

Let me send a Hat Tip out to Eric Booth for his assistance with the operation of UV-Vis Spectrometer. Thanks.