experiment

Photo, from L-R: Le Chouffe, Flying Dog, Weistephan 330 mL and Orval bottles lined up after weighing.

In all my years of homebrewing, I’ve never worried about bottle bombs, i.e. when a bottle of carbonated home-brewed beer explodes, though in all those years I’ve always aged my beer and bottled to a standard 2.5 volumes of CO2. This time, however, I may be pushing the pressure limits of the standard US 12-ounce bottle.

My current beer, which I plan to bottle condition, is a German hefeweizen. Bottling it in the traditional way calls for 3.3-4.5 volumes of CO2. The effervescence and yeast that settles in the bottom of the bottle are hallmarks of this style, characteristics which I would lose were I to keg. Popping the bottle then releases the pent-up carbonation, forcing the yeast and its distinctive flavor back into suspension.

In true German style, I want to be cautious and methodical about bottling this beer. Unfortunately, there is little to no rigorous information out there about bottle strength, i.e. how much pressure a bottle will hold before it explodes. In the name of science, I’ve collected some of what I’ve found.

Bottle bombs, why?

Anecdotally, bottle bombs happen. Here are several possible culprits:

• Bottling before fermentation is complete;
• Stuck fermentation restarts as weather warms up;
• Infection from bacteria;
• Newbie beer priming accident, i.e. adding sugar directly to bottles, adding too much, not dissolving sugar into warm water first;
• Flaws in glass, especially with lightweight non-returnable bottles;
• Too much priming sugar for strength of vessel.

With temperature control, patience, sanitation, and proper measurement, you may be able to eliminate most of these hazards. The last two hazards, however, require a more cautious approach to selecting bottles.

German engineering

In Germany, and in Belgium, beers are often carbonated in the bottle, and the bottle returned and reused when empty. They are sturdier than the average bottle since they must stand up to both pressure and multiple uses. For these reasons, many foreign beers, even at smaller sizes, have heavier bottles.

I’ll assume that the 11.2oz (330mL) German Weihenstephan Hefeweizen bottle that I purchased at the local beer shop has enough strength to contain the Hefe I fermented at home with the Weihenstephan yeast strain, strength being defined here as bottle mass over volume.

That is, since the Germans tend to overengineer things, I should be safe if my bottles are of the same weight as the Weihenstephan bottle or stronger, per ounce. Fair enough assumption, right?

Measuring bottle weight per ounce of beer

Luckily, I have a local source for Belgian and other imported beer bottles, the local bar. Here are the results of my measurements, using an electronic scale, from strongest to weakest. I’ve highlighted the two hefeweizen bottles for comparison:

1. Orval – custom, grenade-shaped, Belgian – 12.24 oz. weight/11.2 fluid oz. = 1.09
2. Le Chouffe – custom 330 mL, Belgian – 9.98/11.2 = .89
3. Del Borgo – custom, teardrop-shaped 330 mL, Italian – 9.03/11.2 = .81
4. Trillum – custom large format 750 mL, US – 20.11/25.4 = .79
5. Jack’s Abby – 500 mL, US – 13.4/16.9 = .79
6. Weihenstephan – standard 500 mL, German – 13.26/16.9 = .78
7. Unidentified – 330 mL Trader Joe’s Belgian Blonde, I believe – 8.54/11.2 = .76
8. Barrier – jug-shaped 500 mL, US – 12.59/16.9 = .74
9. Baltika – custom, hourglass-shaped, Russian – 12.52/16.9 = .74
10. Samuel Smith – standard British 12 oz. – 8.61/12 = .72
11. Weihenstephan – standard 330 mL, German – 7.76/11.2 = .69
12. Stone – standard US 12 oz. – 8.11/12 = .68
13. Rogue – standard US 12 oz. – 8.08/12 = .67
14. Xingu – lightweight 500 mL, Brazil – 10.55/16.9 = .62
15. Flying Dog – standard US 12 oz. – 7.13/12 = .59
16. Unidentified – stubby 12 oz., US – 6.91/12 = .58

Findings

Several trends became apparent after weighing a lot of bottles.

Standard US bottles are the weakest. While there were several US breweries with strong bottles, they tended to be large format or one-off special beers. Standard crown-top 12 oz. beer bottles, what you see for 90% of the market, are actually very thin. They’re all thinner than the weakest German bottle. Since they are recyclable, not refillable, this makes sense.

Belgian bottles are the strongest. Orval was the only bottle to weigh over one ounce in weight per fluid ounce of beer it held. For the overly cautious, you couldn’t go wrong with a combination of Orval or classic 500 mL hefeweizen bottles.

“Standard” crown-tops aren’t standard. While they may look the same, the standard 12 oz. glass bottle – think Saranac, Sam Adams, Brooklyn Lager – is not always the same weight. Notice the difference between Rogue and Stone vs. Flying Dog.

German hefeweizen bottles aren’t even that strong. Surprisingly, the smaller of the two German hefeweizen bottles came in near the bottom of the rankings. In a way this is good news, because it means more bottles are bomb-proof. Either that or the Germans have been cutting corners lately to supply the export market and these are actually engineered to be disposable.

Post-mortem

Several months after bottling, I have had no bottle bombs. The (over-)carbed beer must be poured into a separate glass because it slowly foams out of the bottle, which is to be expected. All in all this experiment was a success, as it produced a tasty true-to-style ale. I can’t say whether weaker bottles would have been fine, but I am glad to not have found out the hard way as I mop and pick glass shards out of the ceiling.