Well now that I have got your attention, we today are not talking about arson and acts of terrorism. We are talking about glass bottles bursting because of excessive pressure buildup. Almost all home brewing forums would have warned at some point in time about bottle bombs. Today we will talk about what they are and how to prevent them.
The prime reasons for exploding bottles are:
- Early bottling: If your fermentation is not complete, the yeast will continue to ferment in the bottle and create excessive pressure. The best way to prevent that is to use a hydrometer and check if the residual gravity is constant for 3 days (i.e. yeast has completed its work)
- Excessive priming sugar: The link below has some bottle conditioning tips which are useful in calculating the right amount of priming sugar that has to be used to create the right amount of fizz.
- Refermentation: Common in sweet wines and sparkling wines. As you can see from the video. If the right amount of wine stabilizer is not used, unpasteurized wines tend to get eaten up by residual yeast. This can lead to excessive pressure.
- Recycled bottles. Bottles that have scratches, nicks develop micro-fissures that lead to weak spots that can break off once excessively pressurized. Although commercial beer bottles can hold up to 12psi pressure, I would not recommend going beyond 4-6psi for recycled bottles. (this is good enough for most beer styles, but your sparkling wines, champagnes and fizzy ciders might feel not carbonated enough. One good alternative is to use beer cans and kegs instead of bottles.
- Infection: You might have completed the fermentation before bottling, but if the bottle was not cleaned properly, then a new infection microbe (usually bacteria) could restart fermentation and build-up of CO2.
- Sunlight and high temperatures: These can alter the chemistry of your beverage, breakdown of complex sugars (malt) and restarting of fermentation.
- Improper mixing of sugar: If one bottle has a high amount of sugar and the second less, then the uneven pressurization can lead to further problems rather than solving them.
Exploding glass bottles can lead to injury and glass shards are a menace. So please excise caution and proper safety. Fermentation is easy, but shortcuts in safety and procedure can only lead to accidents.