what happens if the first fermentation hasn't ended and I go ahead and prime and bottle my beer?

Question

yea kinda think I didn't let it go long enough, also had other responsibilities other than a brewer so ¯_(ツ)_/¯

Answer 1

Normally, when we are bottling we wait for fermentation to complete and then add a defined amount of sugar that (by calculation or experience) will result in the desired level of carbonation in the sealed bottles. By not waiting for fermentation to complete, you have no way of knowing what your level of carbonation is going to be and you run the risk of "bottle bombs" - see this article for more information:

The bottle exploded in the kitchen and left dark stout covering the walls, counter, floor and cabinets. It was only a 12 oz bottle, but it looked like someone had repainted the kitchen. Glass was also scattered as far as the living room and a small piece had even embedded itself in the drywall. I realized at that point that this homebrewing thing was a lot more dangerous than I had guessed. Someone could have been hurt.

When you bottle, you are confining the beer to a fixed volume. The yeast will continue to ferment whatever sugars are available in the beer, which produces alcohol and carbon dioxide. Here, the alcohol is not a problem, but the carbon dioxide has the potential to be a serious problem. Excess carbon dioxide production will create excess pressure inside the bottle.

Bottles are strong and can hold a reasonable amount of pressure, but the yeast, given the opportunity, are perfectly happy producing enough carbon dioxide to cause explosions.

Options:

1. Hope for the best. Don't worry - it will all work out ok. But maybe not.
2. Store the bottles in such a way that if they start to explode that it is less catastrophic to the rest of your house. For example, sealed cartons will prevent flying glass and beer. Placing the carton in a plastic garbage bag will prevent the loose beer from soaking the carpet. Be aware that chain reactions are a thing.
3. Open one of the bottles every couple of days, paying attention to whether or not there is excessive pressure. If there is, then you want to open all the bottles and relieve the pressure, re-capping the bottles. You reduce the risk of bombs, but may end up with under-carbonated beer (which is still consumable).
4. Uncap all bottles and put them back in your fermentation vessel, wait until fermentation is complete (measure it!), prime (again), and bottle (again). This is not ideal for the beer (oxidation, potential sanitation issues), but it will absolutely prevent bottle bombs.

Even if a bottle doesn't explode while during conditioning, a bottle under stress can explode when it is jostled or bumped (e.g., while being placed in the refrigerator). An unhappy (and dangerous) surprise.