The sound of exploding beer bottles downstairs. Looks like brew 6 was in fact OK and I may well have bottled a day early. Will need to wait and see whether they all blow or only some. Have had three go off in the last half hour.
Update: have been out for a couple of hours looking at nursing hostels (long story). Three more bots have gone off in the 10 minutes I've been back. Not game to go downstairs - the last time I did I suffered cuts to arms and legs when a bottle went off in front of me. I reckon there will soon be 20 litres of beer sloshing around down there, all mixed in with broken glass.
Another update: after having gone downstairs in full protective gear: nine bottles standing out of the 55-odd I filled. What a waste!