I just kegged my English Bitter, after 3 weeks in secondary, as usual I put about a half gallon in bottles to allow for head space in the keg. I guessed at the amount of priming sugar to put in the bottles, about a teaspoon per bottle. By the time I put the sugar in the last bottle I went to cap the first bottle and a few of the bottles were foaming over. I lost some beer, and everything will probably be fine, but I have never had bottles spontaneously foam as soon as I add sugar. Has anyone seen this happen before or know of any explanations as to why this happens.
The fermentation was done, the og was 1.05 and the fg was 1.015. I didn't do anything differently, so I am wondering what caused this foaming.