Small but rapid change in wort temperature

[yoboseyo]

I left the fermenter at 18C (64F) ambient temperature and the first signs of fermentation started 20 hours in. At 40 hours in, fermentation was very active and I noticed that the wort temperature has risen to 21C (70F), as I wasn't accounting for the increase in temperature due to fermentation itself. I took the fermenter outside and wrapped a wet towel around it and 5 hours later the wort temperature dropped down to 18.5C (65F). Could this rapid drop in temperature cause off flavours to be produced?

 

[TheMadKing]

I think you'll be fine, I use a fermentation chamber where I bump the temperature by 5-10 degrees frequently with no ill effects. I think leaving it at 70 would have been more likely to cause off flavors.