According to EU regulation 1178/2011, the only condition is that you have at least 12 takeoffs and landing and 12 hours (of which 6 as PIC) and one hour total flight time ("block time") of "refresher training" within the last 12 months before the end of the validity of the single-engine piston and/or touring motor glider class ratings.
As far as I can tell, the one hour of refresher training doesn't even have to be one contiguous flight, but can be spread out over multiple flights.
Only a proficiency check (i. e. checkride with official examiner, which is required if you don't have the prerequisite flight time) needs to be performed within the last 3 months before expiry.