There are many methods of recording a grand piano with their various pros and cons which are suitable for different applications. I recently did some experiments to try and figure out the best way of making a stereo recording in a reverberant room (in this case, a church).
This video demonstrates six different methods but it is just an introduction. There is so much more experimentation that can be done by moving the microphones around the room. Techniques demonstrated are XY, AB cardioid, AB omni, ORTF, Mid-Side and Blumlein.
Basic microphone techniques are taken from Bobby Owsinski’s excellent textbook The Recording Engineer’s Handbook. The microphones being used are Sontronics STC-1 and Behringer B-2 Pro. The music is Piano Parchment by Johnny Pearson – better known as the TV theme from All Creatures Great & Small. Huge thanks to tame pianist Matt Timms for tickling the ivories at All Saints Church, Long Ashton.