How I helped to anoint PJ Harvey at music's biggest night

The Independent's Elisa Bray was one of the judges who chose the Mercury Prize winner this week. She reveals the passions behind the process

Having spent many a summer deliberating on the Barclaycard Mercury Prize shortlist as a music-loving student, advising friends on which artists to put their money on, and then shouting about it from the pages of this very newspaper, I jumped at an invitation to join this year's panel.

It's a funny business, being on the other side of the fence. There's a certain responsibility that comes with selecting the album of the year and, as a judge, with the criticism that you're inadvertently inviting, it's the equivalent to wearing a fur coat. There are always going to be outraged music fans demanding why so-and-so didn't make the shortlist, and this year it was "Why isn't Wild Beasts' Smother on there?", and "Where are The Horrors?"

In 2008, it was declared that the judges "got it right" when Elbow, after 20 years of creating music, secured the prize for The Seldom Seen Kid. A year later Speech Debelle won, over the more commercially successful Florence and the Machine. The Mercury Prize pays no attention to what is commercially successful or indier than thou. Our mission as judges is to select the albums that best represent 2011 in music; albums that we love and we think you'll love, too.

Let me take you back to the beginning of the process, in June. An iPod and two enormous boxes full of CDs were delivered to my front door, and would occupy the floor space of my living room for the next three months. They contained around 250 albums by British and Irish artists, although it seemed more like 2,000. While the competition embraces all genres of music, contrary to what's often believed we received no stipulation on including a token jazz or folk artist. Comparing genres is a challenge best summed up by Antony Hegarty in his 2005 acceptance speech for Antony and the Johnsons' I Am a Bird Now: "It's almost like there's a contest between an orange, a spaceship, a potted plant and a spoon. Which one do you like better? It's mad."

Some albums I found easier to eliminate than others. Other albums I already knew and loved.

Any social life was replaced by nights spent at the CD player and notebook. Each journey on London transport was spent plugged into headphones – not ideal for appreciating King Creosote and Jon Hopkins' beautiful, understated Diamond Mine, but good for brightening the journey with Katy B and Tinie Tempah. A holiday was spent for the most part inside a chalet, further eliminating albums, while everyone else went surfing. I'm not complaining. The main pleasure of being on the panel is the discovery of new artists. I'd somehow missed Diamond Mine, while Gwilym Simcock's piano compositions, making use of the instrument as percussion, might be my first jazz love.

The first judging meeting takes place at a central London venue. I was expecting a casual round-the-table chat over a cup of tea, but a large square table with elegant place names and a dish of fancy biscuits suggested otherwise. We passionately discussed the merits of each album, with a view to reaching the shortlist of 12. Each of the 12 judges (presenters, artists and music journalists) was invited to boldly champion their favourite artists. P J Harvey was my favourite to win, followed by Anna Calvi, the most striking rock guitarist/songwriter to emerge in the past year. I spoke out for hip-hop newcomer Ghostpoet, whose melancholic, bleak portrayal of urban life I find compelling, and James Blake, who turns experimental beats, empty spaces and effects into somethinghaunting, melodic and emotive. If a judge doesn't support an album, they don't speak, which makes for a positive discussion and gives each album a chance. When the shortlist was revealed, yes, I lamented the exclusion of a couple of my choices. However, the shortlist that emerged was an accurate reflection of the judges' enthusiasm, and turned out to be one of the best-received lists by the public in the 19-year history of the Mercury Prize.

Not by everyone, though. At the shortlist announcement on 19 July at the Hospital Club venue, a few metal lovers gathered outside with placards asking why the Mercury Prize ignores metal, in support of their snubbed band Bring Me the Horizon. That was it for two months – except for continuous listening. We would reconvene for the second judging meeting at Tuesday night's awards ceremony at Grosvenor House, where all the artists would be celebrated for achieving one of the albums of the year. The bookies may have decided Harvey as the favourite, but when I walked into the judging room none of us had any idea where the discussion would go and who would win.

This meeting seemed ruthless by comparison to our first meeting. In an elegant room deep within the hotel, the early evening hours were spent discussing the albums. Later, stepping into the Great Room, as music industry types debated the list and swigged wine, the weight of responsibility hung heavy. Nerves were soothed with wine as Tinie Tempah made a storming start with "Pass Out", changing his lyrics to "I've done the Mercurys, but I've never been to Scunthorpe." Harvey's "The Words that Maketh Murder" was stunning. Crowds typically chat through the acoustic and folk performances, but not this night. The room fell silent, mesmerised by King Creosote and Jon Hopkins's tender performance.

During the second half of the judging session, tensions peaked. Things can get heated in that room. People had different views, voiced clearly; pressure mounts as the minutes tick by to the point where we must decide on who is most deserving of the prize. Through discussion, artists were eliminated one by one until one remained. I can't have been the only judge to have felt a pang of guilt on letting some favourites go.

At 9.40pm, just minutes before our deadline, we had the winner of the £20,000 prize. I couldn't be happier with what we all finally agreed was the album of the year. Now we had to face the reaction of the crowd, but I had an inkling it would be less like the ripple of bemused surprise at Antony and the Johnsons' win and more the rapturous ovation that greeted The xx last year.

When the whole room gave Harvey a standing ovation, we knew that we had made the right decision. Still, there will always be dissenters. Trawling through Twitter, I unearthed comments such as, "Surprise, surprise PJ Harvey won the mercury awards. Did the judges listen to any other album but hers?" and another: "This is shocking! Judges need their ears cleaning out!" That's some bad karma.

But it is wonderful to hear that on the back of Harvey's win, Let England Shake is headed for the Top 10. That the prize draws attention to all the albums on the shortlist – and what we found to be the best album of the year – is worth the many hours spent listening to hundreds of albums.