Hi Hamish,
we make perry on a very small scale, around 100 litres on the go at the moment. We've been trying perry for about 9 or 10 years now and after quite a few mishaps we now have (hopefully) sorted a reliable, repeatable method before we start experimenting.
We use all sorts of pears that are mostly ripe but not over ripe. We have a big old tree that has very odd pears which are under ripe at time of pressing, they are either culinary or perry but the rest are mainly desert pears. We are fastidious about the quality of pear, no bruising at all and no blette fruit either. (I thought I read that bletted fruit was a bad idea?) This is the first year we've not used roadside pears that could possibly be perry pears, mainly because we have so many of our own this year. I hope this doesn't have a negative effect on the perry, I guess we'll know at bottling.
After pressing we use malic acid to bring the ph down to acceptable levels (this is the secret really), to around 3.8 or less (from abour 4.5-4.6), then use SO2 at 200ppm. After a day we add EC1118 champagne yeast. Generally the starting sg is around 1055. We bottle when it looks like it's stopped, (SG is no use here as I've been told it'll vary year on year according to the amount of sorbitol there is), and add a teaspoon of sugar for carbonation per 500ml bottle. Drinkable the following summer but doesn't keep as long as cider so best drunk within a year.
I actually don't like any perry I've bought in the shops as I think they all have an off flavour which ours had the first few times we made it. But the last two times we've made it, it has been so delicious, really creamy, a top quality drink.
If this year's works I might experiment with adding apples to bring down the ph but that might impact the wonderful smoothness and flavour we get. I have also grafted a proper perry pear scion onto two of our trees but it's taking an age to produce fruit. It might seem obvious but introducing cider apples to our cider made a huge difference, so I'm wondering if perry pears will have the same effect.
Hope this helps.
Nik.