I want to make sausage rolls the night before and store them in the fridge before cooking. I am worried that the sausage meat will make the pastry go soggy. How can I prevent this?
At work the butcher makes 100's of sausage rolls in batches. We then cook 1/4, fridge 1/4 and freeze 1/2. We never have any issue with them being soggy, regardless of storage method. To be honest in a taste test you'd have no idea which was which.
Also once cooked (as long as cooked properly) they don't go soggy for at least 2 days in the fridge.
I'm assuming you will be using puff pastry as per tradition. If so don't forget to allow the rolls to stand at room temp for 15-30min before cooking as it will help with the "puffing".
I understand that you want to store unbaked saussage rolls and bake them the next day.
IMHO you should be fine as long as the filling isn't too wet. Chill the pastry and the filling well before assembling, this will firm up the fats and reduce seeping from filling to pastry dough. Same goes for puff pastry.
If you want to be extra sure, you need to introduce either a "protective layer", e.g. a slice of bacon or cheese or a sprinkling of something "absorbent" like breadcrumbs (but add a few herbs to the crumbs). This will change the saussage rolls a bit, but if done right, people will think it's supposed to be that way, kind of a fancy twist.
Honestly they will be best freshly cooked but there are few things you can do.
Make sure they are cooled when you put them in the fridge to reduce condensation. You will want to use the oven not a microwave to re heat for serving.
You could also try par cooking them and finishing them in the oven before serving that would help make sure crust is nice and crispy and still cut down the time needed to cook them when you want to serve them.
My personal though is par cook them, I am not sure how long would be best though.