Having recently discovered the delights of home-baked hot water pastry (it is easy to make and absolutely delicious), I'm looking to use this with a chicken and white sauce filling. Traditionally this pastry is used with dry fillings such as sausage meat etc.
Is this combination at all possible while retaining the crispness of the pastry or will I inevatibly be heading towards "Soggy bottom misery" ?
In short:
Yes, with some easy modifications for more safety margin:
Longer answer, taken from the relevant bits of another question:
Using the recipe ratios from the King Arthur Baking Company page for hot water pastry, we have:
The process for making and using the dough, where the water and fat are added and kneaded together, results in the flour starch absorbing and partially gelling from absorbing the hot water, then coated with lipids once all the moisture is absorbed.
During baking the pre-gelled starch heats and gels further until the water is driven off as steam, then the starch dehydrates and fries with the lipid coating.
The composition of fillings and pastry, broken down into 3 general groups, are:
- water
- fats and oils (lipids)
- non-fat solids, i.e. milk and meat proteins, starch
Pastries baked with liquid fillings typically rely on the insolubility of oils and water to keep the fillings from leaking through. This is usually done with high fat/oil content in the pastry and high water content, low fat/oil content in the filling:
- fruit pies, strudels, and tarts with puff pastry made of mostly starch and fat
- cheesecakes with graham crackers bound in fat
- various applications of Greek phyllo pastry
Since pastries will usually heat from the exterior to the centre, steam from the pastry will be forced toward the filling. This low steam pressure, along with the hydrophobic/water-repelling lipid coating, is typically enough to prevent water in low moisture fillings from penetrating and remoistening the starch.
With higher moisture fillings the increased mass of water may overcome the exterior steam pressure. To counter this, we can 1) make the pastry more hydrophobic, 2) make the filling release less water, or 3) intercept the released water before it remoistens the pastry:
Blind baking the pastry with egg wash will give the inside surface a set egg protein layer that acts as a slight barrier to moisture. Coating the inside with more fat/shortening will accomplish the same - though not with regular butter, which will release water.
Adding a small amount of gelatin to the filling (~1 tsp/cup) will bind some moisture and add extra viscosity to the filling with protein, binding more strongly than starches in béchamel/white sauces. At this low amount of added gelatin the filling will still be liquid when served warm.
A light dusting of starch or gelatin under the filling and on top of the pastry and fat layer will hydrate as the filling releases moisture, with the goal of retaining the moisture that would otherwise seep to the bottom. Gelatin is preferred due to the properties described in 2) above, dry pre-gel starches the next ideal option with a higher moisture holding capacity and lower risk of graininess from underhydration, then corn or rice starch next for their higher gelling point before over-gelling and losing viscosity. Flour is not ideal.
I haven't made hot water crust pastries with liquid fillings, but I've had them before and they were good, so it can be done. There wasn't any issues with sogginess that I could detect.
When you make a meat pie with hot water pastry the inside is usually pretty solid so you don't get any pressure on the inside of the pastry which will deform or split it, you add liquid after baking when it's hardened and can withstand the pressure. If I were going to use hot water crust pastry I'd use a pan like any other pastry so the sides are supported. You could try a free standing pie, the crust may need to be pretty thick to hold shape, some experimentation would be good, I'd love to hear the results.
