Kitchen Science: Pastry

Ah, pastry. Pastry is one of my weaknesses in life. Pasties and pork pies and strudel, and apple pies and lemon meringue pie… and custard slice and cream puffs. I could go on. Sometimes I think these kitchen science posts read like the food porn inside of my mind; like delicious science with added drooling.

Pastry IS amazing, though. It’s one of those things that sort of blows your mind when you really think about it… the same basic ingredients, in slightly different amounts and proportions, mixed together in different ways can result in such incredibly different textures. It’s kind of miraculous, because you’d think that flour, fat and water mixed together would always end up the same. I would have thought so anyway, but luckily chemistry has other, far tastier ideas than me.

Because there are lots of different types of delicious pastry, this is going to be a two-parter. I’m currently taking bets on how long I last writing these two posts without caving in and making a pie (odds are on that it’ll probably be about 3 minutes, if I’m feeling strong)

What’s in pastry, then? Flour, fat and water. And possibly some other bits and pieces, but these three are the key players, the stars of the show.

Flour is the structural backbone of pastry; it’s the thing that gives strength and shape to the whole affair. However, it’s not quite as structured as it is in cake, for example. In cake, gluten from the flour forms a stretchy web that spreads throughout the whole cake and holds the whole business together. In pastry, the flour particles are deliberately segregated in specific ways, and then coated in fat.

Fat is key to pastry, it coats the flour particles and keeps them apart, isolated into a tiny prison, with no water allowed in or out. Fat is always a bit fascist about water. When the mixture is heated, the gluten in the flour particles can’t get to water, becuse they fatty prison guards won’t let them, so instead they gelate together in terror, to form a dry and crumbly texture. When you eat this, you get the combination of crumbly gluten and melty butter. Who’d have thought terrified isolated flour particles would taste so good?

The amazing thing about pastry to me though is the differing textures you can get; and this depends on the way that the flour particles are segregated. In crumbly pastries, like shortcrust, the butter is mixed into the flour in chunks that are slowly integrated together by manually… squishing them together. I believe the technical term is rubbing, but I prefer squishing. This results small lumps of flour, clinging together, surrounded by butter. In some shortcrust pastries, egg is also added and the protein from the egg provides an extra scaffolding, to stop the pastry crumbling away completely. Although it is still possible to create pastry that crumbles completely, even with egg, as I can testify. I’ve been there.

Mmmm. Shortcrust pastry. I wish I could say I’d made this, but when I make pastry, it doesn’t last long enough to be photographed.
Image source.

By comparison in, puff pastries, or laminate pastries, the flour and gluten is distributed differently. Rather than being squished into the butter, and trapped, the process is longer and far more tortured for the gluten. If you were so empathetic that you could feel sorry for flour, you’d definitely never make puff pastry. Equally, if you were highly impatient, you probably wouldn’t either.

So, to make laminate pastries, you mix flour with a small amount of water to form a just-about dough. Then you place a block of butter, heated until it’s just pliable but not completely melted and useless, on top of the block of dough. Then, you fold the whole thing up, and roll it out. Then you turn it, fold it, and roll it some more. In between bouts of rolling and folding, you chill the whole business in the fridge so that it’s good and cool. The process of rolling the dough allows the gluten to develop, but it is a bit tortured and stressful. The chilling in the fridge stage gives the gluten some much-needed downtime in which to relax. You know, before it gets tortured again. The result of this time-consuming process is that the flour-gluten is stretched into hundreds and hundreds of teeeny tiny thin layers, isolated between layers of butter. This differs to shortcrust pastry, where the flour particles were in clumps, not super-thin sheets.  And the result of this is that when the whole thing heats up, the flour particles do still cling together, but they form sheets not crumbly chunks. And the evaporation of water into steam between the sheets causes them to puff right up, into a light, crunchy, delicious sheet.

I can forgive the torture of gluten for this.
Image source.

So, that’s the basics of two types of pastry, terrfied and tortured flour plus delicious buttery prison warders. Come back next time for more science drooling, and more pastry.

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One thought on “Kitchen Science: Pastry

  1. I think I was never scared of making pastry as I had a good recipe (Women’s Institute Cookbooks for the win) and just followed it, but it is cool to understand why it does what it does so thank you Katie!

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