Permanent link to this article: https://animatedscience.co.uk/2014/why-you-cant-travel-at-the-speed-of-light
Feb 22 2014
Vector boson fusion? | Jon Butterworth | Life & Physics
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Feb 21 2014
Men’s Health: Could Pizza Prevent the Stomach Bug? http://google.com/newsstand/s/CBIwx6DU4xE
Permanent link to this article: https://animatedscience.co.uk/2014/mens-health-could-pizza-prevent-the-stomach-bug
Feb 20 2014
The science and magic of pastry | Andy Connelly
The science and magic of pastry | Andy Connelly
Varying amounts of fat, flour and water in the recipe give the full spectrum of pastry, from delicate tenderness to brittle flakiness
The ‘shortness’ or crumbliness of pastry is determined by the extent to which gluten molecules are allowed to form in the dough. Photograph: Dan Lepard/Guardian
Thu 20 February 2014
If you wish to make an apple pie from scratch, you must first invent the universe. Carl Sagan
Most pies offer a degree of mystery: a top crust that fuels anticipation and hides the wonders to come. They allow the chef a “reveal” moment, when the blackbirds come flying out. Jam tarts – the recipe below – may lack this element of surprise, but they excel in terms of simplicity. No custards, crumbles, or curds are required. No complex parcel folding, edge-crimping, or pretensions. Just lovely acid-sweet jam and an explosion of buttery pastry.
Pies and tarts have always been chameleon-like: sweet or savoury, hot or cold, sophisticated or humble. The common factor is always the pastry, the nest in which the myriad treats can be stored. Unfortunately, its exact history is difficult to pin down, pastry having been the forgotten essential in many old cookery books.
The main use of pastry in the ancient world seems to have been to cover meats and fowls during baking to keep in the juices, steam the contents and act as a barrier against contamination. This tradition was carried on in medieval northern Europe where they had the advantage of solid fats, as opposed to oils, allowing for more substantial pastries. They made stiff pastry “coffyns” that could act as containers for stews in the oven, and then be carried to the dinner table. This pastry pyrex was not intended to be eaten by people; well, not rich people anyway.
The three primary ingredients of pastry are fat, flour and water. The ratio and handling of these ingredients give us the full spectrum of pastry, from delicate tenderness to brittle flakiness. Traditionally, the jam tart has been made with shortcrust pastry – “short” because it comes apart into small, “short” irregular particles. However, there is no reason why you cannot make jam tarts from any type of pastry – I’ve tried most of them. The recipe below is for 10 classic shortcrust pastry tarts but it can easily be modified. One common modification is to replace most of the water with an egg to enrich the flavour of a shortcrust pastry and to provide proteins, which help bind it.
200g plain white flour
100g butter (at a cool room temperature)
About 40ml (3 tablespoons) cold water
Jam – of your choice
Cut the fat into small pieces with a knife and mix with the flour. Using your fingers, rub the fat into the flour until the mixture resembles rough bread crumbs. Now sprinkle a little water at a time onto the surface and mix with a knife, then your hands, until a ball of dough forms with the texture of slightly dry playdough.
Keep handling to a minimum as it is not cold hands (or a warm heart) that are key to quality shortcrust pastry, but minimising the formation of the stringy, elastic protein gluten. By rubbing fat into flour before adding any liquid, small cells of flour coated in fat are formed, giving shortcrust pastry its fragmentary, discontinuous, particulate texture. This layer of fat makes it difficult for water to hydrate the flour, so structure-giving gluten proteins cannot form. The more coated the flour cells, therefore, the less well they will bind with their neighbours and the weaker (shorter) the pastry will be. However, if the flour is too well coated the pastry will not hold together and will become difficult to work with. This can happen if you use oil or if the solid fat is too warm.
The type of fat also has a significant impact. For me, flavour is the most important consideration and so I always use melt-in-the-mouth butter. However, it has its disadvantages. Between 15 and 20C butter has a solids content ideal for handling; outside this range it is either too fluid or too hard. This handling range is particularly important for laminated pastries, such as filo, which require layers of solid fat. For shortcrust pastry, a lower solids content is useful as it helps coat the flour. Manufacturers have spent a lot of time and money developing oil-based “shortenings” that have specific textures over large temperature ranges. These can produce great-looking pastry but the higher melting temperatures mean that the fat doesn’t melt in the mouth, resulting in a waxy “mouthfeel”.
Pop in the fridge
Wrap the dough in greaseproof paper or cling film to prevent it becoming dry and the fat absorbing any unwanted flavours from the fridge.
Pastry of all kinds needs to be left to rest in a cool place for at least 15 minutes. This allows the fat to resolidify after handling, making the pastry easier to work with and ensuring that it will hold its shape during the early stages of cooking. Resting also allows two other processes to occur: the diffusion of water through the dough and the relaxation of gluten strands.
When making pastry, flakiness and tenderness are at odds. Tenderness is favoured by conditions that discourage the development of gluten. Since hydration encourages gluten formation we add as little water as possible and then let it diffuse and become well distributed. By contrast, laminated pastries require layers of pastry with sufficient gluten to hold their shape, so a little more water is often required. The ultimate form of this glutinous type of pastry is filo, which in its raw form consists of one thin glutinous layer. Filo pastry contains very little fat itself but relies on fat being added later in between incredibly fine sheets, allowing them to separate during cooking, and so shatter in the mouth into fine delicate shards.
Water content is also affected by the type of fat used. Pure fats such as lard contain virtually no water, whereas butter is about 15% water, and margarine has an even higher water content. For this reason many people mix butter and lard to combine the flavoursome properties of butter and the better texture that lard provides.
Gluten strands will form in your dough while you are working it; they will stretch and twist, giving elasticity to your dough, known as “bounce back”. The more you work with your dough, the more gluten will develop, leading to an elastic dough that will shrink in the oven and lack tenderness. This is why a light touch is so important and why the dough is left to relax in the fridge. Here the strands become more settled in their new form and so the dough becomes easier to shape, roll and fold, and will not shrink in the oven. A little lemon juice can also aid gluten relaxation and help stop discolouration of pastry during handling.
Sprinkle the work surface lightly with flour and rub the rolling pin with flour. Take your pastry out of the fridge and roll it about 2-3mm thick. Roll using even pressure and gentle strokes away from you, giving the pastry a quarter turn after each roll. Occasionally flip it over to ensure that the pastry is not sticking and dust more flour on the surface as needed.
On paper, the main difference between puff and shortcrust pastry appears to be the fat content. Shortcrust will generally have a “half-fat-to-flour” ratio (by weight) and puff pastries roughly equal quantities of flour and fat. However, fat content is only part of the story. The key difference is in the role of the tourier who rolls the dough out on their chilled marble slabs or tours.
For laminated puff and flaky pastries the tourier will fold and roll the pastry over and over onto itself. This develops strong two-dimensional glutinous layers and traps air between them. This air then expands on heating, giving height to your pastry. However, pastry will stick to pastry unless well lubricated with fat rolled or marbled between these layers. In true puff pastry only about an eighth of the fat is mixed into the dough – the rest is rolled into sheets and interlaced with layers of dough. The result of this time-consuming process is hundreds of layers of fat and pastry which grow in the oven, filling with air and steam.
To create our shortcrust jam tarts, cut pastry circles that are a couple of centimetres bigger than the holes in the baking tray. Black metallic muffin or small pie baking trays work well.
Now it is time to add the sweet heart to your jam tart. Place a small spoonful of jam in the centre of each. Be very careful not to add too much jam as it will boil over the sides of the pie and you will never be able to remove the jam tart from the tray! My rule of thumb is to add just a little bit less than you think you need.
Into the oven
The smell of hot jam tarts in a warm kitchen on a cold winter’s day is heaven. Sugar, fat and fruit fight for attention in your nose, feeding your anticipation. As the temperature of the tarts increases a race will start between the sag of melting fat and the drying of the structure-forming gluten network. This makes oven temperature a tricky decision. The hotter the oven, the more rapidly the gluten network will form, but it is also likely that that the filling will boil over. Lower temperatures will help stop boil-over but might mean the fat melts before the gluten network can form, leading to the nightmare of a soggy bottom. A good compromise seems to be 180-200C.
In breads and cakes the gelatinisation of starch helps give shape. In shortcrust pastry, however, starch is generally less important. In hot water pastry the larger amount of water means that a strong gelatinised starch network has already formed before cooking, giving a very strong pastry to work with. In shortcrust pastry there is so little water that the starch can only partially hydrate. However, in absorbing the little water available it helps dry out the gluten network and so set the structure. Any sugar you added to the pastry will also help dry your pastry and help develop colour and flavour through caramelisation reactions.
As higher temperatures are reached water starts to evaporate, forming steam. In laminated pastries this will push the fat-lubricated layers apart. This is where butter is a mixed blessing – it has a higher water content, which generates steam, but does not separate layers as well as pure fats such as lard. Another problem can occur if you have damaged the layers, for example by pricking them with a fork before “blind baking” a pastry case. But this releases hot air and steam and can prevent the separation of the layers.
Towards the end of cooking, when the surface of the pastry has reached a high enough temperature, Maillard browning reactions will start. Brushing the pastry surface with raw egg will add to these reactions and also forms a waterproof layer, which is again useful in blind baking.
After about 15-20 minutes take a look at your tarts. If the browning reactions have taken place and you have beautifully pale brown tarts, take your glistening prizes from the oven and leave them on a wire rack to cool. This allows any residual moisture to escape and gives you time to make a cup of tea with which to enjoy one of your delicate, sweet-hearted pastries.
Permanent link to this article: https://animatedscience.co.uk/2014/the-science-and-magic-of-pastry-andy-connelly
Jan 27 2014
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Jan 11 2014
Black hole to ‘eat biggest meal’ http://www.bbc.co.uk/news/world-middle-east-25678737
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Jan 01 2014
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Dec 29 2013
Scientists tell us their favourite jokes: ‘An electron and a positron walked into a bar…’
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