The other day I was passing by a supermarket from which came the gorgeous smell of roast chicken. Like Proust and his madeleine, this brought back memories of the traditional Sunday roast at home when I was a kid. Now that I am a chef, I am rarely able to recreate this for my customers as it is difficult to serve a whole chicken or leg of lamb on the same table.
How to make sure that the outcome of a roast becomes a great gastronomic experience everytime? I thought kitchen science could give it a push to the right direction.

Before starting to cook our roast, I would like to talk about the chemical reaction behind the flavour of roasted meat. It is produced by a chemical reaction called the “Maillard reactions”. The understanding of this principle will guaranty us a great outcome every time.
In simple words, the maillard reactions begin when, under the action of intense heat, a carbohydrate molecule (a sugar) reacts with a molecule of amino-acid (a protein) to create an unstable, intermediate structure. This new molecule called Amadori by-product will, then, be able to combine to other compounds in the meat, further along, during the cooking process. The final result of the Maillard reactions, is hundreds of different by-products that combined together create the meaty savoury flavour of the roast crust.

Just few words here about how to choose a cut of meat for a roast.I’m not going to talk here about the birds as most of them are eligible for roasting. But choosing a cut of lamb, beef or pork in the supermarket isn’t always simple as most of us go by the price. In an animal there are two types of muscles, therefore two main types of cut of meat.
The first one, are the working muscles like the leg, shoulder and arm. They do most of the work of supporting the animal, they contain a large proportion of what is called reinforcing connective-tissue, rich in collagen they are tough and require a long cooking to dissolve that collagen.
On the other hand rib, short loin and sirloin do less work, so have fewer connective-tissue and are tender and more suited to short cooking at high temperature.
A roast is always done in three steps : searing, cooking and resting.

The first step in cooking a roast is to sear the meat. It is simply done by cooking every sides of your cut of meat or bird (for this one stick a large wooden spoon through the inside cavity, it is then, easier to move it around), for a short time, in a very hot pan to a golden brown color. This is an important step, because this operation will ensure, first of all, that the meat will keep its moisture during the cooking process by creating a protective shell. It will also lay the base for the Maillard reactions by generating the Amadori by-product.
There are few tips to obtain a good searing result. First, make sure that your cut of meat or bird is dry on the outside. Then do not season the meat yet as the salt will extract some moisture out of the meat and the pepper will burn and give a very bitter taste. Using a brush, oil the meat on all its surfaces (do not over do it though!), it will help the transfer of heat from the pan to the meat.

The second step is the actual cooking of your cut of meat. This operation seems pretty simple, just throw the meat in a roasting tray, put it in the oven for what ever amount of time and forget about it. In fact it isn’t that simple. If you want to achieve a crispy outside crust and a juicy, tender center, you will have to keep a close eye on the temperature of the oven.
Kitchen science tells us that the principle of cooking meat in the oven is to minimise the loss of moisture and compacting the meat fiber while maximising the conversion of tough connective-tissue, collagen, to fluid gelatin. Unfortunately, these to actions are contradicting. To avoid the loss of moisture the meat cannot be cooked over 130-145F or 55-60C (at core) but the collagen needs prolonged cooking above 160F or 70C for a long period of time. This is a problem when roasting a chicken, turkey or other birds because the meat in the breasts is made of fewer connective-tissue, but the meat in the legs is mainly made of such tissue. The result is dryer, tougher meat in the breasts, and under cooked juicy meat in the legs. There is the answer to why meat connoiseur will prefer the leg to the breast of a roast bird.
So, to obtain a good result while roasting your cut of meat or bird, start with a relatively hot oven 180-200C, turning the meat from time to time (use a wooden spoon, you don’t want to break the protective shell created earlier) until the crust is done. Then, only, reduce the temperature of the oven to 160-170C to cook the meat trough. When roasting a bird, protect the breast with a bit of tin foil to avoid that they over-cook. You can season the meat now, just before putting it in the oven.

How long should you cook your roast? There is no definite answer to that. The usual will be a minutes per pound of meat. The new research on the subject shows that isn’t accurate, the cooking time is proportional to the weight squared, or to the weight to 2/3 the power of the oven. So, the best way is to check the temperature at core or like chefs do by touch.

There a guide line on doneness :

- Bleu 110F/45C, soft raw like to the touch.
- Rare 120F/50C, becoming firmer to the touch.
- Medium-rare 130F/55C, resilient to the touch.
- Medium 140F/60C, begins to shrink, losing resilience, exude juice when pressing it.
- Medium-well 150F/67C, little resilience, less free juice when pressing it.
- Well-done 160F/72C, stiff, dry.
- V well-done 170F/75C, stiffer, very dry, grey color.

The last step is the resting. The purpose of this final step is to allow the meat fiber to “relax” and allow the juices to migrate to the center of the roast. It take from 5 to 15 minutes depending on the doneness of the meat. A rare meat will require 5 minutes and a v-well-done one 15 minutes. Little tip place the meat on rack or grid on the top of the opened oven door while the oven is still hot.
Then skim the fat out of the roasting tray, put it on the ring, add a couple of carrots coarsely chopped, an onion prepared in the same way, 2 crushed cloves of garlic, some thyme and halve a bay leaves. Cook it for 10 minutes, add a cup of wine and scrub the brown bits at the bottom of the tray. Allow to simmer for another 10 minutes. Filter that juice it make a great gravy base or as we call it in France “jus de roti” (roast juice).
I hope it can help!