miércoles, 21 de junio de 2017

Thermodynamics is the key to great barbecue

By J.C. Reid

Is making barbecue an art or a science? Like most things that can be characterized this way, usually it's a little of both.

Publicly, pitmasters tend to play up the former - producing world-class barbecue is some type of magical process that depends solely on intuition and experience. But, in reality, it comes down to general knowledge of how heat and air flow affect the temperature used to cook meat.

Consistent cooking temperature is the key to making great barbecue. Using the traditional "low and slow" method, a pitmaster wants to cook his or her briskets at about 225 degrees for eight to 14 hours. Any significant variation will yield over- or undercooked meat, which is the sign of an inexperienced pitmaster.

Backyard barbecuers know the struggle for temperature consistency. Anyone who has cooked a brisket in a smoker at home will experience the "stall," when the meat's internal temperature stops rising at about 150 degrees. Because of the simplicity of the equipment, making a bigger fire and increasing the temperature usually just results in overcooked meat.

The preferred method of controlling temperature in this case is known as the "Texas crutch." This involves wrapping the brisket in aluminum foil to help retain heat and force the meat's internal temperature to rise to the correct cooking temperature.

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The "stall" is a microcosm of the challenges faced on a daily basis, and on a much larger scale, by professional pitmasters. Fortunately, they have a much larger arsenal of techniques and equipment to deal with temperature issues.

All commercial smokers are based on the same thermodynamic principle known as the "stack effect." When a fuel source like wood is burned, the heated air rises and "draws" more air into the wood to keep it burning, creating air flow. It's the same idea that produces the "draw" for a chimney.

Precisely controlling the heat and air flow produced by the stack effect is the holy grail for pit makers. There are basically three types of barbecue pits, which are distinguished by how much intervention is necessary by the pitmaster: manual, semiautomatic and automatic.

Manual pits include the all-wood-burning, offset barrel or brick pits. On one side of the cooking chamber ("offset" from it) is a firebox where the wood burns. On the other side is the flue where the heat and air rise and escape. The heat and smoke produced in the firebox flow over the meat in the chamber, cooking and flavoring it, and then flow out of the flue on the other side.

Pitmasters have several techniques in this case to control the temperature. They can add wood to the fire or increase the air intake at the firebox, generating more heat. They can also open the flue wider to increase the air flow.

However, even with a consistent temperature and air flow, these pits can have temperature differentials within the cooking chamber known as "hotspots." Pitmasters combat these hotspots by diverting the air flow or absorbing heat. Strategically placed concrete blocks or steel "tuning plates" within the cooking chamber are the traditional tools for this task. BBQ Pits by Klose in Houston is recognized as the leading manufacturer of the offset barrel pit.

For pitmasters who want slightly more automation in producing consistent temperature and airflow, semiautomatic pits are the solution. In this case, the firebox is below, the cooking chamber in the middle and the flue above. Using a thermostat and a series of mechanical dampers, the pit automatically dispenses heat and air from the all-wood-burning firebox into the cooking chamber based on temperature fluctuations. J&R Manufacturing and A.N. Bewley Fabricators, both out of Dallas, are well-known producers of semiautomatic pits.

Fully automated pits use the same damper system as semiautomatic pits but also use a gas flame, rather than burning wood, as a last resort to control temperature. Southern Pride and Ole Hickory are two well-known brands. Though great barbecue can be produced on these "gas-assist" pits, many pitmasters rely solely on the ease and convenience of the burning gas, which results in the mild flavor of roast beef rather than the smoky deliciousness of true barbecue.

Ultimately, the art or science of barbecue is determined by the equipment used. Manual pits require more experience (art), while automatic pits rely more on pit engineering (science). Semiautomatic pits require a little of both.

Columnist, Houston Chronicle


domingo, 1 de enero de 2017

Cómo los terremotos han sacudido la Tierra en los últimos 15 años

En los últimos 15 años la Tierra ha sido sacudida por algunos de los terremotos más devastadores desde que se lleva registro.

En 2004 un sismo de magnitud 9,1 en la escala de Richter dio pie a un devastador tsunami que arrasó la línea costera del océano Índico y se cobró unas 230.000 vidas.

Y 2010 fue un año particularmente trágico para la región. En Haití un terremoto de 7,0 provocó la muerte de 220.000 personas y meses después Chile fue sacudido por el peor terremoto desde 1960.

Ahora, la Administración Nacional Oceánica y Atmosférica de Estados Unidos (NOAA, por sus siglas en inglés) publicó esta animación que hace un repaso de todos los movimientos telúricos de al menos 6,5 en la escala de Richter que se han registrado en nuestro planeta desde 2001.

En total ha habido 20 terremotos de al menos 8 grados en la escala Richter. Los tsunamis de diciembre de 2004 y el de Japón 2011 fueron los más poderosos.

Un terremoto se produce cuando la corteza terrestre libera energía, por lo general esto pasa en los límites de las placas tectónicas. Estas son fragmentos de la capa terrestre que se mueven como un bloque rígido.

La agencia científica estadounidense estima que cada año se detectan unos 500.000 movimientos telúricos. De ellos, se sienten 100.000, pero sólo 100 causan algún daño.

Así que experimentar un terremoto de magnitud 9,1 es poco frecuente, pues para ello se necesita que las placas tengan una concentración alta de energía.

No obstante, esta animación nos recuerda que la Tierra está expuesta a constantes terremotos y lo terrible que algunos de estos temblores pueden llegar a ser.

Según Naciones Unidos, el tsunami del océano Índico requirió del mayor esfuerzo de ayuda internacional que se haya registrado en la historia.

Fuente: BBC