Charcoal barbecue. Photo Credit: green.funtimesguide.com
Summer is here and with it brings barbecuing season. While the average charcoal BBQ may seem like a pretty simple appliance there is some solid engineering behind its design.
First let’s look at the charcoal briquettes. An engineer took chunks of wood and organic matter and heated it up in the absence of oxygen to produce an energy dense fuel that is fairly clean burning. This process is called pyrolysis and it removes all the moisture and fumes so that the avid BBQ enthusiast will be able to cook their food without coating it in a black smoke of tiny particles.
The BBQ itself is designed to control the combustion process. By opening and closing vents the user is able to regulate the flow of oxygen to the fuel. This directly affects the combustion rate, the rate at which energy is released in the form of heat.
And, as with any cooking process, heat transfer is an important consideration. When the coals are glowing hot they are emitting a lot of their heat as radiation. Radiation requires a direct line of sight and this is what causes one side of your food to get a nice sear on it before you flip it. When the lid to the BBQ is closed the air inside heats up and this allow for some natural convection, heat transfer from the hot air moved by its change in buoyancy (hot air rises). There is also some conduction, from relatively still hot air and the heated metal components that compose the grill (not to mention conduction through the food itself). Each one of these modes of heat transfer provide a different aspect to the grilling process. Radiation causes the sear, conduction is responsible for the grill marks and convection is responsible for the even heating and temperature of the food.
A deeper understanding of any process can lead to better results and engineering gives perspective into many of these processes. As far as grilling goes most of it can be picked up from experiences, but isn’t it more fun to know why these things happen! Happy Father’s Day to all the dads out there, no matter who does the grilling!
Olive trees. Photo Credit: bymovement.com
Note: Due to miscommunication, this post was submitted late and thus scheduled late; rest assured, regular scheduling will resume on Sunday.
Back at my parent’s house in North County San Diego we have a lot of olive trees and every year they drop their fruit on the ground and make quite a mess. There is no sense in letting all of these olives go to waste so I looked into ways to turn them into a usable oil. It was surprisingly simple, just follow a few steps.
First the harvest. The olives are pretty small and there are a lot of them all over the tree making it way too labor intensive to pick by hand. The simplest way to do it is to lay a tarp on the ground, get a ladder and comb the branches with a garden fork or rake. Let the olives and leaves fall on the tarp then collect them all and pick the olives out.
Now that you’ve got a good amount of olives you’ve got to get the oil out of them. This is where industrial manufacturers use massive hammer mills and centrifuges. That’s a bit of an overkill for home production. First you need to crush the olives, to do this you can just get a strong bag, fill it with olives and go at it with a hammer. I tried a meat grinder and it worked OK but the pits jammed up the machine, a bag and hammer wont have that problem!
Once you have a pretty good pulp of olives you’ve got to mix them so that the oil can form large enough droplets to be pressed out. Don’t mix for much longer than 15 min because you’re adding oxygen to the oil and that will give it an undesirable flavor and color, but if you mix much less than that the oil won’t form large enough droplets.
Now for the pressing. It takes quite a lot of pressure to get the most out of this olive paste so I got a 20 ton bottle jack for a car, built a frame with a two plates and used the jack to press the olives. First spread the paste on burlap or cheese cloth, really any porous fabric that will allow the solids to stay in place and the liquids to flow. Then fold up the cloth, put it in the press and press. Collect all the liquid that comes out and pour it into bottles.
The liquid in the bottles will be about 90% water and 10% olive oil. Leave these bottles in a cool dark place for several weeks to give the oil plenty of time to settle out then pour off the oil on top and store for later, or enjoy now. It will taste very different from store bought oil, in a great way!