Dave 123
Legendary Member
- Location
- Cambridgeshire alps
Bbq vents
- Thread starter Markymark
- Start date
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Sadly I couldn't prevent the proles from answering. I mean, FFS even you got to post.
Yellow Saddle
Guru
- Location
- Loch side.
I take it your chef only cooked on an electric stove or you never venture into the lower regions of House MarkyMark, so you may not have picked up some of the finer nuances of cooking on combustible material. Thing is, combustibles need oxygen. The lower vents supplies oxygen to the glowing charcoal. That glow is heat as a by-product when the pure carbon in the charcoal combines with oxygen to form carbon di-oxide. One carbon molecule combines with to oxygen molecules and the oxygen can only enter from outside the BBQ. These vents have to be underneath the charcoal because hot air (in this case, hot CO2 and some air) rises fast to the top of the BBQ and if the vents were above the charcoal, the oxygen would never get to the charcoal.
If the lid was off, the hot air just escapes into the atmosphere and the only heat cooking your fillet would be radiated heat (infrared light) directly from the coals. This would only reach the underside of the meat. Radiation is only in line of sight.
If you put the lid on, the hot air fills the cavity and cooks the meat from all sides. However, the air must escape otherwise the chamber is filled with only CO2 which would kill the fire. They make fire extinguishers from CO2, after all. Therefore you have to open a little vent on top.
So, oxygen is sucked in from below and CO2 is pumped out the top. The meat sits in the hot air draft and gets cooked all over.
Next lesson will be on why keeping champagne outside next to the BBQ in ice water keeps it cooler than plonking it in a bucket of ice cubes. Let me know when that crisis arises.
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Yellow Saddle
Guru
- Location
- Loch side.
Thicker cuts of meat requires different treatment from say slices of steak. A streak can be cooked on pure radiation (heat supplied from the underside) because the radiated heat will penetrate say, 6mm into the meat before the outside layer is scorched black. Then you turn it over and do the other side, giving you 12mm off cookedness - which is enough to make the steak eatable without dripping blood. If the meat is 100mm thick, the radiated heat will still only penetrate 6mm per side before the outside is completely black. This leaves you with 88mm of uncooked heat.
Now, if you close the lid, the combustion is slower but the heat circulates around the meat (there is come convection and turbulence inside the dome lid before the heat eventually escapes through the top vent, just like in an oven). The lower heat from all sides gives the heat time to penetrate inside the meat without scorching the outside. Remember, meat is a heat insulator and heat travels slowly through it. The lower the heat, the better it will penetrate over time giving a more even cook. By closing the lid you are restricting combustion and the temperature reaching the meat is lower than by pure radiation when the coals are really fired from a free supply of oxygen.
Thus the rule of thumb is: For thin cuts, flash grill it in an open kettle. For thick cuts, close the lid for a more even but slower cook. Chicken requires the latter because chicken meat is very dense and an excellent insulator. It can therefore almost never be cooked on a grill alone without really searing the outside. Jut biting into a chicken breast will confirm its density. It can be grilled if you say slice the breast into two thinner "steaks."
Now, about that Lambrini. always thought it was a car, but anyway. If you have a bucket of ice water (i.e. lots of ice cubes and lots of water) as apposed to just a bucket of ice, your Lambor...Lambrini will go colder quicker and reach a lower temperature. This is for two reasons. When it is plonked into a bucket of ice cubes, on a few points of contact between ice and bottle is made. The cubes by definition cannot embrace the bottle. It can only touch it here and there. Ice water on the other hand, completely embraces the bottle, more contact is made and more heat travels from the bottle into the ice, making the bottle colder.
Further, and this is the strange one to non-chemists, ice water is colder than ice. In other words, if you put ice into water, the resulting slush will be colder than the ice itself. This is because energy is required to break up the ice's structure - which is what happens when it melts - and that energy is sucked from outside the ice, making the water colder than the ice itself. The converse, when water is frozen to become ice, is also true.
Next lesson - how to start the lawnmower so you can BBQ and sip Lambrini on a perfect lawn even when the chef and gardener is on vacation.
Ok, thank you. I get the open/closed lid difference. What I mean is if you close the lid why have vents if they are needed to be open? If they control the temp, which I guess they do, in what sequence do I close/open then to control the temperature?
Ps my wife tends to deal with the gardener. He's always around when I'm at work and she's constantly down in his shed. Not sure how good he is though as not much gardening ever seems to get done.
Ps my wife tends to deal with the gardener. He's always around when I'm at work and she's constantly down in his shed. Not sure how good he is though as not much gardening ever seems to get done.
Yellow Saddle
Guru
- Location
- Loch side.
There are several "venting" scenarios".
1) If there were no vents at all when the lid was closed, then the combustion in the coals would die down and the heat would fade away. The only heat available to cook would be residual heat inside the charcoal and metal of the BBQ. This isn't much and the cooking would decelerate quickly and then stop. You could use this at the end of your cook to keep the food warm, for instance. Or, to dramatically slow down cooking when you've discovered that you've run out of Lambrini and the driver has to rush off and get some. You may be able to restart the process by opening everything and fanning the coals. Fanning them would not cool them (much) but supply huge amounts of oxygen that will get them going again. You could use this setting to kill the combustion after cooking so that you could re-use the remaining charcoal. However, I doubt that the unit will seal tight enough to arrest combustion. Combustion is a bitch, once it gets going it goes. Even when oxygen is restricted, it will still combust but simply produce carbon monoxide, which is a less efficient process but can get away with just one unit of oxygen whereas before it required two.
2) If you close the lid and only keep the bottom vent open, then, depending on the design and how tight the lid closes, the fire could asphyxiate itself with its own CO2. I don't do any cooking myself so I can't say exactly how this will pan out in the real world, but I would guess that you will have maximum heat surrounding the meat for a short time.
3) If the lid is closed and top and bottom vents are open. Then you will have less heat inside the dome since much of it will escape out the top after swirling around inside but you will have the benefit of completely exhausting the charcoal which will give you longer cooking time. This will be better for thicker cuts that require slow roasting.
I am told that some of these contraptions have thermometers. Depending on how they are placed, these may confirm my guesses. I guess that the vents are really airtight and that the amount of heat lost through the thin sides of the steel dome negates most of the post-rationalized science of vent placement and sequencing.
subaqua
What’s the point
- Location
- Leytonstone
just don't use a scuba cylinder with 100% oxygen in and some lighter fluid to make a simple ramjet. the neighbours will get mightily upset with the noise . it moved 6ft across the garden fairly sharpish.
my 7 yr old son loved it however.
Vernon liked the idea when i posted about it previously
my 7 yr old son loved it however.
Vernon liked the idea when i posted about it previously
hopless500
Trundling along
- Location
- not-as-flat-as-you-think Norfolk
Or what you used to have before you paid it off
Oh yes, but being in the North(ish) I only paid £3.75 for my house.Or what you used to have before you paid it off
.... and the mask slips...
Yellow Saddle
Guru
- Location
- Loch side.
I won't misread it as a slip at all. I think he's feeling a bit soft on this here Monday and is just trying to reach out to the great unwashed up north. He'll come to his senses again come Tuesday.
coffeejo
Ælfrēd
- Location
- West Somerset
It might have been a bet or a dare?