AGA Electronic Gas Control

The article below comes from Eddie Boyes and has been requested several times since Eddie posted a comment on this site.  What Eddie has come up with is a way to control temperature of the AGA by controlling the gas flow through electronic valve controls (solenoids) and electronic sensors.  He applied this to the gas supply of his AGA that has a Teddington Mk 1 burner which uses mechanical valves and sensors that tend become faulty and unreliable over time.  By controlling the gas supply he is able to better control the temperature of the oven. He went a further step and added a timer so that the cooker basically cycles down overnight and cranks back up in the early morning to be ready for breakfast.

Eddie adds the following comments to the article:

Two points I would mention (corollary to the article).  The text ends by suggesting that I keep the top oven temperature at around 240C.  In fact, in reality, we tend to use a temperature between 180-220 depending on cooking needs,  The controller picks up the desired temperature perfectly – and reasonably quickly.

Secondly, of course, because the restriction is in the main supply to the AGA, you can’t restrict it too much – else the pilot will go out. and this limits the lowest temperature you can dial up.  I suspect that I could restrict mine a little more, but my current setting means that the lowest (top oven) temperature that I can dial up is about 140C (and the this is the eventual overnight temperature).

We are providing this article as an example of creative engineering. I give Eddie full credit for this article and I thank him for sharing it with us.  I must add that AGABloga and its operators reminds everyone that gas is dangerous.  Please do not attempt this modification yourself.  Any modifications made to your gas supply, burner and cooker should be done by a professional and could void your warranty.  AGABloga and Eddie Boyes are not responsible for any damage that may occur from the modification of your gas supply or cooker.

Gas Aga
Control (Mk 1)

(an electronic solution)

house
Markland Lodge

This article describes an electronic solution to the control of a Mark 1 Gas Aga (3-door, 2-oven), allowing the temperature of the hot oven to be monitored, adjusted and stabilised as required. It may well be useful for other models of Gas Aga also.

Background

When I moved into my house (Markland Lodge, Huyton), it had a 1970s gas Aga (Mk1). I confess that it has always been difficult to regulate the temperature. Even Aga engineers who have looteddingtonked at it seemed to have left it worse off than they found it. I realised last year (2013) that it was the Teddington gas valve that was faulty: the thermocouple sensor had become detached from the ‘cable’. I decided to buy a new valve and thermocouple (see picture) which cost me £150 including VAT (2013). It was duly fitted – with the original bypass screw, as recommended.

In order to test how well it was working, I not only threaded the new thermostat lead of the Teddington valve from the hot (top) oven to the burner assembly, but also took a digital thermometer lead – so that the temperature of the top of the hot oven could be accurately monitored. From early measurements with the thermometer, I noted that the top of the hot oven is about 25-30C hotter than the bottom of it – something that is probably already well known amongst Aga aficionados.

Even after much adjustment of the Teddington valve, however, I was disappointed that control of the Aga could not really be maintained by it – at least not as well as I would have expected. The setting-up process involves adjusting a very small ‘screw’ on the Teddington valve (inaccessible without taking the burner out) so that the valve opening/closing comes into play in the range of the outer dial (1 to 5). Even getting this right – after multiple extractions of a ‘hot’ burner assembly – it still didn’t really give the predictable setting of temperature that one might have expected. I decided that there had to be a better way – perhaps with the use of electronics.

What follows is a method of doing just that – in a system where the Teddington valve is more or less inoperative. In other words, the Teddington valve is fully open and not trying to restrict the gas flow to the burner in any way.

Controlling the Gas Flow

A solenoid gas valve would, I thought, allow me to switch on and off the gas to the Aga, but I couldn’t really see a way of siting it near the burner assembly in the supply to the burner. Also, if I put the solenoid valve in the main gas supply, it would have the effect of switching off the pilot light. However, I thought, what if I simply set up a system where, some distance from the Aga, the incoming gas supply is, under normal circumstances, restricted, and then I use a solenoid valve to by-pass the restriction? Provided I had a ‘robust’ pilot light, which remained lit whether the gas supply was restricted or not, then perhaps I could organise a degree of programming around this.

To test the feasibility, I decided to ignore temperature control (for the moment) and simply ‘lower’ the Aga temperature overnight using a solenoid valve connected to a timer. This would have the added benefit of saving money overnight. The situation for the gas input is shown here:

gaslayout

The gas enters though the ‘main gas stopcock’ at the top right. From there, it has three ways it can go to the Aga. If the ‘restriction by-pass valve’ is open, then this bypasses the other two routes, and the Aga works normally. If, however, the by-pass valve is closed (which I will call ‘normal operation’), the gas either goes ‘down’ through the restriction or ‘down’ through the solenoid valve. If the solenoid valve is ‘off’ (closed), then the gas is restricted and the Aga flame is low (pilot still lit). If the solenoid is ‘on’ (open), then the gas can flow freely to the Aga, and the flame will be full on. For this test, the timer was set so that the solenoid valve closed at 8 pm at night, and opened at 4 am in the morning.

It turned out that the pilot light was indeed robust enough to cope with the reduced gas flow through the restriction that I had made, and the Aga temperature dropped accordingly overnight. You can see from the wiring on the above photograph that the solenoid (at this stage) was controlled only by the timer. It is therefore possible to set the timer so that it restricts the gas flow for a given period overnight, and turns it up again for daytime use. Of course there is a great deal of hysteresis in the system because of the high thermal capacity and insulation of the Aga but if, as mentioned above, the gas is restricted between the hours of 8 pm and 4 am, the graph of temperature (top of the top oven) against time looks as shown in the graph immediately below. Here, temperatures have been taken over a few days, so there may be differences between adjacent points (as the oven is used differently on each day). Also, this graph applies to a particular setting of the ‘restriction’.

timedgraph

At 4 am (start of graph) the solenoid opens and the temperature rises. By around 8 am, the temperature is near to 260C – and still rising. It remains high all day until the solenoid is switched off by the timer at 8 pm, at which point it falls overnight. Notice that the maximum daytime temperature (around 280C) is rather high. Indeed, this was the reason for investigating this system; the Teddington valve could not be relied upon to work effectively in controlling this temperature.

Controlling the Temperature

What I really wanted to do, therefore, was to ‘control’ the temperature of the Aga. I decided to do this by starting with the solenoid/timer system above, and adding to it a ‘PID’ controller and a K-type thermocouple. Now, strictly speaking in what is described below, the ‘PID’ nature of the controller (Proportional, Integral and Differential) will not be used – I shall use only the simple relay output of the ‘PID’ (to switch on and off the solenoid).

I threaded a K-type thermocouple with a long (5m) ‘sheathed’ lead through from the top of the hot oven (where it was ‘fixed’) down to the burner assembly. The thermocouple lead was then taken to the outside world, and on to the controller, via the bottom left hand corner of the burner door, and around the side (photograph below shows this). This is a little unsightly. I had considered drilling through the side of the Aga, but thought better of this for now.

The thermocouple lead was taken to the ‘PID’ controller, which was sited some distance from the Aga (still in view in the kitchen). The positioning of the controller was such that the temperatures could be read clearly (once again, this can be seen in the photograph below). I say ‘temperatures’ (plural) because the controller shows the temperature you desire to set the Aga at (SV – in green) and the temperature it is actually at (PV – in red) at any particular time. The temperatures can be shown in Centigrade or Fahrenheit.

By putting the (normally closed) relay output of the ‘PID’ controller in series with the output of the timer to the solenoid (not shown in the photograph above), it means that, during the day (when the timer is ‘on’), if the temperature of the Aga (PV-red) is below the set temperature (SV-green), it will hold the solenoid valve ‘on’ (open) and the Aga will warm up. Once the set temperature is reached, it will turn the gas off (or rather, allow only the restricted flow), and the temperature will start to fall. The ‘PID’ controller also has an indicator light showing when the relay is open/closed.

‘PID’ controllers of this type have a number of settings that can be adjusted. You set the SV (desired temperature when the solenoid will switch off), and you also set a number of other parameters, one of which is the drop in temperature from SV at which it should switch the gas (solenoid) on again.

The following graph shows temperature against time for a number of particular settings. These are:
1)    A particular restriction/valve setting
2)    SV = 250 (degrees C)
3)    Drop in temperature = 10 (degrees C, before switching back on)

stabgraph

The temperature scale is different to the previous graph (140-260 degC), but the time scale is the same (4 am to 4 am).

You should be able to see that the controller does exactly what I wanted; the temperature during the day is maintained at around 244C on average – but I could change this by adjusting the controller SV.

Note that readings for the above graph were taken over a number of days, and this ‘masks’ the fact that the rather ‘random’ points along the ‘flat top’ of the graph are actually oscillatory – as the Aga heats up (solenoid open) and cools down (solenoid closed). The period of oscillation is almost 3 hours. On this test, the maximum value of temperature was 251C and the minimum is 235C.

aga

Photograph showing the ‘PID’ controller (top) and the exit point of the thermocouple lead (bottom)

Two other things should be noted. The solenoid definitely did close at 250C, but there was obviously ‘heat flow’ in the system which took the maximum up to 251C. Similarly, the solenoid definitely did open at 240C (250-10), but the Aga continued to cool to 235C (even though the gas was on full) before it began warming up. It is well known that there is a good deal of hysteresis in the system. A smaller value than 10C would perhaps help to reduce the amplitude of variation (and time period), but the hysteresis of the system will inevitably mean it cannot be eliminated.

Also, it is clear that if the Aga were being used a lot for cooking, it is likely that the minimum temperature of the above graph would go even lower than 235C at different times of the day. The very ‘nature’ of an Aga is such that you cannot really ‘control’ the temperature so that it is entirely stable. However, when the temperature does go very low for some reason, the gas would be on full (solenoid open).

I shall continue to experiment with various settings (restriction setting, SV temperature and temperature ‘drop’ etc) until I find the results I want. However, I am now confident that I can control the Aga (inasmuch as it is ‘controllable’), and the whole thing has cost me less than the £150 that I paid for the Teddington valve. I also have a clear indication in my kitchen of what the Aga is doing and what the temperature of the top of the hot oven is.

Eddie Boyes, January 2014

PS: After further experimentation, I have settled upon,

1)    A particular restriction/valve setting
2)    SV = 240 (degrees C)
3)    Drop in temperature = 2 (degrees C, before switching back on)

This gives (assuming no cooking) an oscillation period of about 1 hr 15 min, and a variation in temperature of about 6C, with a mean of about 238C. The following shows a simulation of the daily changes in temperature (assuming no cooking) when the timer is set at 8pm (off) and 4am (on):

stabgraph2

 

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AGA Pulled Pork BBQ

The AGA makes a great pulled pork.  The process is simple:  brine, rub, slow cook.  The recipe takes some planning due to the long brine and cooking times so plan ahead. It brines for 12-36 hours and slow cooks approximately 1.5 hours per pound – basically all day (or night). The Boston butt (pork shoulder) used in the post is 6 pounds.

First you make the dry rub:

  • 1 tbsp each of paprika, cumin, cayenne pepper, chili powder, garlic powder, salt, black pepper
  • 1/2 cup brown sugar

Mix the ingredients and set aside. If you have smoked salt or smoked paprika, use it.

 

Brine:

Make the brine by adding 1/2 cup of salt to 2 quarts cold water. Stir until dissolved. Mix in 1/2 cup brown sugar and 3 tbsp of the dry rub.  Wash and dry the pork and place into 2 gallon zip lock bag. Pour over brine, seal bag and put into refrigerator for 12 to 36 hours.

 

Rub the Pork:

After the brine, pat the butt dry and and place in the small roasting tin lined with foil.  If you are using a larger joint that is too big for the small tin then stick it in the Le Cruset dutch oven you got for Christmas last year.

Rub the butt with all of the dry rub mix.  Place in tin with the fat cap side up. This will slowly baste the joint during the long slow cook.

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Slow cook:

Insert your digital remote meat thermometer into the joint but not close to the bone. Place the prepared butt in the simmer oven, uncovered.  Cook until the internal temperature is 200F (93C).  Plan on approximately 1.5 to 2 hrs per pound. This 6 pound butt took 6:15 to cook.

IMG_9363

After the internal temperature has been reached, pull the tin out of the oven and place on top of simmer plate cover to rest.  Cover with foil and let rest until temperature has dropped to 170F (77C). It will take approximately 2 hours to rest. This 6 pound butt took 1 hour to reach 170F, uncovered on top of the simmer plate cover.

Pull the pork:

To pull the pork, remove the crusty fat cap and start pulling apart the meat. Use forks or salad tongs or kitchen tongs.

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Enjoy the fruits of your labors:

Mix in your favorite sauce or make your own such as Carolina vinegar based sauce, South Carolina mustard based sauce,  or the ketchup based red sauce.  Enjoy in a sandwich or as a dinner with a side of cole slaw and mac and cheese.

 

 

 

AGA Dutch Apple Pancake

  

  This is a great recipe for the AGA and fairly quick. I followed the Dutch Baby Pancake recipe from Bon Appetite. It took exactly 15 minutes to bake on the 2nd set of runners in the roasting oven. The recipe said to heat the skillet in the oven for 8-10 minutes after sautéing the apples. I heated it for 2 minutes then plopped it on the boiling plate. It worked fine.  

Guten appetite! 

 

Image

Jamie Oliver’s AGA

Jamie Oliver's AGAJamie Oliver on Instagram

Fajitas in the AGA technique 

  

 I wanted to share this technique for cooking fajitas in the AGA. It turned out really well. 

Ingredients- typical tex mex stuff:  green , yellow and/or red bell peppers, red onion, 2 chicken breasts, soft tortillas; sauce- mojo criollo; spices- cumin, chili powder, coriander; condiments- cilantro, sour cream, salsa, limes, guacamole.  2 peppers, 2 med. onions and 2 chicken breasts is enough to feed 3 hungry gringos. 

First thing is to tear off a 2 foot piece of foil, lay tortillas on one side and fold it over and crimp the seams to make a sealed pouch.  Toss it in the simmer oven to warm. 

Wash and pat dry the chicken. Slice crossways or lengthwise about 1/4 inch thick. Place in small roasting pan with a generous amount of mojo criollo, enough so it almost covers chicken. Toss the chicken around a little and let it sit and marinade.

Next slice the onions and peppers lengthwise to make slivers. Place in bowl and pour in a few glugs of olive oil. Add roughly 2 teaspoons of each of the spices. Quarter a lime and squeeze it over the veggies. Toss to coat and add the squeezed lime skin to the bowl. 

Take your 10″ iron skillet and place it on the boiling plate. Put in a glug of oil. Let heat for a few seconds until shimmering and almost smoking. Add the onion and pepper mixture (include limes!). Stir for a minute then pop in the roasting oven on the floor. 

Put the chick on the first runner of the roasting oven. 

After a few minutes pull the skillet out onto boiling plate and stir for 30 seconds then back in the roasting oven floor. 

The onions and peppers should be done after about 8-10 minutes total. Transfer to a serving plate and put skillet on a pad on the dome of the boiling plate. Don’t clean it. Discard cooked limes. 

Put the chicken out of oven after about 12 minutes total time (could take a little longer). Using tongs to transfer pieces to the skillet and toss to coat with all of that goodness in the skillet. Use skillet as serving dish. 

Pull the tortillas out and open pouch. Be careful of the steam! 

Assemble fajitas, buffet style, by filling the tortillas with onions, peppers, chicken, and your condiments- sour cream, cilantro, guacamole, squeeze a lime wedge.  Serve with salsa on the side. 

This is fairly quick and easy without a lot of mess and sooooo good! 

Enjoy! 

AGA Pork Ribs

IMG_0213
Pork ribs (either baby back or St. Louis style) are super easy in the AGA. The steady temperature of the AGA cooks a really nice rack with minimal fuss. Based on other posts I read on the WWW, I concluded it would take 2 hours in the simmer oven on the 2-oven AGA. This was WAY OFF! I found that a rack of room temperature ribs takes 4 hours. Here are the details of the process:

Of course, prep ribs by rinsing and pat dry and remove the membrane on the non-meat side
Make dry rub: 1/2 cup brown sugar and various amounts of the following (whatever you have): smoked salt or salt, ground pepper, cayenne, chili powder, garlic powder, mustard powder, paprika, thyme, tarragon.
Rub it in
Line deep roasting tin with foil
Place roasting rack in raised position
Put ribs on top, you may have to slice in half and arrange as shown in photo
Put in middle of simmer oven 2nd or 3rd runner.
Roast for 2 hours
Rotate tin and roast for another 2 hours but start checking for doneness after 1 hour by the bend test
You can add a little crispness to them by letting them spend 15-30 minutes on 1st runner in the roasting oven.
Let them rest for 30 minutes- I like to wrap in foil and towels and rest for an hour.
Slice and serve
Note that ribs should not fall off the bone. The should be tender and tear easily from the bone.

Enjoy!

Clams Casino in the AGA

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We went clamming the other day and came back with a good sized harvest. The smaller ones were set aside for a pasta dish. For the larger ones, we made clams casino.

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Shucking the clams can take a while until you get a system down. Our clams were not relaxed so I used an oyster knife to pry open the hinge a bit until I could slide the clam knife in on the opening side.

The concept is simple: sauté some delicious ingredients and make a stuffing to put on top of clams on the half shell. It contains bacon…need I say more?

Ingredients
12 cherrystone clams, cleaned and shucked, bottom shells reserved
Rock salt or coarse kosher salt (for stabilizing the clams)
3 slices of bacon
Couple of glugs olive oil
Thick pad of butter
1 garlic clove, minced
1 shallot, minced (optional)
Small yellow onion, finely diced
Half of green pepper, finely diced (optional)
Salt and freshly ground black pepper, to taste
½ teaspoon dried oregano
½ cup dry white wine
½ cup panko (Japanese bread crumbs)
¼ cup grated Parmesan cheese
1 tablespoon minced fresh herbs (oregano and basil) (optional)

Preparation

Shuck the clams, reserving the bottom shells. Arrange them on a bed of rock/coarse salt on a the small roasting sheet.

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In a 10 inch sauté pan, cook bacon on 1st runner of roasting oven (or as high as your pan will allow) for 7-8 minutes until crisp. Remove from pan, drain on paper towels and crumble; set aside.

Wipe out the sauté pan, but don’t wash it. Keep the pan hot on simmer plate Heat the pan hot on simmer plate and add the olive oil and butter. Heat until butter melts.

Sauté, on the floor of the roasting oven, the garlic, onion, shallot and peppers with the oregano and a pinch of salt and pepper until softened – about 5 minutes.

Return to simmer plate and add the wine. Reduce the pan liquid to about half.

Stir in the panko, reserved bacon, fresh herbs and half the Parmesan cheese. Taste and correct seasonings.

Divide the stuffing equally among the clams, mounding it up slightly. Sprinkle the rest of the Parmesan evenly over the stuffing.

Bake on the 1st runners of the roasting oven until the clams are cooked and the topping is deep golden brown, about 8- 10 minutes.

Serve immediately.

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