Roller Grill PZ330 Electric Pizza Oven

[Marco Polo]

I own the Roller Grill PZ330 electric pizza oven.  I have had it now for about 4 years.  I am based in the UK and paid about £390 for it.  It’s a lot more expensive now though, maybe an extra £100.  It has a pizza stone surface and uses a normal domestic plug and is small enough to fit snugly on any countertop.  I was making ok “nearly-Neapolitan” style pizzas and getting temperatures of 360ish degrees Centigrade (680ish Fahrenheit) in my oven.  However, as a true Neapolitan pizza aficionado I wanted to find some way of increasing the temperatures in my oven. 

While on ebay, I stumbled upon a pizza oven thermostat for £38.00 that would reach 500c (932f).  I immediately purchased it not really knowing if it would fit into my oven.  Anyway, when it arrived I immediately removed the outer cover of my oven to check the dimensions of the installed thermostat and they looked exactly the same.  So I began by carefully removing the old thermostat and probe and carefully replaced it with the new 500c degree thermostat and probe.  Everything fitted perfectly.  I was initially concerned about the probe as it was a little bigger but even that fitted perfectly.  I switched on the oven and was half expecting a large explosion.  I have to say at this point that I am not a qualified electrician nor expert on electronics but what I did do is carefully checked where everything went and took my time.  Anyway I was still a little concerned that I might have done something wrong.  I switched it on and everything seemed to be fine.  As the temperature rose I began to smell burning rubber, so switched it off immediately and removed the cover when cooled.  There was a small burnt rubber seal connected to the external oven cavity, which didn’t seem important.   I removed it and switched it on again and have since had no problems.  I have one of those temperature guns.  At its maximum setting I am getting surface temperatures of 540c (1004.0f).  More than enough to cook a Neopolitan pizza. 

My pizza making attempts weren’t that bad but I soon discovered that the surface temperature was a lot hotter than the temperature above the pizza, so I am getting fantastic charring on the bottom of the pizza but I am failing to get that characteristic leoparding on the crust.  With conventional wood-fire ovens there is normally plenty of room above the pizza which I think causes a convection type movement of air and I think this is why the temperature above is exactly the same as the surface temperature.  My electric oven is very small and there is simply not enough room above the pizza to create the convection temperature needed for leoparding.  My cooking times were 3.5mins and now they are 2ish minutes. 

I am in the process of experimenting with installing fans in my oven to circulate the air more evenly. 

Anyone need pictures or any information on installing the thermostat don't hesitate to contact me.


Below is a link to another topic which has some pictures of Pizzas cooked in my Roller Grill:

http://www.pizzamaking.com/forum/index.php/topic,10898.msg97468.html#msg97468

[Tampa]

I love the fans idea.  It seems that the key is to mount the fan blade like a propeller on an inboard boat - the motor and bearing are in a dry/cool area and the prop is in the heat.  Or you could do it the easy way and buy one from a convection oven, maybe on ebay.

I did a quick google image search on your PZ330.  It looks like there are separate heating elements for the top and bottom.  I'm a little more gamey than some and would be tempted to put the upper element on a simple toggle switch - when it's on, it's on.  Also, given that you have a lot of stone mass (i think), you can probably turn off the bottom stone when you throw the pie.  I've been doing that at 700F lately, and there is plenty of latent heat to cook the bottom in 3-5 minutes while the top is IR cooking.

Dave

[Marco Polo]

I'm a little more gamey than some and would be tempted to put the upper element on a simple toggle switch - when it's on, it's on.  Also, given that you have a lot of stone mass (i think), you can probably turn off the bottom stone when you throw the pie.  I've been doing that at 700F lately, and there is plenty of latent heat to cook the bottom in 3-5 minutes while the top is IR cooking.

Dave

Hi Dave, that’s a good idea.  But I am really keen to get my cooking times down to 90 seconds.  I think that is the sweet spot.  At the moment I can’t really achieve this as the bottom cooks and chars perfectly but the top is underdone.

I think the way forward is to go with the fans. 

But I am not sure though how I should approach this. 

There are two possible ways I could do this:

1.   Like you stated I could mount the fan motor and bearing outside the oven cavity and the blade inside the oven right at the back.

2.   Or...I could drill lots of very small holes into the aluminum just above the top heating elements, have a fan mounted on the outside funnelling air into the cavity of the aluminum thereby forcing air in a downward motion through the holes towards the pizza.


I am most interested in the second idea as it allows me to have some kind of contraption on the outside to control the volume of airflow.

Let me know what you think.

Below is a picture of the inside of my oven to illustrate.


Jason.

[Tampa]

Whenever possible, I'm a "do no harm" guy - meaning test the idea somehow before you cut.  Do you know that you have 2 heating elements?  If so, then I think you are "in the money".  I've played with my buddy's cecilware electric a bit and know he has top and bottom heaters.

I'm a big fan of individually controlled top/bottom heat.  You already have two thermostats and dial gages.  I'd consider running one on the bottom, and the other on the top.  Given your goal to be "done" in 90 seconds, all you need is a stone temperature that hits your target.  Say that is 850F, throw the pie, turn off the bottom burner and full on the top burner.  You'll probably need the top on about 1-2 minutes before you throw the pie as a "preheat".

I'm not an expert on electric ovens.  Frankly, my limited experience suggests they show wild temperature swings (lots of inertia in the thermostat - stays on or off too long).

[Marco Polo]

I'm not an expert on electric ovens.  Frankly, my limited experience suggests they show wild temperature swings (lots of inertia in the thermostat - stays on or off too long).

Yes, you are right.

With my new thermostat, I get readings well over 500c, sometimes up to 560c, then the switch kicks in.

I will try your idea first before performing open heart surgery on my oven:

1.  Get the surface temp up to 400-420.
2   Switch off the bottom element.
3   Turn up the thermostat to its maximum setting.
4   Wait maybe 5 minutes, then throw the pie in.


Jason.

[sear]

i dont think this is a good idea.
your oven was designed to get to a certain temp you are tricking it to draw even more current, the wiring of the oven and the wiring in your house may be heating more than its supposed to and could eventually melt and cause a fire.

this is not the same as people using the cleaning cycle to get higher temps, which is safer because the oven is designed to handle the stress of the high heat clean cycle.

 

[Marco Polo]

With the new 500c thermostat I have performed several stress tests on my oven at its maximum temperature setting lasting 60 minutes.  I haven't had any problems.  But I will take on board your comments.

[sear]

have you check the operating temp of the power cord, wall outlet ? and i would take the face off the wall outlet and check the temps of the wires on the outlet during use

[Marco Polo]

have you check the operating temp of the power cord, wall outlet ? and i would take the face off the wall outlet and check the temps of the wires on the outlet during use

How on earth do I do these checks with out blowing myself up?

The power cord connected to the oven is very very thick.  If there was a problem with wires overheating would I have not discovered it by now, considering I have done two stress tests lasting 60 minutes each?

Anyway I am sure that they make these ovens to operate above their recommended tolerances?

[sear]

use a non contact digital thermometer, like the ones everyone is using to check temps of their stones.

a couple of 60minute tests i dont believe are enough.

how long will a car run low on oil before the engine blows up ? same principal applies here, you dont know how much it can take before it gives up until its to late


also looks like that model is a 110V machine, correct ?
what is the circuit amperage rated for where its plugged in ? 

[Tampa]

I like the safety suggestion but think you are probably OK here.  Whatever the oven takes, if the circuit breaker doesn't pop (and your house wiring is "code"), the total amperage is below the trip point.  If you don't think your wiring is up to code, all bets are off.

When you first turn the oven on, the burner runs full out for at least 15 minutes before reaching cooking temperature.  You said the max temp before any modification was almost 700F.  Electrically, ramping the temperature up to 700F in 30 minutes is no different from running the circuit at any other temperature as the amperage through the line is the same.

Nearly all products are engineered with a safety factor.  I'd guess this has at least a 20% safety factor, probably a lot more, given the inaccurate thermostat they use.  Quick math suggests you are OK to 840F-ish.

We modified my buddy's cecilware to run much hotter, but his oven is outside.  I did take things apart to do the "tuning" and noticed that the insulation wasn't the greatest, but he is always around and really doesn't run the thing more than 750F (800F tops a time or two).

What we did find with his oven was that the stone temperature varied greatly as the areas right above the electrical heating element were something like 50F hotter than more remote areas.  I used metal lath (used for building construction) cut to the exact dimension as the pizza stone and used it as a 1/8" spacer under the stone and on top of the metal pan supporting the lower heating element to even out the heat.  It worked great and you might need this as well.

If this is a 110V, flimsy construction product, take more care.  I don't know this product.  If it is more of a commercial grade product, which the 700F seems to suggest, be careful, but you are probably OK, IMO.

Dave

[Tampa]

Update: I discussed Marco's situation with the owner of the modified Cecilware oven.  He reminded me that when we took the Cecilware apart to do the mod, there were some signs of melting plastic behind the back panel - before any mods were done.  In his case, the evidence of melting was located where the electrical connection was made between the power cord and the heating elements.  They use a black plastic/metal thumb nut for the electrical connection.  We did the modification knowing the risk because his oven is located outside and he is always in the area when the heat is on.  There have been no problems in 2x weekly use over about six months.  He usually cooks at 700F +/- 100F degrees due to temperature swings.

Marco, according to a recent post, you are running this oven at 450C (~850F).  I'd be tempted to take a look under the skin to see if there is anything irregular looking - especially if you use this oven inside.

Regarding the other stuff: household wiring, power cord wiring, heating element design, circuit breaker - I stand my my earlier comments.  If you can run it full-out for 30 minutes on warm up, it's been stressed already.

Dave

[Marco Polo]

I'd be tempted to take a look under the skin to see if there is anything irregular looking - especially if you use this oven inside.

Thanks Dave

Will do and I will continue to monitor the oven and report back anything irregular.


Jason.

[Marco Polo]

I'm a big fan of individually controlled top/bottom heat.  You already have two thermostats and dial gages.  I'd consider running one on the bottom, and the other on the top.  Given your goal to be "done" in 90 seconds, all you need is a stone temperature that hits your target.  Say that is 850F, throw the pie, turn off the bottom burner and full on the top burner. 

I did what you suggested dave and the results are much better.  Still cooking around 2ish minutes though but with this technique I am getting much better charring around the crust. 

For pics click on the link below:

http://www.pizzamaking.com/forum/index.php/topic,10898.new.html#new

[Tampa]

The pie looks great.

I suspect that your oven is somewhat similar to my friend's Cecilware.  In his setup, there is one electric element on the underside of the pizza stone, and a second electric element on the roof of the cooking area.  If so, and if the roof element is unobstructed (by sheet metal, etc) from the top of the pie, I'd suggest the following.  It's a poor-man's solution to modifying the grill.

Get the pizza stone to your steady state cooking temperature, say 850F, as measured by an infrared temperature gun (calibrated & accurate).  Once there, turn the thermostat up another 50 degrees or so - just enough so you know the burners are on.  In a minute or so, throw the pie.  Cook for 90 seconds and remove.

Here's the reasoning.  The pizza stone has a lot of thermal mass and having the burner on or off won't make a difference in the surface temperature in 90 seconds.  However, having the top burner on will radiate as much heat as possible in the 90 seconds - and I think you will need all of that heat.    You might have to do some experimenting to get the right top/bottom cooing.  I don't know how long it takes to get your heating element red hot, but I guessed a minute or so.  Turning up the thermostat earlier if you are not getting enough top cooking (and the bottom isn't too chaired).

Dave

[Marco Polo]

Hi Dave,

I think what I need to do is to experiment more with the surface temp.  When I cooked this pie the surface temp was about 420c, which I think is a little too high as the charring on the bottom was quite pronounced, still delicious though.  I think the reason for this is I turned up the upper thermostat and left it too long before I put the pie in, maybe five or so minutes, enough time to further raise the surface temperature beyond what is ideal.  Next time I will try and get the surface temp at around 400c, then immediately put the pie in and then raise the upper heating elements to maximum.  Cook for 90 seconds.  This will however require a little trial and error before I get it just right.

Anyway, regarding the modification of my oven.  I am pretty confident that it will not cause any problems.  I opened up my oven the other day and did a thorough check of all components and there was no sign of melting or anything irregular.  I also did another stress test and left the oven on at its maximum setting for about an hour and there were no problems.  I was getting a constant temperature of around 550c.  The Roller Grill is a pretty sturdy and well constructed piece of kit and is designed as a professional catering tool and not for the domestic market so I think its safety tolerances are very high.  I will still nonetheless monitor the situation.


Jason.

[Tampa]

Good plan.  Let us know when you get close to the right top/bottom combination.  I think you have a good chance of success.

Also be sure to measure various spots on the stone to make sure the temperature is relatively uniform.  My friend's oven varied by 50F or more - hotter directly above the heating element and cooler elsewhere (even in the middle where there was no element directly underneath).  A metal lath spacer helped even out the temperature.


Also, I've found some variation in the accuracy of IR guns from Sears and Harbor Freight.  Sears was off 50F, HF was off 20F.  If you can, check your setup against a trusted standard.

Dave

[anuradha]

While on ebay, I stumbled upon a pizza oven thermostat for £38.00 that would reach 500c (932f).

Is this the thermostat you got?

http://www.ebay.com/itm/140429433777

[Marco Polo]

Is this the thermostat you got?

http://www.ebay.com/itm/140429433777

Yes, that is the one.

[anuradha]

Yes, that is the one.

Thanks!