August 24, 2010 - 1:01am
Silver specks on crust
I have just acquired a used industrial oven and started baking in it over the weekend. It was pretty dirty inside and had to use of lot of chemical cleaner (It is 17 years old and seen a lot of use - not exclusively bread).
After baking a few loaves, I've noticed that the exposed crust is covered with silver specks (couldn't photograph it - they are small), something like glitter. The baking paper was dusted liberally with a slightly coarse semolina flour.
I cleaned the oven thoroughly and let it air. I then warmed the oven at about 200C for an hour before using it, followed by another airing.
I haven't noticed this effect with my standard kitchen oven.
Any ideas?
Joss
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If the oven is a fan-assisted or convection model, there may be some metal parts rubbing together and creating tiny metal particles that are then blown about in the oven until they settle on on surface (such as your bread's crust). I would expect that you would be hearing some sort of whining / squealing / squeaking / tapping sound if that is the case.
I'm not sure what else would lead to the creation and deposition of particles that small in an oven without a fan. Something has to be propelling them from their point of origin to your bread. Do the door hinges need to be lubricated? Are you seeing particles on horizontal surfaces in the oven, like the racks or the floor? Can you stick a baking sheet or baking stone in the oven that would have a high enough contrast with the particles so that they show up readily? If so, you could start a series of checks to find out which oven conditions (on, off, hot, cold, fan, no fan, etc.) result in particle deposition. That would at least give you a hint about where to look for the source. You may then need to call a service technician for a final diagnosis and repair, should that be required.
Paul
Thanks Paul for your suggestions. Last night I gave the oven another wipe down and ran some tests. There is no fan, it is heated from all 4 sides. The walls are galvanised, but are damaged due to long (and not careful) use. There are numerous places where the underlying metal surface is visible, and scratching it can produce the metal specks.
I ran the oven for 20 minutes with just the tray and afterwards there was a good amount of metal "debris".
Now for the solution... My girlfriend has suggested either waiting for the fresh metal surface to oxidise or to paint it with the kind of paint you would use on a metal fireplace. Not sure if these solutions are ok yet.
Once again, thanks for the advice, and I'll keep you posted to the final solution.
Joss
An oven with galvanized interior surfaces--that's a new one for me! The underlying surface is probably a mild carbon steel that would be susceptible to corrosion at the higher temperatures of an operating oven, particularly with the humidity that comes from the baked goods; not to mention steaming.
I think that we have a metallurgist or two in the TFL community, so they will be much better equipped to respond than am I. From my limited knowledge, I would speculate that the zinc layer is debonding from the underlying steel. Still guessing, I suspect that the most likely sources are the areas that have been scratched or gouged. And I really have no idea what to suggest to cure the problem.
Regarding paint: go carefully. You first would need a paint that will bond with the zinc. It would also have to be able to handle the high temperatures and the cyclical heating and cooling swings that occur with normal oven operation. Finally, it would have to be rated as safe for use in food preparation. Most high-temperature paints I'm acquainted with are for external use, not for use on the interior surfaces of ovens. Most paints that would bond with zinc (and zinc-rich primers) that I have seen have been for use on automobiles - not ovens. If you can find something that would be suitable for all of the conditions, it will probably cost more for a quart than you paid for the oven itself.
Sorry not to have something more positive to share. I don't know that you are at a dead end. I do know that you need to talk to someone, maybe a manufacturer's rep or repair tech, who has more useful information than I possess.
Best of luck.
Paul
Hi Paul,
My girlfriend has priomised to call the manufacturer for me. We live in Hungary, and as she is both Hungarian and an engineer she's much better equipped at handling these technical situations.
She told me the oven is "horgányzott" which I translated as "galvanised". I may have got something wrong of course.
I know that the internal part of the oven is replaceable, but it will cost about half the price paid for the whole oven. I'm optimistic that we'll get it in working order though. It also has 2 sections, so far I've only tried (and cleaned) the upper section.
I just have one picture of the oven from a distance (it was a suprise present hence the red bow). I'll post some more useful pictures later.
http://www.flickr.com/photos/18173822@N05/4844091307/in/set-72157624493110067/
Thanks again for the advice and information.