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  • matthanna
    started a topic Building a 42" oven mainly for bread

    Building a 42" oven mainly for bread

    Hi All,

    New user, first post, so please excuse me if I am doubling up on previous posts (I have tried searching).

    I've started building a 42" Pompeii Oven using the Pompeii Oven Plans Version 2.0. These instructions are awesome, but I am struggling to work out a small part regarding the hearth. My wife and I are big bread makers, and plan on making high volume breads with this oven along with pizza.

    On page 28 of the instructions, it show how you could add extra heat mass by sinking a brick island into the insulating layer. It says to take care not to reduce the your insulating layer to less than 3.5 inches.

    Does this mean that the hearth is comprised of the 3.5 inches of structural concrete, then a 3.5 inch insulating concrete layer, followed by the layer of firebricks that make up the extra heat mass under the cooking floor which could then be surrounded by normal concrete?

    I can't imagine that the extra firebricks being set into the 3.5 inch insulating layer would be safe, as it would only leave an inch or so of insulating concrete before the structural concrete layer. If I built the hearth layer as a 9.5 inch rather than 7.5 (being 3.5 structural concrete, 3.5 insulative concrete, 2.5 firebrick surrounded by either insulative or structural concrete) would it be a bad, unthinkable, or unrecommended configuration?

    Thanking you in advance!

    Matt


  • matthanna
    replied
    Thanks very much Mike

    Diet or not, I'll be eating plenty of food from this oven - looking so forward to it.

    Leave a comment:


  • SableSprings
    replied
    A black oven has the fire built in the cooking chamber. As the cooler, brick chamber is heated, the dome/chamber will turn black with soot. At about 600F, this soot (carbon) will burn off and the bricks clear (turn back to normal color with some clinging white ash powder). Often you hear or see "When the dome clears..." as an indication of the firebricks coming to temp. The term "black" oven simply refers to this type of oven and heat loading process. The ash & coals are removed and once the oven bricks have equalized their temperatures to desired temperatures, baking can commence. This type of oven is the most commonly done and relatively easy to construct (especially with all the resources here at the forum.

    A white oven, has a separate fire box from the cooking chamber. The classic commercial French & Spanish ovens of the late 1800's were mostly white ovens. The fire is started in a lower or side chamber (fire box) and a dual vent system allows the initial smoke to bypass the cooking chamber. When the oven chamber is to be heated, there is a vent connecting the fire box that's opened. The fire at that point should not be producing much in the way of smoke...it's primarily just a hot fire & coals. The heat is directed into the chamber, slowly bringing the chamber's firebricks up to temp. When the oven has reached the desired temp, the vent is closed and baking can commence--no need to remove ash & coals since they were never in the chamber. If the cooking chamber cools down below the baker's needs, the firebox vent can simply be opened again to bring the temp back up for the next batch of dough. The vent into the chamber was often covered with a pan of water to increase the humidity and close off the connection just prior to a bake. Lots of different designs out there with lots of variations on the fire box to cooking chamber heat transfer. A true white oven never has any gases from the fire directly enter the baking chamber...but again much more difficult to build...and not the only way to go.

    As you can see the white oven is quite a bit more complicated to build, however for a bakery there are some obvious advantages. There are several threads in the forum that discuss the white vs black oven and if you do a Google search on "Wood Fired White Ovens" you'll get lots of hits from bakeries that use a white oven. (as well as other information, pics, etc.).

    An excellent book that covers a lot of building options and designs is The Bread Builders: Hearth Loaves and Masonry Ovens by Daniel Wing and Alan Scott ...highly recommended!

    p.s. Roasted vegetables are terrific in a WFO. Chunked up, with little olive oil, salt & pepper...good enough that you'll forget about having the bread...and highly recommended for a diet

    Leave a comment:


  • matthanna
    replied
    I'm not allowed to eat breads, she's got me a diet of all things. What a shame - I'm totally ripped off in this project but still, happy wife happy life!

    What do you mean by black vs. white oven?

    Leave a comment:


  • SableSprings
    replied
    Matt - Relax & enjoy the adventure of the oven build...lots of help here, and lots of people who started out just as intimidated by the project (if not more so).

    A couple of comments based on my limited bread experience...

    With that projected volume of bread you will want as much insulation as possible for a smaller oven mass. That is definitely a weakness with my oven compared to those with 3"-4" ceramic fiber board under a full brick hearth...those ovens retain their heat for a long, long time when coupled with a similar thickness of ceramic batting over the oven mass.

    That said, my oven cools down and allows me to bake several batches of baguettes at pretty high temps and after an hour or two I can reduce baking temps (open door) to levels more appropriate to wheat breads, then even cooler to bake Challah & other more delicate types of laminated doughs.

    For larger batches of bread through a longer period of time and relatively constant temperature, in the future you may find yourself building a white oven (vs the black oven you are now starting).

    Again, that said, I recently saw a (very large) old black oven used for a bakery on the east coast (US) that uses a single firing for the oven and then bakes breads down to cookies as the oven cools throughout the day. Really an amazing feat of time and temperature management. I think your wife is going to love the process! (and you'll probably get to sample a fabulous bunch of tasty experiments).

    Leave a comment:


  • matthanna
    replied
    oh, and very, very intimidating :|

    Leave a comment:


  • matthanna
    replied
    Hi Mike,

    Thanks

    The wife's a solid baker and works in a bakery. She bakes a lot daily, but is hoping to start her own wood oven bakery/outlet here in adelaide. My guess is we'll be looking produce 40/50+ loaves per day though not all traditional loaves (she's very experimental and creative).

    I'm guessing that this oven will have loads of mistakes and will likely need redoing, so while I haven't been even finished my first build, I'm trying to learn as much as possible for a second oven. I'm guessing that once the first is finished, we'll be learning what works, and what's broken. Then either tear it down or build another oven with fixes to problems. If the first doesnt need replacing, we'll be improving only with the second.

    I have very little knowledge and skill in this area, so all this is quite hard and very timely.

    Regards, Matt

    Leave a comment:


  • SableSprings
    replied
    Belated welcome to the forum Matt. Out of curiosity, in your first post you mentioned that you and your wife were looking at baking mainly bread...what kind of volume (number/loaf size) are you thinking about with this oven?

    I bake mostly bread in my oven (39") but only once per week . I tend to make from 15-20 loaves every Friday and give them to my neighbors. My oven only has 3.5"-4" of perlcrete (1:5 mix perlite and cement) for its insulating slab, but holds heat plenty well for quite a few loaves of bread. The oven is covered with about 4" of 1:10 mix perlcrete. Our "record" is 30 loaves one afternoon-one firing, but the real limitation has been prep room/proofer space for us. I generally like to do a baguette style loaf (sized at 400 g) for the neighborhood and pop them in the oven (loaves - not the neighbors ) starting at 575F for about 15 minutes.

    Anyway, just curious about your bread making projected quantities. Again, welcome to the forum and good luck with the Adelaide contact via David above.

    Leave a comment:


  • matthanna
    replied
    Originally posted by RandyJ View Post
    If you are worried about thermal mass you could set the floor bricks on edge so you will have 4.5"on the floor. You could also render a layer of home brew mortar on the outside of the dome about 1-1.5 "thick. That should give you plenty of bread output. Also do 4" or more of ceramic board insulation under the oven, and don't bother with the vermicreete it is not as good a insulator and is a lot more work. Also do at least 3"ceramic blanket over the top of the dome. Then if you do a enclosure then fill the void with vermiculite as losses fill and you should have tons of thermal mass. It will take more wood and time to heat up, but that is the price you pay for very extended baking. Or if you want to cut it back a little then do the standard oven and a 1\2" cladding and the same insulation and have very good heat retention for baking.

    Randy
    Randy,

    This home brew mortar, is there are particular thread I can find the recipe? I've been searching, but no successfully.

    Thank you,
    Matt

    Leave a comment:


  • matthanna
    replied
    Thank you. I will

    Leave a comment:


  • david s
    replied
    Originally posted by matthanna View Post
    Thanks David.

    This is kind of off topic, but does anyone know of experienced oven builders in Adelaide? I wouldn't mind having someone come out to give me advice on a different issue I'm facing.
    Try giving Nissanneil a PM. He's always been keen to help Adelaide folk

    Leave a comment:


  • matthanna
    replied
    Thanks Randy.. this forum has been pretty awesome so far

    Leave a comment:


  • RandyJ
    replied
    I think you are on the right track trying to find some more oven owners near you. They will have insight on where to get stuff and what to use. I did not realize you were down under. I gave advice thinking you were in the USA . There are probably other options that might be a better value and more available. I don't know how much of the supply you have so far, but I spent roughly $6000 us to build my oven. I know fire bricks cost more in your area but it sounds like you have most of that stuff already. Good luck. I know you will find some good help on here.

    Randy

    Leave a comment:


  • matthanna
    replied
    Thanks David.

    This is kind of off topic, but does anyone know of experienced oven builders in Adelaide? I wouldn't mind having someone come out to give me advice on a different issue I'm facing.

    Leave a comment:


  • david s
    replied
    Originally posted by UtahBeehiver View Post
    Vcrete or perlcrete are economical options. Either of these options are about 0.5 as effective thermally wise than cf board, IE 6" v or pretend equals 3" cf. DavidS has a table showing the K of vcrete by ratio of cement to vermeculite. If you are on a budget and your build can accommodate the extra height and OD then these type of insulation are an option.
    This info suggests a lean (10;1) vermicrete has a similar thermal conductivity as ceramic blanket and calcium silicate board at 200 C The addition of cement to hold it together quickly reduces its insulating capacity. I also suspect the blanket performs better as the temperature climbs above 200 C Also any moisture present in any insulation layer drastically reduces its insulating capacity. Whilst a 10:1 mix is workable over the dome and is strong enough to act as a suitable substrate to render over, it is too weak and crumbly for underfloor insulation. A 5:1 mix is required there and as Russell has stated is around 1/2 as good as the cal sil board. So to get the equivalent insulation with 5:1 vermicrete as cal sol board you need to make it twice as thick. i.e. 4" of 5:1 vermicrete.
    http://www.dupreminerals.com/downloa...de-screeds.pdf
    http://www.morganthermalceramics.com...ty_sept_14.pdf
    Calcium silicate insulation brochure.pdf

    Leave a comment:

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