July 5, 2017 - 9:22pm
How much steam is enough steam?
I picked up a small humidity/temp gadget off of Amazon. I left it in my gas oven, and found that sitting with the pilot light, it's at about 10% humidity and 115 F.
I wangled together a pot and some clamps and a copper tube I ran through the exhaust of my oven to create a steam injector. (image attached is of an earlier attempt, but materially the same. The gadget is up at the top.)
I ran it for a while tonight in part to make sure the seal wasn't good enough to build too much pressure, and to see what it did for the oven. The gadget read 45% humidity after about 7 minutes of steaming... but I don't know what it would be normally cause I've never measured it. Does anyone happen to know how humid steam injection usually makes an oven?
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I commend your attempts at injecting steam.
While I cannot say what humidity level is correct I think I can add some thoughts. As you know, the warmer the surrounding air the more humidity required to saturate it. What might be adequate at 300 F may not make a dent at 500 F.
The venting properties of your oven will have a big effect on steam retention. My deck oven vents its combustion gases straight through the baking chamber, then straight out the flue. Many commercial ovens are a box in a box, in other words the baking chamber is isolated from the firing chamber. From my perspective the best steaming ovens are sealed with a way to inject steam and a way to vent it on demand. With my oven I have to constantly inject steam at 5 - 7 psi. to try to keep the humidity levels satisfactory. I have seen professionals close the baking chamber vent, press the steam button for 3 - 5 seconds, walk away for a few minutes then return to open the vent.
The reason I bring this up is that you may be fighting an uphill battle with the limited amount of steam generated by a pressure cooker - or maybe not. My baking chamber is about 3 cubic feet in size and I have to deliver steam at a rate of 5 - 10 pounds per hour to create the oven spring I need. A pint of water is a pound so I would have to evaporate 5 - 10 pints of water per hour. I can do this with a single 4000 watt heating element running @ 240 VAC. If your baking chamber seals well you can create the same saturation level with much less steam and much less power.
Now I cannot speak to the math of heat exchange and water transfer but, if your dough hydration is 70% and your oven air hydration is 50%, my guess is that water is evaporating from the bread dough into the air. The larger the differential the faster the transfer. The higher the heat the faster the transfer and the more water needed to create a balance.
As I ramble on I think my suggestion would be to determine how well your oven RETAINS humidity then take the appropriate action to either, create more steam or create better retention. Messing with retention in an oven fired by gas may not be advisable since you may also limit combustible air. I know this because if I push the steam level too high I will remove enough air so that the flame is extinguished on my burner.
Best of luck and please keep us posted.
Jim
Your 3 cubic feet = 5-10 pounds water ratio - how did you calculate that?
I suppose I'm just going to have to make lots more freeform loaves over the next week or so, and see if the steam changes the crust. I don't like experimenting that way because there's so many other variables, but maybe it'll be clear in the crust quality...
Reimers, the steam generator manufacturer, suggested I plan for 3 - 5 psi. for the deck oven. I also saw a similar notation in the manual for the Blodgett deck oven so they seem to be in agreement. I have learned that psi. is only one factor in the delivery of steam and that we can generate 5 psi. with a teaspoon of water or a gallon. Saturation is more about how much throughput the generator can manage. Psi is about getting good dispersion without eventually spraying water droplets on the surface of your bread.
My current steam generator max's out at about 5 lbs. of water per hour and it really isn't enough. I am upgrading the generator now to deliver about 13 lbs/hr and still have the option of going as high as 27 lbs/hr. I know that 5 lbs/hr isn't sufficient through experimentation and not through a formula-driven solution.
If I throttle back the steam so that I can continue steaming the bread for 10 minutes, my loaves have good oven spring, a moderate crust and a small amount of grigne. If I blow the total contents of the generator in more like 3 minutes I might have moderate oven spring, a blowout or two, moderate crust and impressive grigne. Baguettes are more akin to the shorter dump time but larger rustic and pan loaves require longer steam times - sometimes up to 20 minutes.
Recovery time is also an issue. With my current set-up it might take 20 - 25 minutes for the generator to recover after dumping all the steam. This really slows down throughput on a busy day.
While you might not want to experiment with several batches of bread it may be your only solution. Since you probably cannot quantify the air mass throughput of you oven now, my assumption is that you will have to continue to test batch after batch to dial-in your steam quantities.
fupjack , does the humidity/temp gadget you got from Amazon works while the oven is set to 550 F?
Since the steam was coming from the stovetop, I was running that without turning on the oven - cause if I set the oven to max, the gadget would melt. There are probably measuring instruments that can withstand the heat, but this is a pretty cheap device.
I was hoping you did. I am working on a design that will boil 2 to 3 cups of room temperture water in about 4 minutes, and evaporate in less than 10 minutes in an electric home oven set at 500 F... I have been meausring the water temperature vs the oven temperature, it will be nice to measure the humidity also.