Difference in long or short oven steam time?

Hi, I've found that the longer I leave my loaf in steam, the thinner and softer my crust.

Mat

I believe that it depends on the type of dough that is to baked. Whole wheat, and whole rye breads do not require more than 10-15 minutes steam, as the crust will thicken and be leathery quickly. White doughs can be steamed for upto 20 minutes, depending on dough size.

-Khalid

a little steam will slow the crusting of the bread.  this is supposed to help oven rise as things can expand more before the crust sets. you also get that nice blistering with steam during the first 10-15 minutes of the bake.  why do some steam longer or shorter than others - I can't say for sure, but it can be just a bakers preference.  some like a crisper crust, some don't.  some breads are better with a crisper crust, some aren't (compare say bagels to white sandwich bread).  stream as much, or as little,  as you like to get loaves the way you like them.  since you're doing the baking, you're the boss and can have it any way you like! 

size of the loaf or bread.  Bagels 7-8 minutes and 16 min total.  900-1000 g loaves 15 minutes of steam and 30 minutes total baking time  1,400 g loaves 20 - 25 minutes steam and 40-50 minutes total baking,  I shoot for half steam and not to get the best crust.  Why blisters form sometimes and other times not is a good question too.

Pumpernickel's are under steam the whole time and some high % rye breads will have longer steam too.

Questions about steaming ovens for bread baking are asked pretty often on TFL. Most of them pertain to steaming methods for home ovens. Sometimes, other questions are asked the answers to which pertain to steaming, for example, "Why is my bread's crust so dull?" Questions regarding how long to steam usually get answered in terms of anecdotal experience, and, given the variability among home ovens, maybe that is the best we can do. Yet, it seems to me, some attention to the actual functions of oven steaming may provide each of us with some basis on which to objectively determine how much is enough for our ovens.  

The effects of oven steaming on bread

The most important effect of steaming the oven is to delay crust formation. When bread is loaded into a humid oven, and the moisture is retained for the first part of the bake, a thin film of moisture forms on the surface of the loaves. This delays the surface drying out and becoming rigid. This allows maximal expansion of the loaves during oven spring, because they are not constrained by a stiff outer surface. Thus, a greater loaf volume is achieved. When the loaf surface is expanding as the crust starts to form, the result is a thinner, crispy crust. Eventually, the crust does form, even in a moist environment. After this starts, more moisture is not helpful and, in fact, may lead to a thicker, tougher crust.

This surface moisture has a couple more beneficial effects. At the start of the bake, as the dough begins to heat up, there is an increase in enzymatic activity. The surface moisture, by delaying drying out and through evaporative cooling, prolongs the period of increased enzymatic activity. This frees more sugars from the starch in the dough, and these increase the Maillard reaction and, thus, contribute to a pleasing crust coloration and improved aroma and flavor. When exposed to water as it heats up, the starch granules on the surface of the loaf burst, and the starch gelatinizes. This  gelatinized starch forms a film which reflects light. We see this as a shiny crust.

All of these beneficial effects result from a moist oven at the start of the bake. Ideally, the oven is humidified before loading the bread and humidity is maintained until crust starts to form, usually indicated by the start of visible browning. Generally this begins 12-15 minutes into the bake. Steaming for longer than this is of no benefit, and, under some circumstances, can be harmful. Most home ovens don't retain steam very well, so over-steaming is usually not a concern. However, if the steam is trapped, for example by baking in a covered container, one can easily overdo it. The usual result is a loaf that is overly shiny. However, if the loaf is somewhat over-proofed, while a little steam can enhance oven spring as described above, too much steam can delay formation of a crust that is needed to support the expanded dough and result in loaf deflation and decreased loaf volume.  Similarly, the right amount of steaming is necessary for good bloom and ear formation. Excessive steam can promote collapse of the elevating flap of dough with decreased bloom and a flat surface without good ear formation.

Factors that influence how much oven steaming is enough

1. In general, under-proofed bread may benefit from longer steam exposure. Over-proofed breads need earlier crust formation to support their fragile structure, so a shorter steaming period is needed.

2. Breads (or rolls) that have been egg washed are generally not steamed at all.

3. Sourdough breads without added bakers' yeast need longer steaming. Sourdough breads, compared to breads leavened with commercial yeast, have slower, more prolonged oven spring. Therefore, they benefit more from having the oven humidified before the loaves are loaded and from more prolonged steaming to keep the crust flexible longer to achieve optimal loaf volume. 

This information was abstracted from Bread, by Jeffrey Hamelman and from Advanced Bread and Pastry, by Michel Suas. Any errors in the above are mine.

I hope this helps.

Happy baking!

David