<<Disclaimer: Verify this information before applying it to your situation.>>

With regard to my prior post on the effect of using flaxseed as an egg 
substitute to increase GF bread volume and reduce cave in tendency 
(illustrated in "Tips & Recipes" at http://www.gfbakingpans.com ), I 
only received a few replies.  Two mentioned the flaxseed egg 
substitution method is described in some recipe books.  However, I got 
my information by simply Googling "flaxseed egg substitute".  One 
reply reported:

"For several years I have been adding flax seed ground in a coffee 
grinder to my breads and baking. I started using it to add nutrition and 
then noticed it made my breads more substantial and tastier."

I did some further research.  By Googling "flaxseed bread volume", I 
found that flaxseed meal making up about 25% of wheat bread results 
in decreases wheat bread volume and increases rising time.  But this is 
expected for wheat bread.  The addition of flaxseed meal reduces the 
amount of gluten in the wheat bread.  The problem is corrected by 
simply adding gluten to the flaxseed/wheat flour recipe.

However, for gluten-free bread, the story is different.  If  you 
Google "flaxseed gum", you will find a wealth of knowledge.  Flaxseed 
gum, derived from flaxseed mucilage, has properties similar to xanthan 
gum and guar gum.  Flaxseed gum has been shown to improve muffin 
height and volume and is also used in salad dressings.  Depending on 
the reference cited, flaxseed gum can be extracted from flaxseed and 
makes up about 5% to 13% of the flaxseed.  The amount of mucilage 
in flaxseed varies widely depending the source of the flaxseed crop, 
see:

Crop Sci 46:365-371 (2006)
Variation of Mucilage in Flax Seed and Its Relationship with Other Seed 
Characters 
Axel Diederichsen, J. Philip Raney and Scott D. Duguid 
http://crop.scijournals.org/cgi/content/full/46/1/365 .

Hence, different baking properties may be expected from using various 
sources and varieties of flaxseed.  The first step in extracting flaxseed 
gum from flaxseed involves placing the flaxseed in water near the 
boiling point, 90° to 100°C.  Therefore, the egg substitution method, 
which involves steeping 1 Tbsp ground flaxseed in 1/4 to 1/3 cup 
boiling water per egg for 10 minutes, results in flaxseed gum 
separation making the gum more readily available during baking.  
Steeping flaxseed in boiling water may be a necessary step in using 
flaxseed to increase gluten-free bread volume and height.  Just adding 
dry flaxseed meal to a gluten-free bread recipe may not be as effective.

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