Malted Barley Flour
Malted Barley Flour is made from barley that is malted (e.g. barley that is allowed to germinate), steam-dried, hulled, then ground and sifted. It is usually made from the species of barley that has six rows of seed to it per head.
Technically, because it's malted, it has increased enzyme activity. More precisely, it contains alpha amylase, which helps to break down complex sugars and starch in the dough to simple sugars such as maltose, making them easier for yeast to feed on.
There are actually two kinds of malted barley flour, diastatic and non-diastatic.
- Diastatic: This is the kind normally meant when malted barley flour is mentioned: it's the one that has the active enzymes in it and is the one used for baking. It doesn't actually have any real flavour to speak of, so it's "flavour-neutral" in what you are using it for (though some specialty ones can have more flavour.) Nor does it impact colour much. What it does do is give a moister crumb;
- Non-diastatic: This has no active enzymes in it; it used for flavour, in a variety of applications and in baked goods, to give a glossy surface and a soft, fine crumb. This is more likely to be referred to as "Malt Powder."
The United States Department of Agriculture (USDA) allows malted barley flour as an additive to all-purpose flours, whole-wheat flours, and bakers hard wheat flours.
In baking, malted barley flour needs to be used in combination with wheat flour. For yeast risen goods, you can safely swap in up to 1/4 Malted Barley Flour; for non yeast-risen baked goods such as cookies, quick breads, up to 1/2. For recipes where there is no rising at all happening (e.g. using it as a thickener for gravies, soups, stews), you can use 100%.
It is used commercially a great deal in bread, pizza crusts, crackers, rolls, pretzels etc as a dough conditioner -- because of its lower gluten, it causes the dough to be softer, more relaxed and gives a softer crumb texture.
Malted Barley Flour contains a small amount of gluten, and a good bit of fibre.
It contains some tannins -- some people who are very prone and senstive to migraines may find that the tannins aggravate their headaches.