Malted Barley Extract - We wouldn't dream of making bagels or Kaiser rolls without barley malt extract, and neither should you! Barley malt extract, improves the taste and texture of the breads it is used in. It goes by a number of names, barley malt extract and malt extract among them.
If a malt extract doesn't specify what grain it is made from, chances are pretty good it was made from barley. Barley is a grain used mostly in brewing beer and making Scotch Whisky. Barley malt extract adds a nice taste to breads where it is used.
For our recipes, use as light a malt as you can find, either liquid or dry, diastatic or non-diastatic and you won't have to worry about changing the recipe.
Any combination of these characteristics will work just fine. The important things to avoid are hopped malt extract which is really only useful for making beer, darker malt extracts which could overwhelm our recipes, and the malted milk powder sold in many grocery stores as a milk flavor enhancer which has too little malt in it and too much sugar. The best places to purchase barley malt extract are health food stores and brewing supply houses.
Because of differences in brands, I am not recommending a specific malt, such as light or amber. If you are confused, the staff at a brewing supply house can give you good advice. Just tell them you want a light un-hopped malt extract, and it doesn't matter if it's diastatic or non-diastatic. Tell them you're using it to make bread, not beer. They'll take it from there, though they may be surprised at this use for malt extract. We used to give our vendor a loaf of a bread or some rolls that contained malt and then they understood.
It is worth mentioning that dry ma;t extract is very hygroscopic - it will readilly absorb moisture out of the air, which will turn the lovely powder into a brick. When I was in college I was an avid home brewer and a brewing supply store offered me a great deal on 50 lbs of malt extract. Luckily I measured the malt into the amounts I used to make a batch of beer because each bag turned into its own little brick. I found I could drop them in boiling water and they would eventually dissolve. Now I keep my malt extract in air tight baggies and the baggies in a sealed food service bucket which is in a freezer. You may be surprised at how readily malt extract coats measuring spoons! Dealing with malt extract is a lot like dealing with a dog who's an escape artist - you just can't be too careful!