Malting is the process of allowing grain to begin germination and sprout, so that it will generate enzymes (amylase) to convert its store of non-fermentable starch into fermentable sugars. If there are no enzymes present, yeast will not be able to use the starch - it must first be converted into sugars. Not all the grains in each recipe require malting. As long as some (at least 20%) have been malted, there should be sufficient enzymes (amylase) present to convert the starch in the other grains. Note: this is why amylase can be added to help speed/complete malt and grain beers & worts, but it won't do a thing for thin, sugar based worts (no starch to convert).