what ingredient can i use to keep my wheat bread moist and soft when it is finish baking.
Here are three easily found ingredients in any supermarket and often already in many homes. The first ingredient is some butter, unsalted is preferable. I use between 15 and 30g of unsalted butter in loaves where the total flour weight is at least 400g. The next suggestion is to use either potato flour or instant mashed potato flakes. They help retain moisture in the loaf. Finally, substitute some milk for the water in your recipes.
Strictly from my own experience and not based on a scientifically controlled study, I suggest that you soak your whole wheat flours before you mix them into the main dough. Figure out your target hydration for the loaf and soak the whole wheat flour with a corresponding amount of water or liquid. In other words, if the bread's hydration is expected to be 67% and you're using 100g of WW flour, soak the flour with 67g of water for at least an hour before mixing it into the dough. That works well for me. Should you try that in your bread, please let me know of your results.
PostalGrunt is right. The reason why WW loaves become dry or crumbly after baking is that the bran bits are finally able to soak up the moisture from the loaf after it sits.That is when the crumbling/dryness begins. In order to preserve the moisture and keep the loaf soft after baking, you need to soak the flour (and all those lovely bran bits) before the bake. This is as simple as mixing the liquid into the flour and letting it sit for 30-60 minutes or even overnight. Because the flour and bran is soaking up the moisture, you may need to add a little more liquid for WW than you do for white bread. (All bread improves with a well-hydrated flour,though.) The best description is that the dough is actually sticky-when you touch the dough, some dough actually comes away and sticks to the finger, as opposed to tacky, when the finger seems to want to stick a little to the dough but comes away clean(like a post-it note). So you want the dough to be slightly sticky when you are done mixing,rest 30-60 minutes and by that time be tacky,then knead. I actually make many of my WW doughs up late in the evening and put it in an oiled plastic container in the refrig overnight and shape/proof/bake the next morning.
Enriching the dough with milk,fat (oil or butter),potatoes or eggs help keep the crumb soft but the loaf will still crumble if you haven't given the flour time to absorb the moisture into its bran bits.
There are many ways to get the loaf to stay soft but technique is probably as important as ingredients.
After removing the loaf from the oven, and or bread pan, cover the loaf with a kitchen towel for 15 ~ 20 mins.
If you don't mind a sweetner, I suggest honey. It will keep your bread moist and resist spoliage.
is the most effective trick to retain some moisture and the crumb soft for several days, in my opinion. There are a lot of threads regarding water roux here on TFL.