Let me be honest, when using green grass clippings I have not been able to avoid some smell. A bag of grass clippings left sitting by the curb for just a couple of days will already have started heating up quite a bit. When that bag under those conditions is opened (especially if it was wet when cut) that grass is going to smell(stink). Strangely, the variety of grass has a lot to do with the smell. Some grasses just smell a lot worse to me than others in that state, some stink to high heaven, others seem to maintain that strong freshly cut grass smell for a much longer time. If I have a really smelly batch of grass clippings, the first thing I do is spread them out then cover them completely with shredded leaves or aged compost just to smoother the smell. Later I can work with getting the mixture correct after the smell has abated. Then in the perfect scenario, I have enough shredded leaves to mix in with the grass clippings and start the actual composting process. Now, if the grass is freshly cut and not allowed to sour, the stinky smelly can be avoided and only the fresh cut grass smell will be noticed when building the pile. If done properly with a mix in the right proportions the sour grass smell won't be a problem. However as with any pile if the moisture and mixture is not correct you can still end up with a smelly pile, and I often feel my compost if lacking anything is lacking in nitrogen for that reason.
But, I pick up lots of grass clippings and sometimes the grass was cut when wet, bagged and left sitting in the hot sun for days before I find it. So I cannot say my compost processing creates no stinky smells. I said earlier than I use no manures when composting, but for several days after I return form a successful hunt for composting materials on a hot summer day you would swear that I had a stable available for a nitrogen supply.
Now making leaf mold, which to me is also composting, though many may not think of it as being composting, is a way to make compost and almost have no composting smells. To me the mixture of leaves heating up and decomposing gives off many different smells, and often I find them very pleasing smells, the different leaves give off different odors. Of course normally, I seldom have piles made up of nothing but leaves, here in S.E. Alabama there is normally at least a small amount of grass mixed in up until late winter, and often then a heavy mixture of dried dead grass clippings are in the leaf piles. So here, winter time is to me, the best time to start to create as much compost as possible, the awful stinky sour grass smells can be totally avoided, yet our weather allows the decomposition process to still continue. Of course, not nearly as fast as during the heat of summer. The summer compost piles I create can be finished in a couple of months, the winter piles take over twice as long, and often won't get used for over six months to a year.
