Hi Toolhawk,
By their very nature, beef middles under the right conditions, can make a soiled baby diaper smell like a handful of lilacs! As you probably know, the middles are behind the rounds (also called the "runners") and they are part of the naturally straight, large intestine. Bovine middles are tougher than porcine middles and during preparation they should be covered with cold water and saturated for a longer period. Flush them as you would any other casing to wash out any residual packing salt and to cleanse the interior one last time before they become part of your project. Actually today`s processors perform a remarkable task in cleaning them although once in a while you may discover one that needs just a "little more attention". Another peculiarity you will probably discover is that during the dry-curing process, they often become more "slimy" than pork middles. If this happens during the "drying" period, simply wipe them with a clean cloth.
I recently discovered some beef middles that I had washed (upon arrival) and placed in a saturated salt solution inside a plastic bucket to have "on hand" in my shop. Somehow they were placed in the freezer - more than ten years ago!

As I was defrosting the freezer to clean it, I discovered them and was curious to know how they had held up. After thawing them out and removing the lid, a ruthless, wafting, whiff of alarming aroma hit me like one of my wife`s well-positioned black skillets! After two neighbors picked me up off the floor, one of them was actually able to revive me. Then I noticed the hole in the ceiling where the blue stench cloud had eaten an exit from my kitchen. Immediately, I began receiving phone calls from irritated neighbors with awful attitudes complaining about something they called, "odiferous and noxious gaseous warfare". On the other hand, I washed and flushed the casings after one of my friends stapled my nostrils together. Wheeee Eweeeuueee! What a fragrant fecal fetor factor! What an emanating essence of putrid pungency! What a bouquet of bull!
Having been "refreshed", the casing appeared to be just fine, so I stuffed a couple with a semi-dry-cured type sausage. Having been smoked and cooked, I found the casings to be a little on the tough side, but otherwise satisfactory.
Best Wishes,
Chuckwagon