On grinding your own burgers
I tried grinding some sirloin last night to make some burgers for dinner. Doing it in the food processor worked fine. The burgers were not as flavorful as we hoped they would be. We suspect the reason is that there wasn't enough fat in the grind. Short of trimming all the fat and weighing the fat and the meat, how do I determine that I have, say, 20% fat?
Without a scale you will be making a guess. There are a few sites with general guidelines, but I have doubts about their accuracy. Most of these guides suggest that choice sirloin is going to be 90% lean. All the ag uniiversities have guidelines :http://meat.tamu.edu/grbeef.html
Butcher shops (and even friendly grocery meat counters) are hard to beat for getting the tasty "trimmings" that make all the difference. While you won't often get the stuff for free, the price ought to be under 90 cents a pound, and if you're a good customer they'll give you a more than fair 'weigh'...
If you can't see flecks of nice white fat the stuff is too lean!
FWIW, I've never done it but have tossed around the idea of adding ground bacon to home ground burgers if they're too lean.
Try using a combination of cuts like sirloin and chuck. Sirloin for the beefy flavor and chuck for the fat. I use chuck as a stand alone cut for burgers since it has around 25-30% fat as is. You can toss some fat if you want to make it leaner. I sometimes use brisket as well since it also has great flavor and the right % of fat. I have not used a food processor for mincing meat. I have an attachment to my KA mixer and recently upgraded to a larger more powerful grinder.