I'm not a food scientist but a fast pass on Google turns up very little good to say about phosphates. Of course, there are a lot of food police out there who think we should eat only distilled water and bean sprouts, so I was really trying to find out what phosphates DID for the food, not the politics. My research said they are an acidifier and emulsifier and that phosphate salts increase flavor intensity. There are natural, organic phosphates occuring in most high protein foods but extra (assumed not "natural") phosphates are a common additive.
Translating the above I'm going to assume that adding phosphates helps with tenderness and flavor. Duh? I'll also assume that the occasional consumption of phosphates is probably not the end of the world unless you are a food nazi. So . . . back to your question:
I didn't see anything about intensity of phosphates by kind or brand and I didn't see anything about recommended levels by meat or type of food preparation. If you want to put in the effort you might find something on that if you really want to get into great depth. Let us know if it is useful.
Suggestions:
1. I share your opinion that sometimes commercial injections produce a flavor I don't like. I have a hip-pocket opinion that over-injection of this type produces the "pot roast" effect I sometimes encounter in judging. I could be wrong -- maybe the cook boiled his brisket with carrots and taters to do that
. When I use Butchers For Beef I mix it 1/2 strength -- meaning twice as much water or half as much mix to get to the amount I need. I've never had a brisket I've cooked this way taste "potroasty" or any flavor I didn't think was appropriate. Whether you use the injection mix or pure phosphates, try it half-strength and see if you like the results.
2. You can make your own injection and I know lots of cooks who do. Broth, salt, garlic and onion show up on their recipes along with MSG sometimes (a tenderizer and flavor enhancer) and other stuff. You might try some non-commercial approaches to the injection construction.
I use injection primarily to assure moisture, not add flavor. A little touch of flavor is okay, but I want the flavor of my brisket to be an interesting balance of the beefiness of the meat, the contribution of my rub to the bark, and the compliment of my sauce. I expect the injection to help produce a moist texture (brisket is notorious for coming out dry-tasting, even when it is tender). I've never tried it because I like the results I get with half-strength Butchers, but water might produce the same or a similar result.
Sorry for the long answer, but I really like your question and it is worth your time to get to a brisket you like and are proud to serve. Let us know the results of your quest
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