A Tip of the Toque to Professor Chaos for this idea. I'm going to try getting back into the swing of blogging by starting a new feature: Sous What?, a semi-regular post in which I will answer some culinary question posed by a reader. Bearing in mind that I'm still a culinary student and not a culinarian yet, let alone an actual chef, some questions will require I do some research before answering. But this weeks question, posed by the aforementioned Professor Chaos, I can answer now:
What's the difference between a marinade with a base of water vs. having a base of oil?
The main differese is that water-based marinades, and their close relatives brines, will dry food, especially red meat, out more than oil-based marinades. This is largely due to the salinity of the marinades (hence the term brine). Fat, which is what oil is, just vegetable fat, preserves moistness. It seems counter-intuitive, but that's how it works, especially with grilling, frying and sauteeing. Add some acid to cut the fat -- red wine, citrus juice, and vinegar being the top three options.
That's not to say that fatless marinades don't have their place. If you plan to use a moist heat cooking method, such as braising or stewing, dryness isn't going to be an issue.
And there are, of course, exceptions to every rule. Slow cooked food is the exception in this case. Alton Brown recommends brining turkey to make it moister. Smoked fish is brined then dried, creating a layer called a pellicle that retains moinsture in the meat. And when I barbecue brisket, I marinate it in a fatless marinade, but one that's fairly low in salt, and it's further mitigated by the way the meat is cooked -- fat cap up, so all that yummy fat melts into the meat. But for leaner cuts of meat, and cooking on a grill or stovetop, I'd go with an oil-based marinade.
My Chef Instructor has made it clear to me that brine-based marinades and brines CAN be used on thinner cust od meat, but the amount of time they're used is decreased -- any longer and drying will occur. The general rule of thumb is 1 lb. of salt per gallon of water, which results in a brine of about 20% salinity. This salinity is optimized for penetrating 1/2" of meat per side per hour. That means an inch-thich steak is being penetrated from both sides and needs on 1 hour in the marinade.