Dry Brining is about salting for flavor and moisture retention ahead of cooking instead of wet brining and the sort of diluted flavor some perceive from that technique.
This technique is best used on cuts of meat that have not been presalted, either with a salt solution, or koshering. You need to be in complete control of the amount of salt. You'll need to seek out minimally processed meat, poultry especially, for this technique. Generally speaking, poultry and lamb work best with this technique.
First, some definitions of terms, paraphrased or copied from Wikipedia and other sources.
Solvent: the liquid the solute is dissolved in. Water for the most part in brining.
Solute: The dissolved substance in the solution. For the most part, salt in the brining process.
Semipermeable membrane: biological membranes (cell walls of meat tissue) are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions (SALT!), proteins, and polysaccharides, while being permeable to non-polar and/or hydrophobic molecules like lipids
Osmosis: Osmosis is the spontaneous net movement of solvent molecules through a semipermeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
Let me summarize then. In a brine or dry brine, salt draws water out of the cells which increases the concentration of salt inside the cell. Simultaneously, the added water to the solution dilutes its strength pushing both the solution and the cell towards equilibrium.
So when Rick Rogers blogging at epicurious says,
He got it wrong.
When bbq.about.com says,
He got it wrong.
When Fine Cooking says the same thing, they got it wrong.
The recipes work, yes, but their explanation doesn't.
Yes even, Wikipedia sources McGee's On Food and Cooking and offers this explanation:
Rather, we know osmosis dehydrates cells, (see) secondly, cell membranes reject salt ions in osmosis. If osmosis worked as described, our uptake of water in the ocean or the bath would make us all sick and kill many of us. Of couse, the cell needs some salt to work. How does it transport salt ions? Transmembrane protiens, and that link also disccusses the rejection of salt in osmosis in the first answer.
I respect McGee and really find his book useful. But on this topic, his explanation is incorrect. I hope he corrects it in the next edition.
The last part of the wikipedia explanation is correct. The increased salt concentration in the cell (because of the lost water) partially denatures the protein of the meat. The denatured protien forms a web that helps retain the moisture during cooking that is already present in the flesh. You lose less moisture during cooking, though you lost some in the brining or curing.
So, on to dry brining, which is most often seen as a treatment for poultry. There are a couple of routes used in dry brining, but it largely forms two categories: koshering and pre salting.
Koshering poultry is a ritual process that involves a salting step to draw out any remaining blood. For the purposes of this discussion the rabbinic oversight and other steps are not pertinent and when I say koshering, I am referring to just the salting process. Chabad.org has a good article on koshering meat if you want alll of the details.
When Cook's Illustrated was doing their brining research, they observed that a koshered chicken was quite close in flavor and juiciness to a brined bird and often recommended using kosher poultry if you didn't want to brine the bird yourself. This led me to look in to the koshering process myself because kosher poultry is not easy to find my area.
The bird is rinsed, then thoroughly salted. It stands salted for 1 hour, then is rinsed three times. For just flavor purposes, the important things are this. The bird should be damp so that the kosher salt will adhere to the bird. Salt the bird inside and out, taking care to salt all folds and crevices. Let it stand for an hour on a rack or board so it can drain any liquid. When the hour is up, rinse it thoroughly inside and out.
The hour of salting time is convenient as a home cook. I can use that time as the time for the meat to come up to room temperature before cooking it. On the down side, you've rinsed the bird so the skin will be a little damp for getting that optimal crackly texture. You could dry it in the fridge for another day if that is your preference.
I often include herbs and spices with the kosher salt to help preflavor the bird. After rinsing, I'll usually reseason with more herbs and spices, but no salt. It's salty enough at this point.
Koshering is a very high salt process, a tablespoon or more a pound of meat. In the more common applications of dry brining linked above for overnight, you'll use less salt, more on the order of a teaspoon per pound. And you'll still rinse away excess salt. It's similar to brining in that strong brines are used for a short period of time, where weaker brines are used for longer periods.
In pre-salting, the amount of salt used is much less, and the time is much longer. more on the order of 1/2 teaspoon per pound and there is no rinsing.
Molly Stevens gives some good basics on pre-salting a turkey:
I've not developed nor have I seen rules for amounts or timing in this technique. Personally, I use it mostly on whole birds where the risk of overcooking the breast is high while getting the dark meat to cook to completion. The extra moisture held in the meat supplies a buffer to avoid dry breast meat. When cooking a pork or beef roast, or even cutlets and chops from pork or chicken, I can control their doneness individually as needed and so this technique offers less appeal to me in those situations.
There are those who advocate pre-salting just about every cut of meat. Food and Wine has an article that compares pre-salting on a variety of meat and found the best results in poultry and lamb. And that it was not well suited to tender pork.
Dry brining is a simple method to achieve much of the results of brining, but with less mess and hassle.