Question about brining
I've been reading all about brining and how it makes poultry (turkey in particular) more moist, which sounds great. Then I started thinking about what I know of osmosis from my high school science classes, and realized that brining should make water move out of the bird, not in--so I'm very confused. If it were soaked in pure water, I could see the water moving in, but adding salt and sugar should make the water move out to equalize the concentration. Can anyone explain?
Please correct me if I'm wrong! My impression is that the above posts may be partially correct, but they are missing an important piece.
If placed in pure water: Pure water has no salt or sugar in it, so you would draw out any salt or sodium that is naturally occuring in the turkey because the meat and water are trying to establish equilibrium (equal percentages of salt inside the meat (turkey) and the water surrounding it. When brining: Essentially you're creating a saturated solution outside of the bird which consists of a high amount of salt and sugar. The meat and the surrounding saturated water you have now placed the turkey in want to be in equilibrium. The turkey, by far, has less salt & sugar in it so the saturated solution moves into the meat taking with it moisture and whatever flavoring you have added. The movement of the water and salt/sugar is the restoring of equilibrium.
The turkey meat has other solutes in it which have higher osmotic pressure than the brine solution. Hence water from the meat moves into the brine. The size of the cells in the permeable membrane (the meat surface) does not allow the solutes to pass into the brine solution because the solute molecules are too large. However salt is a smaller molecule so it can pass from the brine into the meat.
The whole process consists of (1) osmosis - passage of molecules from a higher density solution to a lower density solution across a permeable membrane and (2) change in the protein structure due to denaturing by the salt.
Ok, that makes sense. There seem to be several theories out there, so who knows what's actually happening!? I just found this... Read below from Virtual Weber Bullet:
There is general agreement among food scientists and writers that the processes of diffusion and osmosis are involved in achieving equilibrium between the flavor brine solution and the meat--in other words, that these processes attempt to balance the difference between the amount of water, salt, and flavorings in the flavor brine solution and the amount of water and dissolved substances inside the meat cells. However, opinions differ as to the mechanics of this balancing act.
The most commonly offered explanation is that the flavor brine solution contains a higher concentration of water and salt than the meat, so the solution passes into the meat cells through their semi-permeable membranes, adding water and flavor to the inside of the meat cells. This explanation is offered by authorities including Cook's Illustrated magazine and Robert L. Wolke, author of What Einstein Told His Cook: Kitchen Science Explained.
Other experts state the opposite situation, but with the same end result: That meat cells contain a higher concentration of water and dissolved solids than the flavor brine solution, so the solution passes into the meat cells through their semi-permeable membranes, again adding water and flavor to the inside of the meat cells. Shirley O. Corriher, author of CookWise, provides this explanation in her book.
Yet another explanation is that the flavor brine solution does not actually penetrate the meat cells at all. Instead, it just flows into the spaces between cells, where it draws out some moisture through the semi-permeable membrane of meat cells, increasing the concentration of naturally occurring sodium inside the cells. Some of the flavor brine solution remains between meat cells where it flavors the meat. The California BBQ Association Web site provides this explanation in an article written by Joe O'Connell.
Regardless of the explanation, all sources seem to agree that a higher concentration of salt inside meat cells causes protein strands to denature. The tightly wound proteins unwind and get tangled together, and when heated, the proteins form a matrix that traps water molecules and holds onto them tightly during cooking. In the case of the first two explanations, the denatured proteins hold on to some of the water, salt, and flavorings that flowed into the meat cells; in the case of the third explanation, the denatured proteins are holding on to free water that was already inside the meat cells and would have been lost had the meat not been brined.
Which of these explanations is correct? I'm not sure, but in the end, it doesn't really matter. The bottom line is that flavor brining results in meat that is more moist and flavorful than unbrined meat, regardless of which explanation you choose to believe.
The text from Virtual Weber Bullet is misleading, because the two first competing explanations (from Cook and Corriher) are impossible are they are described. The key thing to understand is that the movement of the salt does not carry the moisture with it (sorry Haagen Dazs): salt and water each diffuse independently (and often in opposite directions).
Cheryl_h's summary is a very good one: brine initially draws water OUT of the meat, but reduces the "squeezing" of water out of the meat during cooking by denaturing meat proteins.
Water and solutes move by diffusion -- osmosis is just the special name we give to diffusion of water. Any dissolved substance (including water) diffuses away from where IT is at higher concentration to where IT is at lower concentration. In other words, it moves down its concentration gradient. Brine has a higher salt concentration than pure water (say, 10% salt ions vs. 0%). However, brine has a LOWER water concentration (90% water vs. 100%). Therefore, if a permeable membrane separated brine from pure water, more salt ions would move from the brine into the pure water than the other way around. The opposite is true of water -- water molecules would move from pure water into brine. The movements of these two substances are independent, and each moves down its own concentration gradient.
So, the meat cells cannot "contain a higher concentration of water and dissolved solids than the flavor brine": it can only have one or the other. If water concentration is higher in the cells, then solute (dissolved solids) concentration must be lower. Water always moves toward where the concentration of solutes is higher (and hence concentration of water is lower).
Now, let's apply this to our turkey soaking in brine (injected brine is a whole different story): the brine typically has a higher concentration of solutes (salt and sugar) and a lower concentration of water than the meat (otherwise, we could just plunk it in pure water). Therefore, salt will tend to diffuse from the brine into the meat and water will tend to diffuse out of the meat into the brine: the meat gets saltier and drier. If allowed to go on, diffusion will proceed until each substance reaches the state where its concentration in the meat is the same as in the brine.
So, how does brining make turkey juicier when it actually draws water out of the meat? Here, the second purpose of brining -- denaturing proteins -- comes into play. You've all probably seen the result of plopping raw and unbrined turkey or chicken meat into boiling water or stock: the meat immediately condenses and becomes rubbery. The rubbery texture is due to the immediate response of meat proteins to heat: they contract. This contraction causes the tissue to squeeze like a sponge, creating pressure that actually defeats the osmotic pressure from the outside (the fact that water is trying to diffuse out of the water or stock and into the meat) and reduces the overall moisture of the meat. Simmering for longer periods breaks down the proteins further ("denatures" them) so that the tissue begins to fall apart, the contraction force lessens, and water can diffuse in unopposed. The salt in brine denatures these proteins BEFORE heat is applied, and therefore reduces their contraction in response to heat. So, although brined meat starts out with less moisture, it actually has more at the end of cooking because it hasn't been wrung out like a sponge.
By the way, the denaturing of the proteins does not affect their nutritive value -- they're still made up of the same amino acids, just in a different 3-D shape. Your body's enzymes digest the proteins just the same.
I hope this helps somewhat
Initially water moves from the meat into the brine but salt moves into the meat. The salt dissolves part of the protein structure which collapses the cell walls. That draws water back into the meat. Also, as already said, the coagulation of the denatured proteins holds water which is retained even when the meat is cooked.
When brining a turkey 14-16lbs I leave it in for 8 hrs. From what I understand while the water infuses with the meat it leaves behind all the flavorings. I brined my first bird a few years back (see food t.v. alton brown?) and it was fantastic. It continues to be a big hit, I don't cook turkey any other way! No stuffing, just aromatics!