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Brining - the science
By JOE O'CONNELL, cbbqa Past President
Meat will dry out when covered with salt, but brining seems to make meat moister. Since a brining solution is simply water and salt (with perhaps some spices added for flavor), is there a contradiction here? Should brining not result in dried-out meat rather than moister meat? The following explains the "why" for the curious.
Cooks who are not so curious may skip the science but remember two simple rules:
Because salt dries out the surface of meat, the general rule is to salt meat after cooking, unless there is a specific reason that the meat's surface should be dried out before cooking. For example, many barbecue rubs contain salt for the purpose of drying the meat's surface to make it crusty.
Also, most poultry (chicken and turkey) should be brined before it is put in the pit for barbecue, because the low 'n slow barbecue method tends to dry out poultry, and brining helps keep it moist. Now, for the science.
Meat is muscle tissue, which in turn is made up of individual cells and connective tissue. Meat is composed primarily of two types of cells:
These cells and connective tissue are in turn made up primarily of four types of molecules, and their percentage presence in lean meat are (see McGee at 87):
The muscle cells of meat are long, thin fibers, some of which exceed twelve inches in length. The individual fiber cells are bound together by thin sheets of connective tissue, which is not itself living tissue but a protein structure which surrounds the live cells that created them. Bound fiber cells are grouped together in bundles to form individual muscles. McGee at 87-89.
Meat also includes fat tissue. Some fat is dispersed invisibly among other tissues, but most fat in meat is concentrated in adipose tissue, which is composed of specialized fat cells. McGee at 530.
Adipose tissue is the fat tissue which surrounds muscle tissue. Marbling refers to the fat tissue which is incorporated into the muscle tissue and appears as patterns of white splotches in the red matrix of muscle. McGee at 90.
Fat cells contain a high percentage of water than other meat cells, and it is the water content of fat which makes cooked meat moist.
Carbohydrates are sugars and long chains of sugar molecules, like starch. In meat, most carbohydrates are converted into glucose, which is the preferred food of muscle cells. While most cells can burn fats for energy, the brain and other nerve cells can use only glucose.
Glucose is stored in meat tissue as glycogen. Glycogen is stored in the liver and throughout muscle tissue. McGee at 527 ff.
Proteins are molecular structures composed of carbon, hydrogen, oxygen and nitrogen. There are many different types of proteins, but all proteins are built from a few basic units, called amino acids. Proteins include many different types:
Proteins are the largest component after water in meat (muscle), internal organs, bones, blood cells, skin, hair, and teeth.
Fats are specialized molecules which are used by muscle and other cells as one of the two primary sources of energy (the other source is carbohydrates). Measured by weight, fats store twice as much energy as carbohydrates.
Fats in cooked meat give the meat more flavor, a smoother texture and account for the sensation of "fullness" when eaten. McGee at 530.
Fat molecules are present in meat cells -- in the cell membranes and cytoplasm. Fat molecules are the primary component of fat cells, which are storage tanks for fat molecules held in a network of connective tissue -- fat tissue or adipose tissue -- which helps insulate the muscles and provide a source of reserve energy. McGee at 90.
Water molecules are found both inside the cells (intracellular water) and in the space surrounding the cells (intercellular water). Some water molecules are free -- either unbonded or very lightly bonded with other molecules -- while some water molecules are bonded tightly with proteins and other molecules.
Meat cells are contained by cell membranes that keep the cell contents from flowing into the intercellular spaces, and the cell membranes keep most molecules from penetrating into or exiting out of the cells. Most molecules cannot penetrate through the cell membrane from outside a cell, but there are exceptions, as will be described below in the discussion of osmosis.
There are several different kinds of cells in meat tissue, and each kind contains different amounts of water. The cells that contain the most intracellular water are the fat cells. The reason that a Prime Grade beef steak is moister than the same cut of Select Grade steak is that the Prime Grade meat contains many more fat cells, which contain many more water molecules, which means that the steak will be moister when cooked and eaten.
Inside each kind of meat cell, there are many different bundles of long proteins. Proteins are complex chains of molecules which can hold other molecules, like water. Normally, proteins are coiled up tightly with bonds that hold them in single units. Tightly coiled proteins cannot bind with very many water molecules.
However, when a protein is cooked (by heat, acid or drying -- this is very important, since drying, as by sodium, "cooks" protein), the protein bonds break down, and the protein bundles straighten out. This is called denaturing. When proteins are denatured, they can bond together with other molecules, like water and other denatured proteins. This is called coagulation.
This process is seen as a raw egg begins to cook:
This same process applies not just to eggs but to all meat.
Water within meat
As the internal temperature of meat proteins remains between 100°F and 120°F, the protein bundles shrink slowly in size, but the proteins continue to bond with water molecules, so there is minimal moisture loss.
However, as the temperature of the proteins reaches and passes 120°F, significant moisture loss begins to occur, because the proteins cannot retain the bonds with the water molecules. The water molecules flow from the meat and are lost. This is popularly called the first sweat. The first sweat results as water molecules are unbonded and freed from the space between the individual cells. Note that the first sweat is not evaporation but the freeing of water molecules from the intercellular spaces and protein bonds.
The second sweat takes place when the cells themselves begin to break down, which occurs normally when the internal temperature of the meat cells exceeds 140°F. At this temperature, the individual cells break apart and release the cells' contents, including the unbonded proteins and molecular (free) water. This loss of intracellular molecular water at a temperature above 140°F gave rise to the term second sweat.
Salt and osmosis
As described above, 120°F and 140°F are the normal temperatures at which intercellular water molecules and intracellular water molecules, respectively, are released from meat proteins and may be lost during cooking. However, these temperatures can be increased by brining or salting, through the process of osmosis.
As described above, the cell membrane of all animal cells keeps the intracellular proteins and other molecules inside the cell and keeps the intercellular molecules outside the cell. But there is an exception: water can pass through a cell membrane in certain circumstances.
There are many different kinds of salts, which are the reaction product of an acid on a metal. Here the word salt will be used to refer to ordinary table salt.
Salt (ordinary table salt, to be precise) is a molecule of sodium chloride. That is, table salt is a molecule that combines one atom of sodium (Na) and one atom of chlorine (Cl), which forms a molecule of sodium chloride (NaCl), which combines in a cubic crystalline form when dried.
Inside muscles (meat), sodium and chlorine are separate atoms: sodium is a positively charged ion, and chlorine is a negatively charged ion. With other elements like potassium and phosphorus, they regulate the concentrations of other chemicals inside and outside cells.
Sodium and chloride are the principal mineral atoms in the blood plasma, and potassium and phosphate are the principal mineral atoms in the cellular cytoplasm. McGee at 544.
Sodium and other mineral atoms act across the semipermeable cell membranes form an area of higher concentration to an area of lower concentration, in a process called osmosis. Osmosis means the diffusion of certain molecules across the semipermeable cell membranes (walls) in order to equalize the ion concentrations of either side. McGee at 544.
In living tissue, osmosis is important to maintain life itself. For example, if there is "too much" sodium in the blood -- i.e., if there is a higher concentration of sodium in the blood than in the muscle cells -- then water molecules will pass through the cell membranes and into the blood. This will increase the number of water molecules in the blood and thus reduce the sodium concentration in the blood, while at the same time it will decrease the number of water molecules inside the cells and thus increase the potassium concentration inside the cells.
Again -- this is critically important to an understanding of brining -- if the percentage concentration of sodium on the outside of a cell is higher than the concentration of sodium on the inside of a cell, then free water molecules will pass from inside the cell, through the cell membrane, and into the intracellular space. McGee at 544.
The process of osmosis is a requirement for the survival of living cells, because it regulates the concentration of minerals. But osmosis is a chemical property and does not require living tissue in order to operate. Thus, osmosis -- the diffusion of water across a cell membrane -- works in non-living tissue and is the basis for brining.
Brine is a concentration of water and salt, typically in the ratio of 16 parts of water to 1 part of salt (such as 2 gallons of water with 2 cups of Kosher salt).
Brining operates on the principal of osmosis, as explained above. The brining liquid has a higher concentration of sodium than the meat's intercellular spaces. In a series of reactions, both the number of sodium molecules and the number of free water molecules increase in meat's intercellular spaces, and the sodium concentration increases in the meat's intracellular fluids.
As the meat remains in the brining solution for many hours, the process of osmosis causes the free water molecules in the intracellular fluids to exit the cells. Contrary to popular belief, sodium does not pass from the brining solution across the cell membrane into the cell, but there is some increase in the sodium in the intercellular spaces by the simple process of diffusion.
Therefore, during brining, the free (unbonded) water molecules inside the cells move through the cell membranes and exit out to the intercellular spaces. This appears to accomplish exactly the opposite effect that is intended by brining, because this would seem to make the meat drier. But the process continues . . .
As the free water molecules leave the meat cells, there is an increase in the sodium concentration inside the cells. The concentration increases because of the loss of water, not because of a gain of sodium. As the concentration of sodium increases, the sodium "cooks" the intracellular proteins, denaturing them. The denatured proteins then cross link and bond with the free water molecules -- remember how the raw egg turned white -- forming a tight molecular bond between the protein chain and the water molecule. Now, the water is trapped in the protein and is no longer a free water molecule, so these water molecules will not exit the cell. This cross linking of protein and water molecules means the cells will not break up and lose their moisture at the normal temperature of unbrined meat -- higher temperature than unbrined meat.
In summary, the brining causes an increase in the cellular sodium concentration, which denatures the proteins, which cross-link to form tight bonds with the previously free water molecules, which resist breaking apart except at a higher-than-normal temperature.
Brining thus increases the temperature at which the protein and water bonds will break and release their bound water molecules. In other words, brining causes some free water molecules to exit the cells while the remaining water molecules are trapped and bonded tightly to the denatured protein chains, which remain stronger with the presence of the increased sodium concentration. As a result, the temperature of the so-called second sweat will increase from 140°F to perhaps 160°F. As a further result of this increase in temperature, the meat will cook but still retain the moisture that would normally have been lost.
There are several popular misconceptions about brining:
These are misconceptions, but they are only wrong by a little.
Sodium in meat cells
As explained above, the brining solution by the process of osmosis causes intracellular free water molecules to exit the cells. However, brining does not cause sodium to enter the cells. It only seems so.
There is no diffusion of sodium into the meat cells, because the cells themselves already contain a high concentrations of sodium. Even very concentrated brining solutions will be less concentrated than the intracellular fluids.
However, as the intracellular fluids lose their free water molecules, their concentration of sodium increases, because of the loss of water. Therefore, the cells seem to have increased their sodium content, but this is only an illusion.
In the case of the intercellular spaces, however, brining does cause an increase in sodium concentration, not by the process of osmosis (there are no cell membranes) but by the process of diffusion.
It is true that brined meat will be moister than unbrined meat, but not because of the added water.
Yes, it is true that brining meat increases the water content of the meat. In fact, a brined turkey will gain about 20% in weight. For example, a 15 lb. turkey will weigh about 18 lbs after brining overnight. However, virtually all this extra water is contained in the intercellular spaces and will be lost when the internal temperature reaches 120°F, during the so-called first sweat. By the time the meat is cooked, all of this added water (and much of the natural water) will have left the meat. Therefore, the water added by brining will not remain during cooking to make the meat moister.
The brined meat is moister because of the added salt in the intercellular fluids. As explained above, heat makes proteins denature and coagulate. Without brining, the cells disintegrate and release their intercellular fluids at a temperature of 140°F -- the so-called second sweat. However, with brining, the increased sodium within the cells causes the cells to remain intact until the internal temperature reaches 160°F. This means that the cellular fluids are retained in the meat, so the meat is moister.
Brining does not cause the meat to be more tender, at least not directly, in the way that a marinade does. Brining makes three changes which seem to make the meat more tender:
Brining increases the temperature at which the meat cells like collagen will break down, and this in turn keeps the meat from losing the intercellular water molecules and drying out. Thus, the meat is moister.
In addition, the increased water retention lubricates the individual muscle fibers, which improves the texture of the cooked meat. Finally, the increased sodium improves or brings out the flavor of the meat.
The combination of meat that is moister, has a better texture and is more flavorful seems to make the meat more tender, but this is not really so.
Brining red meat
Brining does not produce a desirable result in all meat, especially red meat.
With brining, the flavor change in red meat produces a ham-like flavor. While desirable in smoked pork chops, ham, bacon, corned beef, prosciutto, and pastrami, this change in the meat's flavor is not appropriate for traditional forms of barbecue meat, such as pork ribs, pork shoulder and beef brisket.