Science with Richard Bleil
Although this is a story that I believe I’ve written about previously, I was recently reminded of it so, here I am, writing on the topic of eating raw pork again. Yes, raw pork. Imported. From overseas. I want to say Libya, but I’m not certain.
See, it was so long ago that I cannot recall which friend brought it to me. I met him in graduate school in Boston, and when I began my first post-doc stint in New York City he wanted to visit. That was fine with me; I gave him a place to rest his head for a few nights. I was just being kind, and certainly didn’t expect anything in return, but he brought me a two-foot long salt-cured pork.
Salt-cured means that no heat was used to prepare it. Instead, for all intents and purpose, it was just stuck in a barrel of salt and forgotten for quite some time. Or brine. I could have been brine.
Does it sound familiar? It should. This is also how sauerkraut and pickles are cured. It’s a principle called “osmotic pressure”. As it turns out, we, you and I, and pretty much everything alive (except for viruses, although there’s still the debate as to whether nor not viruses actually are living) is made up of semi-permeable membranes. We’re walking filters. Our skin, for example, lets oxygen and moisture in while blocking organic toxins.
Basically, every cell membrane is the same. It’s designed to let water and other nutrients and minerals in depending on the need of the cell. Diffusion is the flow of solutes (that is, substances other than water) through the cell membrane, and osmosis is the flow of water. Osmosis is always the flow of water from a region of low concentration to a region of high concentration.
It might seem like an odd concept to dry something out by adding a water solution like brine, but brine is an extremely high salt concentration. Because this concentration is so much higher than the cells in the pork (or pickles) that it literally draws water out of the cells causing them to dehydrate. No, they won’t dry completely; we’re not talking about making jerky, but they will dry to the point where the cells are no longer able to live. This doesn’t happen just to the cells of the food, though, but also to the cells of any bacteria in the food that can cause food poisoning. When you cook food, you heat it up to kill the bacteria by causing the proteins to denature and disrupt the chemical processes of metabolism. In salt curing, you deprive it of the water it needs to live.
By the way, this is the same reason that honey, or sugar for that matter, don’t need to be preserved or refrigerated. Honey is basically a solution of extremely high sugar concentration, and while it is an excellent source of sugar necessary for survival, it is also such a high concentration that, through osmosis, it draws moisture out of anything that comes into contact with it and kills it. No bacteria grows in honey because cells cannot survive in it.
The opposite is also true. If you over-water a plant, for example, you can kill it. This is because so much water is going into the plant through the root system, and basically flooding out the extracellular space, that the cells end up having too much water forced inside. This literally dilutes the cells to the point that they cannot survive and may even explode.
I have a friend that is a survivor of a rare condition called “hyponatremia”. Runners sometimes get this if they drink water rather than an energy drink of some form. As the athlete sweats, s/he is losing salt. When you drink plain water, you’re replenishing the water but not the electrolytes (a fancy chemical word meaning “salts”). This forces too much water into the cells, in particular in the brain, causing the electrolyte concentration in the cells too low to be able to function. The end result is that the cells will die causing brain damage and death. Drinking an energy drink, on the other hand, also replaces the electrolytes. This means that even though the amount of moisture in the extracellular version is increasing, the proper ratio of electrolytes will be maintained. With proper electrolyte concentration, the fluid becomes “isotonic”, or the same concentration as within the cell. When this happens, the “osmotic pressure” (that is, the force that causes the water to flow through the cell membrane in either direction) will be zero, meaning no excess fluid will flow into or out of the cells.
I’ll be honest; I love salt-cured foods. Pickles, kimchi, olives, sauerkraut, pickled herring, it’s all delicious.
Bleil's Banter 