By Richard E. Bleil
Ever eat pork raw? I have, and it was amAZing!!!!!!!
Don’t go out and start eating raw pork. This is not likening pork to steak tartar, which is an old dish that is basically raw steak. No, this blog is actually about salt curing.
Many years ago I was living in an apartment in the upper east side of New York City. A friend of mine, a graduate student that came from the middle east, decided to visit me from Boston where we were in school together. He brought a gift, a three foot long salt cured pork sausage. He wouldn’t share it with me, so I waited until we parted before cutting into it. I didn’t eat it all in one sitting thought. There were three slices left the next day.
When we cook pork, along with making it delicious, we want to be sure that we kill all of the bacteria that cause illness. There are two reasons that this works; the bacteria cannot survive at elevated temperatures, which is why we want to be sure the inner temperature reaches a certain point. But, as we are cooking it, not only are we increasing the temperature, but we are also driving off water.
With the possible exception of viruses, every living things (and viruses may not be…an interesting topic for a future blog post) required water to live. This includes bacteria.
In salt curing, no heat is (usually) used. However, the purpose of salt curing is to remove water from the pork (or bacon or anything else being cured). Nothing can live (again, with the possible exception of viruses if they are alive) if the water content is too low.
The reason being a colligative property called “osmotic pressure”. You’re familiar with colligative properties; these are properties of solutions. It’s why we add salt to ice to make it melt, and to water so it boils hotter. Mixing antifreeze with water protects the engine by both making the coolant boil at a higher temperature in the summer and freeze at a lower temperature in the winter.
Osmotic pressure is the flow of water through a membrane, like a cell wall. It shouldn’t surprise you that when in water, the water will flow into cells. We see this in plants; when they are not properly watered, they wilt. Adding water kind of fills them back up, like a balloon being blown up and firmer as a result of the addition of water. The opposite is also true.
When pork is put into salt, the water is literally drawn out. This force is measurable; it’s actually a force, like gravity is a force. The pull of water out of the pork is called “osmotic pressure”. Once the water level gets low enough, the water is also pulled out of the bacteria, causing the bacteria to die.
As it turns out, the salt need not be dry for this process. For example, pickles are made from soaking cucumbers in brine solution. Brine is just a water based solution that is very high in salt. Because the concentration of the salt in the brine solution is significantly higher than in, there will be osmotic pressure, essentially a force that is trying to make the concentration inside the cucumber the same as outside, by drawing water out. The cucumber is plump and filled with water. As the water is pulled out, this large plump cucumber begins to shrink as it loses the water content. Typically we don’t worry about bacteria in cucumbers, but the process of pickling would kill any bacteria present.
Honey is a very interesting solution. With other components in it, sugar is essentially a concentrated solution of sugar in water. The bee produces it by putting sugar solutions into the open combs of the hive. They leave the combs open, and as the water evaporates off, the level of solution will decrease. Bees continually refill this, thereby adding more and more sugar. Eventually the sugar solution begins to become very thick and viscous (slow moving) because the concentration of sugar is so high.
The first thought you might have is that a solution of sugar and water seems like the ideal place to grow mold and bacteria, but, we don’t refrigerate honey, we don’t rush to eat it, and we never worry about it. The reason is very simple; the concentration of sugar in the honey is so high that the osmotic pressure immediately draws water out of any microbes that come into contact with it, killing the microbes. The honey, then, is sterile.
See, colligative properties are independent of the identity of the solute. A high concentration of salt (brine) creates a high osmotic pressure, but so does a high concentration of sugar. You might be wondering, then, if salt is the only choice as ice melt, and the answer, frankly, is “no”. You could just as easily spread sugar on the ice and it would still melt, except for a couple of problems. The nature of salt means you need less salt, so you would have to add more sugar, and the salt will not attract animals to eat it.