Part I - Vacuum Sealing - A bit of Physics
Okay, let’s learn some quantitative physics about what really happened. Those bubbles were simply the result of some of the liquid portion of the jar contents boiling off as water vapor, even when the product was pre-chilled in the refrigerator, because of the high vacuum conditions. Thus, the explanation for what happened is that the boiling point of water becomes amazingly low under high vacuum. We all know that water boils at 212º F at normal atmospheric pressure of 14.69 pounds per square inch (PSI) (or 29.92 inches of mercury in a Torricelli barometer) at sea level, but when that pressure is severely reduced to near total vacuum conditions the boiling point changes significantly.
Specifically, refrigerated water at 40º F will boil if the vacuum sealer vacuum level (as shown on the vacuum gauge) is 29.17 inches of mercury, which is down around 0.37 PSI. At a vacuum level of 29.76 inches of mercury water will boil at 30ºF, which as you will note is below the normal freezing point of water (32ºF) at normal atmospheric pressure. When you dial in the effect of having the water mixed with solids and semi-solids in the foods we try to vacuum seal, we find (for other physical reasons I will not cover here) that the water portion will boil at slightly higher temperatures than what pure water will boil under vacuum conditions. Finally, the type of food being vacuum sealed affects the process as well. Salt in the food tends to depress the freezing point and slightly increase the boiling point. What fun!
Sooo … can we vacuum seal liquids and sauces and dressings in canning jars and be successful, and if so, how? Here is one idea I have yet to try with canning jars, but one that I know will work. Put the canning jar with product at least 1 inch from the top and with the canning jar lid and ring on it loosely into a taller hard-sided container (glass or plastic) that will close/seal tightly, and to which you can attach the vacuum line from the vacuum sealer. When you vacuum seal, none of the product will exhaust into the vacuum line, because of the large physical displacement of the product surface from the point of maximum suction. The product will still "boil" slowly and develop the "bubbles" but it will not overflow the canning jar, and after vacuum sealing is complete you can make the product appear normal again by gentle tapping against a soft surface to get the bubble areas to rise to the top. This is similar to getting air bubbles out of cake batter. The moral of this story is clear. Be aggressively determined to be successful, find out what is really happening and use your brainpower to figure out a workable answer.
For every funny story about screw-ups I like to tell one about successes you can have if you "think outside of the box," which simply means use your imagination to develop novel solutions to seemingly intractable problems, similar to the above story. My story here is what I learned from reading an obvious fact and not liking that fact, and then doing something different to make the fact irrelevant.
Try to vacuum seal a loaf of bread or a pastry in a plastic vacuum sealing bag and you will see it collapse into a small clump of useless gunk. Taking away the air from the inside of the soft bread/pastry by using a vacuum sealer, while allowing a flexible bag to compress it from the higher air pressure outside, and the loaf of bread or pastry is wrecked. So, does that mean we can’t vacuum seal soft products like bread? No, it certainly does not mean that at all. Yet, makers of vacuum sealers and other literature do not tell you how you can successfully vacuum seal things like a loaf of bread. The secret? Put the bread or other soft baked item into a strong plastic container that will not collapse. Put that container into a vacuum sealing bag and vacuum to your hearts content and let it seal. Voila, you have preserved bread/pastry without freezing or any other physical storage procedure. When you later break the vacuum seal to use the bread it simply gets the air it needs and holds its original shape. I know this works very well as I have done it many times.
Recently I saw an ad and a video for a new product named, VacuVita®, on the Internet. I was most pleased as that product does exactly what I was attempting to do by using hard sided containers with vacuum sealing. You might guess that I ordered the complete kitchen set of that product, and it will be shipped sometime in September 2013. I will work with it and provide a review in Food Nirvana so that you will know if it works as advertised and if I can apply some of my own ideas using it, like vacuum sealing liquid products in canning jars without the problems of using a close proximity vacuum line.
Okay ... it is time for a Vacu Vita update. Wow! This is December of 2016 and I got my full Vacu Vita product set shortly before Thanksgiving. That was a long wait. On the other hand I now have a very high quality product made to European appliance standards, which are vastly superior to what is sold typically in the USA. Marie and I learned that important fact back in 1998 when we lived in Switzerland. I still use the powered appliances we bought there (they last!) and we even provided 220V power to our kitchens to be able to do so. Well, the Vacu Vita I received was built to operate on the 110V power we have in the USA, so you can get one and not worry about needing a special high voltage circuit for your kitchen. I hope you buy one. The product even comes with special reusable vacuum sealing bags perfect for doing sous vide cooking. I am delighted with my Vacu Vita!
Part II - Food Preservatives - A bit of Chemistry and Biology
Food manufacturers use a variety of chemical preservatives to provide their products with good shelf life, ergo, products that stay fresh and tasty and do not get moldy or otherwise spoiled. Breads and other pastries are a good example. Likewise lunch meats and many beverages and bottled liquid products like pancake syrup. Almost all products other than fresh fruits and vegetables have one or more types of preservatives, and often even some fruits and vegetables are sprayed with an antifungal product to avoid surface contamination and mold or rot. Exceptions are found in canned goods that tend not to deteriorate. Two common preservatives are potassium sorbate and sodium benzoate. Potassium sorbate is used at a concentration of 0.1% to 0.3% by weight of the product, and you can buy it easily and cheaply via Internet vendors or in stores like Wal-Mart®. Similarly, today sodium benzoate is easily purchased via the Internet, but I have a story below that describes the steps I had to take when it was difficult to obtain sodium benzoate powder. You are about to get a science lesson and I hope you appreciate/enjoy it.
This section is a story about finding sodium benzoate online at a time when it was not commonly available to consumers. It was in concentrated liquid form and the seller would not disclose the concentration ... thus I determined it myself by using a simple scientific method. Note that now you can simply buy pure sodium benzoate powder via Amazon®. But take time to read the story, for it will give you insight for other potential applications with other food preservation chemicals and food additives.
I was delighted to find that I could buy concentrated sodium benzoate solution from the people who sell snow cone syrups, Koldkiss®. Sodium benzoate is used as a preservative for many foods, like pickles, soft drinks, and, well the list goes on and on. The proper amount to use is anywhere from 1/20th to 1/10th of a percent by total weight of the product and the liquid that contains the product. Also, sodium benzoate will not work effectively unless there is some acidity in the liquid, like that provided by vinegar in pickle brine. The optimal pH is 4.5. Given the proper conditions sodium benzoate can keep products in glass jars from spoiling after being opened, easily for a year, as long as they are kept refrigerated and resealed properly with the lids. That means many products I make, like tomato juice, which is naturally acidic, benefit from the addition of sodium benzoate, such that they can be refrigerated after vacuum sealing with no concerns about spoilage or fermentation. Thus, canning is unnecessary. Another example is the Hot Giardiniera Condiment used on steak sandwiches and subs. Yet a third example is my hot habanero sauce.
Now I get to the science part. Koldkiss® provides instructions to vendors who sell snow cones regarding the use of concentrated flavor syrups, sugar, water, concentrated sodium benzoate solution and their fruit acid product that is used to acidify the final syrup that will be dispensed onto shaved ice. As most snow cone vendors are not educated in chemistry the simple instructions from Koldkiss® are just what they need. But now a person like me comes along and I need to know the exact concentration of the sodium benzoate solution so I can know precisely how much to use with each of the food items I prepare for long term storage, either in a pantry or in a refrigerator. Koldkiss® declined to share that information with me so I had to use my education and common sense to outwit them and determine for myself the precise concentration of sodium benzoate in their concentrate product.
Thus, the following discussion is about what I did and what I learned. First, I dispensed exactly one tablespoon of their liquid concentrate into a small weighing dish used with my very sensitive electronic reload scale that I purchased from Cabelas®. I weighed it and the total weight of the dish and the contents was 13.25 grams. I then placed the dish in a 160 degrees F oven to evaporate the water from the dish. Once the water was gone I let the dish cool to room temperature and then weighed it again. That time the weight had been reduced to 9.65 grams. Finally, I rinsed the dry sodium benzoate from the dish and dried it completely. I then weighed the empty dish and it was 7.40 grams. Now I had all the information I needed to directly calculate the concentration of the Koldkiss® product.
The total weight of 13.25 grams less the weight of the empty dish, 7.40 grams, yields 5.85 grams of weight for one tablespoon of the concentrate. The weight of the dried product in the dish, 9.65 grams, less the weight of the empty dish, 7.40 grams, yields 2.15 grams of sodium benzoate in one tablespoon of the concentrate. Thus, the weight of the water in one tablespoon of the concentrate is 5.85 grams less the 2.15 grams, or 3.70 grams.
Two tablespoons is one fluid ounce. Thus, each fluid ounce of the concentrate contains two times 2.15 grams or 4.30 grams of sodium benzoate. That is precisely the information I needed to know how many fluid ounces of the concentrate to use in a batch of whatever product I happen to be making. For example purposes, assume I have a mixture of product and liquid that weighs ten pounds. Lets assume I want to use sodium benzoate at the rate of 1/10th of one percent by weight. Thus, 10 lbs. divided by one thousand gives the right amount needed in pounds. That number is 0.01 pounds. Now, knowing that one pound is 454 grams (of any product) I multiply by 454 and my result is 4.54 grams of sodium benzoate as the right amount needed. Thus, I know I need a bit more than one fluid ounce of the Koldkiss® concentrate to add to my product. Specifically, 4.54 divided by 4.30 yields 1.056 fluid ounces.
Now I can multiply the weight of one fluid ounce of the concentrate by 1.056 and know the exact weight in grams of the concentrate I need to measure out and use. Thus, 5.85 grams per tablespoon of the concentrate times two tablespoons per ounce yields 11.70 grams per ounce. Now I multiply the 1.056 fluid ounces I need by the 11.70 grams per ounce and I find that I have to dispense 12.36 grams of the concentrate solution into the weighing dish, and then dispense that liquid into my product and mix it thoroughly. So I use my reload scale to measure out 12.36 grams of the concentrate solution and I don't have to think about trying to do liquid measures down to the thousandth of a fluid ounce. Easy, wasn't it?
Most of the time you will never come across a situation as detailed and necessary as what I had to do to use the Koldkiss® product. But this example shows just how important it can be to dabble in science to get what you want. There is also the consideration that in doing my experiment I might have made an error in measuring of undetermined amount, or an error in my calculations. In science one of the ways we deal with those possibilities is to repeat experiments looking for precision in results. Given the doing of multiple presumed identical experiments we then compare the results and quickly determine the reliability of the experimental procedure in terms of precision. If the results vary widely then the procedure isn't very good.
Accuracy is a related but different matter. For example, suppose the Koldkiss® folks put a second chemical in their concentrate solution besides the sodium benzoate, perhaps to help keep the sodium benzoate in solution. What that would mean is that the weight of the dried product in my experiment would be that of the sodium benzoate plus that of the other dried chemical or chemicals. That means the actual concentration of sodium benzoate in the solution would be less than what I determined. I could do other experiments to determine if that situation exists, but in this case the Koldkiss® folks declare that the only ingredients in their concentrate are water and sodium benzoate, so we put that problem to bed (maybe).
Here is one very important additional point. Koldkiss® could change the concentration of their sodium benzoate solution at any time and not notify their customers of the change. Why might they do that? One reason could be that by doubling the concentration they could package the solution in 500 ml bottles instead of 1 liter bottles, thus saving some money. They would at that point change their instructions to snow cone vendors regarding how much of the concentrate to add to a batch of snow cone syrup. The rest of us who are using the sodium benzoate to do other things than make snow cones would not be any the wiser and we could mistakenly use too much sodium benzoate in our food preservation steps in various recipes. Thus, ALWAYS test the concentration of the sodium benzoate solution when you purchase a new supply, in the manner I explained above, doing what I did.
We still have the issue of how accurately I could measure and then dispense exactly one tablespoon of their product. As I am sure you know, measuring spoons are rather pathetic when it comes to dispensing precise quantities of anything. In a laboratory environment a liquid product would typically be measured and dispensed using either a pipette or a burette, which are finely calibrated glass tubes that are used to hold and then dispense precise amounts of a liquid. Yes, you can purchase products like pipettes and burettes from companies like Fisher Scientific® if you really want to get into this aspect of food science.
Check out the simple recipe for strawberry preserves at the end of this section.
Okay, that is enough science for today! Class dismissed!
Summary:
I conclude this section with the simple idea that your income can go further and your quality of life can get better if you will learn to take advantage of modern food preservation and processing technology. All you have to do is use your native intelligence and have some curiosity and sometimes the willingness to experiment. The rewards are great and your inner feeling of independence and satisfaction will put a smile on your face often. You are in charge.