Its use is a tiny amount and is also used in making some beers and wines to reduce foam at the onset of fermentation. Silicone dioxide, a similar product, is also added to salt and many foods for reducing caking and clumping. The product you mention is inert and will not affect flavor, color, or the life of the product you add it to. You do need to follow the directions to add the proper amount. This is NOT a preservative in any case. If its related to xanthan gum or guar gum, it is a biological byproduct. A trace of foam in jellies is OK too. If its low sugar and you use Pomona pectin, that requires a form of calcium to set, as opposed to being dependent on sugar. A teaspoon per batch of 5-6 cups isn't too much and I do believe its use has been going on for at least 20 years or more, just like silicone dioxide. Some carbonated beverages use a 'header' that creates foam, like in the case of root beer. Also, once regular beer is fermented and hops are added and its filtered, it too gets a 'header' added to help give it a foamy head when its poured out.

Ever heard of 'artifical preservatives'?? what are they, in relation to REAL preservatives??

Personally, I wouldn't use it. Buying at farmers markets is perceived to the public as being as close to growing your own organically as possible, with or without Certification. Putting that ingredient on the label might stand out as being commercially prepared.

Although I still have some mold retardents and gums from our prepared salad business I don't use them anymore, except for titanium dioxide and taraganth gum for edible cake decorations. I have teased people when they ask if edible and I reply yes it is, even has sunscreen in it, lol. (they won't eat them then)

Jellies more so than jams sometimes have a slight foaming for me. Now that I don't add butter to reduce I fill all jars wipe the lids, rims. By the time that step is done if there is any foam it has formed a skin and I quickly skim the tops of the jelly in the jars to remove any foam. I only do this to the jars I am entering in competition for giving away no one has ever mentioned a foam issue.
I list expiration dates of 6 months to a year or less if I haven't tested.

Why would you want them to keep something for 2 years? If it expires sooner and you have a winning recipe they will be back alot sooner and you will have repeat sales.

Farmers markets vary greatly. To be certified 100% organic is not cheap and requires a lot of extra work for any size farm. Many farmers are close to that level, but few can remain 100% organic, only because the land acreage can vary. In the case of the item you mentioned, it could be mentioned in the ingredients, then also described as an anti-foam agent. I doubt if most people would even bother to look at the ingredients list. As mentioned, its use has been for many years by the commerrcial industry and it will not affect taste, smell or any other normal character for any jellys or jams. Refined sugar, in its normal process, requires many nasty chemicals (sulfur, lime) to get it to the white granulated stage we see in stores. If all the chemicals were mentioned in sugar manufacture and refining, it would be a long list, and probably scare off most anyone.

I see no degradation of properly home canned products. If I were to throw out my stuff dating back 2 years, that would wipe out all my tomatoes, most of the pickles, and 90% of my jams and jellies. Well over 200 jars in total. I am not about to do that with my canned foods as they are as good today as the day they were made. The ONLY issues are darkening color for some fruits, and cukes getting softer after that length of time. In either case, they are not poison, and not unappetizing to me. If we followed the rules of 6 months, we would have to do all our canning and date each and every jar, then toss them out if the dates went past 6 months. Way too impractcal. Who can really say what an expiration date can mean. Many commercial products contain so many 'stablizers' and preservatives, they could last a century. I just cooked up a 2 pound bag of shrimp that has been double bagged in my freezer since 2004. It has no freezer burn or any loss the flavor or texture. Even after I compared it with some shrimp I just bought and also cooked up seperately. Properly packaged, even frozen foods can last a long time. Around here, there are no farmers markets for many miles, so my summer garden sales and garage sales do very little business.