I've noticed that commercial gummies do not melt, even when they are left in the sun, while home made gummies melt even at room temperatures sometimes.
What is the secret ingredient? Sugar?
I've been making a lot of room temp gelatins lately; not gummybears, something else with a bit lower gelatin concentration. The secret ingredient seems to be time. The first day, things are pretty jiggly, but even when hermetically sealed, things get tougher and tougher over a course of about three to four days. I expect it's some colloid maturation process involving random chains finding their best fit over time. Don't quote me on that, but the same sort of thing commonly happens on a faster timescale with gluten maturation in bread dough. A few hours in the fridge can speed up firming, but I'm not sure you end up with the same final gel structure that way.
I just checked the ingredients on one of the Vitafusion bottles I have and I believe the secret ingredient to "non-melting-gummies" is WAX. They use either beeswax or carnauba wax. Other than that they are pretty much like homemade gummies with the exception of using glucose and sucrose syrups which I don't believe would make a difference in whether they melted or not. So, I would make up a melted beeswax and dip each gummy in that. Unfortunately, you would not be able to polish them up in the big drums that they use so that might be an issue. Maybe color the wax with a natural food coloring.
You have to dry the gummies for 3 days. Start with so much gelatin that it's just slightly difficult to eye dropper into the mold, then back down from that. Let them harden overnight in fridge, spray coconut oil on hands and on back of gummies in the mold, then rub them with your hands as each one is removed, making sure they are coated with the oil, but very thinly. Dry them like that, individually set apart on parchment paper. Where I make mine, it's always 85F. At that temp, the 1 gram (1ml) gummy molds won't droop (much). Just blow on them with a little fan. Cold dry air from an airconditioner is slower, just use the room temp air.
Larger gummies will droop out of shape using this method, so dry them in the fridge. Takes 3 times longer, but gummies fully exposed in fridge can lose 2-3% moisture per day. In room with fan, as much as 10% moisture per day.
After drying the gummies until they are slightly firmer than Haribo, recoat with oil using your hands.
They'll spoil easily unless you add Potassium Sorbate. Get that at a beer brew supply shop, along with corn sugar which can be used 50/50 with regular sugar to help prevent crystalization.
Check web for amount of Potassium Sorbate to use, but it's very small. And considered so safe, it's ok to use on "organic" candies.
With proper sorbate, and sugar content above 55% by weight, you can stick them in a mason jar with some moldy (fully furry) gummy bears next to them, and they won't spoil even after a full week. Not sure beyond that, I ate the little guy to see if he picked up moldy taste. Nope.
The "secret" component of commercial gummies is gelatin and if we take a look here especially the Production section where it says commercial gelatin is comprised of animal products such as animal bones, bovine hides, and pig skin. And from our knowledge of basic chemistry we know that bones, skin, and hides don't readily melt in room temperature or when they are kept under the sun. At the same time there are gelatin that are made for vegetarians and instead of animal parts they use a plant called Konjac which doesn't readily melt either.
I've been experimenting with gelatin alternatives to make vegan gummy bears, and in my research I've noticed the temp influenced changes for different ingredients:
gelatin (melting point): 95F / 35C agar agar (starts to lose firmness): 149F / 65C agar agar (melting point): 185F / 85C konjac (melting point): 217F / 103C
I have also read that too much water in the mix can cause it to "bleed". You can get reduced water in the heating method, which means your final "goop" that you pour into molds should be high in viscosity to reduce this bleeding effect on a hot day. But then usually that means the sugar concentration will be much higher, so some people use maltodextrin (a glucose) as a portion of your sugar content as it is less sweet than sugar.
I don't know what the secret ingredient is, but I can guess, based on ingredient lists I've seen. My guess is corn syrup that has been heated to make it thicken, perhaps combined with gelatin or something to make it return to its shape after pressing on it. I could be wrong.