Because cantaloupes have high pH, my guess is that the red speckles you’re seeing in a layer on top of your wine are bacteria colonies and no, they are not to be expected. According to a fruit pH chart I found online from Clemson University, the pH of cantaloupes usually falls in the range of 6.1–6.6. The pH of water is 7.0, and the pH of most table wines made from grapes fall in the 3.3–3.7 range, so are much more acidic than melon juices. Bacteria tend to thrive in a higher pH (lower acidity) environment, which is one part of the reason most wine in the world is made from grapes, whose lower pHs keep spoilage bacteria at bay better (alcohol being the other part of the equation). Wine made from grapes just naturally “happens” better than wines from other fruits, which sometimes need hefty acid additions.
As the article on making melon wines mentions, because melons grow on the ground (as opposed to grapes that are up off the ground on vines), they can pick up a lot of soil-borne microorganisms. Cut into the skin and you’ve just introduced potentially harmful bacteria into the fruit you’re about to press for the juice to make your wine.
Do you need to throw the wine out? Not necessarily, but you might want to be careful if your pH is high and your wine is still in the juice stage. Foodborne bacteria like E. coli and Salmonella can survive on cut watermelons and cantaloupe, and in the raw juice. Luckily, a pH under 4 will inhibit the growth of just about all food-poisoning bacteria and increasing alcohol levels will also help eliminate them. Dr. Linda Bisson, Professor of Enology when I was a student at UC-Davis often told her classes, “No human pathogen can survive in wine.” There’s a reason that drinking wine was safer than drinking water in the Middle Ages and also why wine was used by ancient civilizations to disinfect and clean wounds. However, cut cantaloupe and raw cantaloupe juice can harbor bacteria harmful to humans so do be careful and practice smart food-handling practices when using them in meals, juices, and in winemaking.
Foodborne bacteria like E. coli and Salmonella can survive on cut watermelons and cantaloupe, and in the raw juice.
Keep an eye on how your wine is progressing because surface-growing bacterial colonies are rarely good news in winemaking. You also could be experiencing a flush of spoilage yeast; the fact that you’ve got colonies growing on the surface also leads me to include aerophilic (oxygen-loving) “film yeast” in the spoilage-organism suspect pool. “Red-colored speckles” doesn’t sound like any common winemaking yeast or bacteria I’m familiar with and it’s very possible they (and other organisms you can’t see) may throw off the flavor and aroma of the finished product. Melon wines are ephemeral products, with the heady aromas we love dissipating very quickly during fermentation. What remains often just seems like the “ghost” of the fruit, even with sound bacteria-free fermentations. This will be even more so if you’ve got any kind of spoilage organisms in there doing their dirty work.
To avoid surface-growing film yeast (and also spoilage bacteria) next time, make sure your sanitation procedure is top-notch and get the alcoholic fermentation going right away with a strong strain of yeast so you get a protective layer of carbon dioxide formed on top of the surface. I also don’t recommend using any kind of coconut meat, milk, or water in winemaking as it will contain fat. Especially if your coconut water is the kind sold with small pieces of coconut pulp in it; those little bits will float to the top, forming a perfect little raft for spoilage organisms to grow on!
If your wine goes dry and you still like how it smells and tastes, I recommend sterile filtering it, if possible, with a unit like those made by the popular Buon Vino brand. They can be spendy so see if your local home winemaking supply store rents filters or if a local home winemaking club has one you can borrow. Filtration (if done with filtration technology that is 0.45 micron sterile or “nominal”) will exclude all yeast and bacteria from your wine, which will help set it up for sound aging. Be sure to adjust the free sulfur dioxide of your wine to around 25–30 ppm (there is a great sulfur dioxide calculator at winemakermag.com/sulfitecalculator to help you do that) so you know your wine will be further protected from oxidation and microbial spoilage during aging. Speaking of which, melon wine lacks the tannins and antioxidants that grape wines naturally have, so it’s recommended to drink them within a year. I wish you luck!
