It seems like you already have the acidity-adjusting situation well in hand — this is often one of the areas in which non-grape wines meet their downfall. As you already have realized, the first step to making great wines from non-grape sources is to recognize that these materials are different from grapes and will usually (though not always), lack the necessary acidity, sugar content and nutrient balance to result in a pleasing, balanced, ageable and microbially-stable beverage. You are doing yourself and your wines a great service by using an acid test kit, coupled with your natural sense of taste, to adjust the acidity appropriately.
When dealing with any kind of non-grape material for winemaking, it’s important to remember the chemistry parameters of what will, hopefully, yield wine as an end product. The starting material (juice, must or composed “brew” of non-grape items) of most table wines (we’ll leave the discussion of dessert, sweet, fortified or sparkling wines for subsequent columns) made from grapes fall within the following ranges: Titratable (or Total) Acidity: 5.0–8.0 g/L, pH 3.10–3.65, Brix (sugar levels) 22.0–26.0.
Due to style desires as well as practicality, however, non-grape or country wines are often started with lower sugar levels and will result in a lower eventual alcohol content, like 9.0% or 10.0%. This is perfectly fine, though the wines may not age as long as a higher-alcohol table wine.
Once you tackle the above parameters and adjust your country wine’s starting material accordingly, I recommend that you think about adding some tannins to your wines, especially if you are trying to mimic a red wine style using blackberries, blueberries or elderberries. Tannins, naturally present in abundance in all grape wines, even whites, are natural antioxidants. They help a wine age longer and can provide sensorial balance and a sense of grip on the tongue. Many home winemaking stores and catalogues carry some kind of tannin mix and there has been an increasingly sophisticated selection available through commercial winemaking suppliers like Scott Labs, Gusmer Cellulo and Vinquiry.
Grape juice concentrates can also be a balanced and authentic source of tannins as well as a host of other goodies including amino acids, aromatic compounds and trace nutrients that will all contribute to better wines. Instead of using table sugar, honey or other fruit juice concentrates, I suggest getting a portion of your wine’s sugar from grape juice concentrate, red or white, depending on what kind of wine you’re hoping to make. These can be easily mail-ordered or ordered online and shipped to your location. I recommend brands that don’t contain potassium sorbate, which can inhibit yeast. You may also want to try using a yeast nutrient like Superfood (sold by American Tartaric) or other blend sold by the above tannin suppliers. These nutrient blends will help to ensure that your yeast have all of the micro and macronutrients they need for a healthy and happy fermentation, which always will lead you to better wine.
When making non-grape wines, besides mimicking the starting material of grapes as much as possible, you need to also be sure to treat the finished wines with much care and respect. Very often, the delicate aromas, light colors and ephemeral tastes of country wines won’t age as well as a grape wine would. For this reason, it’s critical to store your finished wines well away from heat and light. It’s also important to try to store them somewhere where the temperature won’t widely swing from one extreme to another. Interior closets away from outside house walls can be great for someone lacking a cellar or basement.