Welcome to the world of cider.
I guess that when many of us made our first cider we expect to get an apple flavored alcoholic beverage, but instead got something that is dry, tart, and “arrgh”, what is that? ...tasting not at all like some of the commercial ciders which are modified to “improve” the flavor.
To paraphrase the cider guru, Andrew Lea… “wine doesn’t taste like grapes, nor beer like barley, so it is illogical to expect cider to taste of apples”. However, all is not lost since the cider flavor is easy to modify, but first it is useful to understand what cider is.
Cider is fermented apple juice where yeast converts all the sugar into alcohol and CO2, leaving water, alcohol and flavor compounds.
The flavor of the original juice basically comprised three elements, sugar, acids and tannins (the sugar provides sweetness, the acids tartness, and the tannins bitterness and astringency. So, to modify the cider flavor, it is typical to add and balance some or all of these elements.
As a guide…
Adding sugar will simply produce more alcohol and CO2 (which escapes into the atmosphere) unless residual yeast is inactivated by heat or chemical pasteurization to stop any new fermentation. Typically, 5g/L of sugar gives a touch of sweetness with up to 25g/L resulting in a sweet cider. An alternative is to add a non-fermentable sweetener, however some find the taste unsatisfactory or suffer gastric effects.
Also, carbonation enhances “mouthfeel”, typically 2.0 – 3.0 volumes of CO2 about the same as beer or soft-drink.
Malic acid is the dominant acid in apple juice. The ideal acid level for cider is 5g/L to 7g/L. This gives the cider its “bite” but juice often has low levels (3g/L) so high acid apple juice or even malic acid needs to be added to get a balanced cider.
As with acid, many apples are low in tannin so high tannin juice or exogenous tannin (powder, oak chips, black tea, etc) can be added to improve the flavor.
The other element to add is time. Since cider is a form of fruit wine, as it matures there is often a difference between one week, one month, six months, twelve months’ worth of maturing.
I suggest you use the search function at the top of the forum to find lots of information about these approaches.
It is likely that others will reply with their favorite methods of improving cider, like adding apple juice concentrate, other fruits, etc, etc.
I hope this helps.
Cheers!