Hi Vasileia, this is an interesting question.
In short, instant coffee can be as acid as any other type of coffee. So, if you're looking for less acidic coffee, you need to consider other variables to decide.
Acidity is part of coffee's nature, and it's more or less present depending on:
* Coffee species: robusta has a lot more caffeine than arabica, and it’s more acidic too. Taste is more intense and provides more crema for espresso. When it comes to low acidity, it’s better to pick instant coffee made with 100% arabica beans. Bear in mind that arabica coffee beans are considerably pricier, so this kind of instant coffee will likely be more expensive.
* Roast: dark roasts tend to be more bitter than medium and light roasts but are less acidic. Green coffee has tons of natural acids that transform and eventually disappear during roasting. Dark roasts develop their kind of acids (quinic acid), which are responsible for bitterness, along with caffeine. In this regard, medium roasts can be the most ideal, and you’ll notice it in instant coffee in the color of the granulated product, which tends to have a lighter, reddish color instead of a dark brown one. In some cases, you’ll find brands that inform the roast of their instant coffee in their labels.
* Origin: high elevations are usually referred to as higher quality producers. However, these coffees can be more acidic when it comes to acidity. Farms in Colombia, Perú, Guatemala, Costa Rica, and Ethiopia, among others, are famous for their high altitude. Origins like Sumatra in Indonesia are well known for their low altitude arabica plantations. Brazil has so much diversity in coffee production that some estates grow coffee around 1200 masl. However, it’s unlikely to find single-origin instant coffee unless you go for specialty coffee which is considerably more expensive. Some companies offer specialty instant coffee with incredible results if you choose this venue.
* Brewing method: when it comes to instant coffee, there isn’t such a method, but using cold water reduces acidity considerably. If you’re looking for a low acidity drink, you can experiment by trying a cold brew with instant coffee. If you prefer to drink coffee hot, you can make a cold brew concentrate solving.
* Recipe: cream and sweeteners are sometimes the problems. Black coffee, however, needs to be of high quality to be palatable. Many instant coffee brands are undrinkable without sweeteners or cream. In this case, to have a most pleasant drink with low acidity, you can try almond milk, which tends to be easier to digest than dairy and other creamers.
As a final thought, if you’re looking for coffee with low acidity, you can explore all these variables to find what suits you best. I hope it helps!