Is there a trick to making coffee, particularly french press, taste less acidic?
Without any more specific information about the coffee you use and what recipe you use for the french press, we won't be able to give you a specific answer with a solution to your problem. However too acidic probably means that your coffee is underextracted. That means the water hasn't had enough time or wasn't hot enough to extract the flavor compounds you want out of the ground coffee.
There are a few variables that will influence extraction with french press. I already mentioned time and heat. A recipe that I have used with very good results is 6g coffee per 100ml of water, ground to the size of coarse salt with a steep time of 4min. At first you only add a little water (just off the boil), twice to three times the weight of coffee grounds and let sit for 1min. Then give it a stir (there will be grounds on the top forming a crust), add the rest of the water and wait until 4min. Plunge and immediately transfer your coffee to a preheated vessel, either your mugs or a jug. Important here is that you don't let the coffee sit as it will continue to extract and taste bitter after a few minutes.
This should give you an even, full bodied extraction. If you feel like it's still too acidic, you could vary the variables involved. If you grind slightly finer the extraction will be higher. Same thing if you increase the brew time a bit. I suggest you just play around and keep in mind that these variables are not independent of each other. Finer grind means faster extraction for example. With a basic understanding of how extraction works you should get the hang of it quickly.
If the coffee still tastes too acidic although you have tried all suggestions check if the roast is too light, since light roasts tend to have more acidity. Also the origin of your coffee is a factor, african coffees (there are many different regions and processing methods so this is a big generalization) tend to be more acidic, while sumatran coffees are considered the least acidic. Central and South American coffees will often have acidity levels in the middle range. It might also be sour because the coffee is stale (around 4 weeks after roasting for whole beans, much much much faster for preground) or it might just be shitty coffee.
This is a good little intro in the world of extraction (or rather which tastes are associated with different levels of extraction): Coffee Extraction and How to Taste It.
This is a very nice little graphic with explanations that helps identifying which extraction problem you have and how to solve it: The Coffee Compass.
Cheers and enjoy a nice cup of coffee.
Something to be aware of, you get acidity at the two ends of the extraction scale. Early in the extraction, the flavor is dominated by acids that contribute a "bright" acidity. This is similar to the acidity in non-citrus fruits. As the extraction progresses, other kinds of flavors get contributed, adding to that and balancing the flavor. If you don't extract long enough to get a lot of the other flavors, and use a higher ratio of coffee to water to make up for the thinner strength, those acidic flavors will be very noticeable. Using a lighter roast will also contribute to this.
If you over-extract, by using too fine a grind, water that's too hot (especially with an insulated carafe), and/or letting the extraction go too long, there are other kinds of acids that start contributing to the flavor in a noticeable way. These have a sour taste that isn't pleasant (not like the sour taste in lemons).
Being aware of the kind of acidity will tell you whether you're under- or over-extracting (if that's the cause rather than the coffee, itself).
A French press makes the brewing process less sensitive if you do it right. A brewing process like pour-over/drip or AeroPress relies on controlling all the brewing variables, including grinding the coffee to a relatively small, uniform particle size so all of the coffee brews at the same rate. You then control the extraction and stop it before the unpleasant flavors become noticeable.
French press relies on a different approach, and a coarse grind is important to that. It gives a rich, balanced taste by having the coffee contributing different levels of extraction at the same time.
As the portion of the coffee particles near the surface are starting to contribute some late-extraction flavors, the portion near the center is still early in its extraction. That keeps the over-all flavor in balance while allowing a bit of the more-highly extracted flavors to add to the flavor profile without overpowering it.
With a small, uniform particle size, you don't get more of the light-extraction flavors, so they tend to get covered up by later-extraction flavors. You also can't let the extraction go into over-extracted territory because with all of the coffee contributing those flavors, they become objectionable. If you're going to tightly control the flavor profile to produce a target taste, you need to tightly control all aspects.
The mix of extraction levels from a coarse grind is what allows French press to be much more forgiving of the precise brewing conditions. But you can still brew under- or over-extracted coffee with a French press if you stop the extraction much too early or much too late (an insulated carafe keeps the brew temperature higher, making it more sensitive to brewing too long).
So if you aren't getting balanced flavor from a French press, and you're using a grind finer than coarse, like you would with a different brewing style, go back to the basics of how French press is supposed to work and see if that fixes it. I know James Hoffmann uses a medium-coarse grind. He may like a more extracted flavor. Start with a coarse grind and then adjust to taste.
If you use a medium-coarse grind, try reducing the water temperature. That will reduce the extraction of some of the flavors associated with over-extraction, including the unpleasant sour flavors that you may first notice as an after-taste. With medium-coarse, I find that 195°F rather than 200-205°F water reduces that.
You will also probably find that with coarse-ground, you need a little higher ratio of coffee to water than you would with a finer grind. With a finer grind, you're extracting at a target level from all of the coffee. With a coarser grind, you're extracting to a greater degree from the coffee material near the surface of the particles, and stopping the extraction short on the material at the center of the particles. So you're extracting a little less of the good stuff in the coffee (the price of getting the broader flavor profile). I find I need about 17% more coarse-grind coffee for French press than medium-fine-grind for AeroPress to produce the same strength.