Could preparation method make coffee more acidic? This is more of a vague feeling than something I'm sure of, but from the many cups I've drunk, I have a feeling that when prepared in a french press, my coffee tastes a little more sour/acidic, compared to a turkish brew. Is this a documented phenomenon, or is it just me? 

Of course, assume the same coffee is used both times, which by the way is some home-ground (blade grinder) arabica.
This is a perfect follow up to the "What coffees are the least acidic?" question! 

As always, Lets answer it with some data! My company uses machine learning, data science, and sensory science to build flavor profiling and quality control tools for the craft beverage industry. 

TL;DR: Yes. Preparation has a significant affect on the flavor profile of coffee - including the level of acidity. 



Distribution of Acidity by Brewing Method



If I may present to you... the distribution of acidity in coffee by brewing method! 
Clearly and without surprise, Espresso (coffee extracted under pressure) is the most acidic preparation method, on average. French Press (full immersion brewing) is the least acidic, and V60 (a type of pour-over) has the widest range.

But is there something else going on here? 
What if there exists a conflating factor such as green processing, roast level, or growing environment? Some of these questions we're already answered in the link above, so lets focused on the remaining question - how does the origin of the coffee effect the perceived acidity of the coffee by brewing method? 



Acidity by Brewing Method Controlling for Continent of Origin



So is the effect of brewing method consistent? No. 
What we're seeing here is that each continent tends towards a different green processing technique, and thus a different optimal level of roast - all of which exert as much influence over the resulting level of acidity in the flavor profile of the coffee. 



Please just save me from exogenous variables

Oh... you should have just said so.... 



This is a conditional inference tree mapping the distribution of acidity scores to a series of categorical variables. 

Where:
C is Country 
P is Preparation 
G is Green Processing
and the bar plot shows the distribution of acidity


Country is clearly the most used variable in creating this tree, and interestingly, Green Processing is only used as a splitting rule when a country has a variety of green processing methods in common use. 



Please leave a comment if you'd like me to add a variable or further analysis to this answer!