I purchased some citric acid from Akins last night as I'm lucky enough to have a store relatively near me:
Citric Acid 100% Pure - Now Foods. I couldn't find the canning citric acid, of course this is absolutely the wrong time of year to try to find canning supplies. I wanted to get pure citric acid to avoid lemon flavor, and also the sugar in lemon juice. I mixed the citric acid with distilled water, approximately 20% solution which is probably WAY stronger than needed. Super sour stuff and I'm wondering what the PH is... I'm too lazy to calculate this right now but it's probably more acidic than any lemon juice is ever going to be.
I've mixed one drop of the citric acid solution into Capella's gingerbread 10% flavoring and I'm not tasting any adverse effects from it. The flavor is "brighter" than I remember, there is a slight aftertaste. I think I'm going to cut the citric acid solution to half strength. I don't feel that this particular flavor would be adversely affected by lemon undertones though.
I'm mainly doing this to test the preservative effects of adding acid to the mix. I'm wanting to run an experiment with 3 or more solutions containing acids to compare side by side the outcome. I'm going to do this with TPA "toasted marshmallow" flavor since this one has been problematic for me. This flavor turns dark brown after several days to a week, gets acrid, becomes very harsh, and the last stage becomes a waxy flavor that in no way resembles the original. I get the same problem with Capella's raspberry, vanilla custard (diacetyl warning!), and several other flavors that I like. I have some vanilla custard I've left sitting as a pseudo-experiment, I think it has turned to tar. I don't know how others can't be having this happening?
I'll post photographic results when I get that far, probably in a week or two.
*Edit
tl;dr - experimenting with the long term storage effects of adding acid.