Method
Made two G&Ts. Both in identical glasses, with half a slice of lemon & lime in each, same amount of ice, each with the same volume of gin (50ml, Beefeater). But made one using Fever Tree tonic and the other with Waitrose own-brand tonic (both straight from fridge).
a) Compared both drinks myself.
b) Invited housemates to compare drinks and try and identify which was which.
Results
Only 50% success rate among housemates at identifying tonic used. General consensus that there is a detectable difference: Fever Tree is slightly sweeter. However, difference is very small and might not be noticeable without direct 1:1 comparison. No strongly expressed preference for either.
Notes
1) I am aware that part (a) was not a blind test and that part (b) was not a double-blind test. A better experiment might involve marking the glasses in some way that would not be visible when drinking but could be used to identify them afterwards. Then the glasses could be randomly exchanged to allow for a double-blind test.
2) The test did not include other supermarkets' own-brand tonics, nor other branded drinks. This was because most of those contain sweeteners. I already know that I can detect those, even in relatively small quantities, so this would be redundant.
Conclusions
Given how very subtle the difference is, it is very hard to justify spending £2.98/l on Fever Tree when Waitrose own-brand tonic is only 53p/l.
(Fever Tree does have the advantage that I can get it from Tesco, 2 minutes walk away, rather than cycling all the way to Waitrose. Surprisingly, though, it is even more expensive if I get it there.)
For Science!
