As an example, Coca-cola has cinnamon in it, which is almost impossible to taste when it's carbonated. It pops out when Coke goes flat.
Most sodas will have a citrus component. Japan has odd ones like Yuzu, so try to pick up some essential citrus oils that aren't normal in your home country and are plentiful there.
Then really, just put it onto stuff that you know the flavor of and taste/smell it to see if you can tell what's been added. Dip some white bread into it and see if anything comes out, etc. Don't be afraid to swirl it around in your mouth (like wine) or just breathe it in.
FYI, I was just in Japan and realized that their Sprite has a lot more lime than other countries, which I didn't really like. Normally Sprite is great in hot weather, but the lime just didn't work in the heat IMO.
Well that's because there wasn't enough gin.
If none of that is a possibility, try to find a certified sommelier, preferably a class where you can have a teacher and students taste test it. Their training involves learning to distinguish a bunch of aromatic compounds using an essential oil kit so they might be able to isolate some of the flavors.
If you really want to do it using just the stuff in your kitchen, you could order an aroma training kit and try it yourself. Otherwise, I’m afraid reverse engineering it yourself is really hard. There are over 2,600 flavoring food additives recognized by the EU, alone. The benefit of doing it with a trained sommelier is that they can help figure out substitutions even if they can’t identify the exact flavor.
She generally found it very difficult and laborious to get right.
> 果汁（ぶどう、レモン）、糖類（果糖、砂糖）、食塩、レモンエキス、シークワーサーエキス、うんしゅうみかんエキス、ゆずピール、ドライトマトエキス／香料、乳酸、塩化Ｋ、酸化防止剤（ビタミンＣ）
TL:
> Fruit juice(grape, lemon), sugars(fructose, sugar), table salt, lemon extract, C. depressa extract, C. unshiu extract, yuzu peel, dry tomato extract/flavoring, lactic acid, potassium chloride, antioxidant(vitamin C)
it's not always this detailed for Japanese beverages tbc - e.g. for that reportedly horrendous liquefied frisk[2]:
> GABA（国内製造）／炭酸、酸味料、香料、甘味料（アセスルファムＫ、スクラロース）
TL:
> GABA(domestic sourced)/carbonic acid, acidulant, flavoring, sweetener(acesulfame potassium, sucralose)
Usually only a few aromatics will make up the bulk of the flavor and they’re well known molecules, especially if they’re synthetic.
Most soda is sugar water with a few well known synthetic flavors added so it’s easy to identify. Secret recipes like Coca Cola are far more complex to make without easy synthetic alternatives. Any recipe that caramelizes sugar, for example, is hard to reverse engineer.
1. https://en.wikipedia.org/wiki/Gas_chromatography-olfactometr...
Why not just import it? Or is this for fun.
2. Look up basic proportions & recipes for canned sodas online, just to get an idea about how much to use
3. Start experimenting, varying the ratios of each ingredient in each batch
Then, of course, there’s the big change from the original Coke recipe vs what we have today with cocaine being replaced by caffeine.¹
⸻
1. I’m pretty sure that in no country does Coke still use cocaine.
How does this work legally? There is a (single) company that is licensed by the DEA to import coca, and they sell the non-psychoactive part to Coca-Cola. I think the psychoactive part goes toward DEA-approved research purposes, but I’m less sure about that.
Coca-Cola’s competitors do not receive or use coca through this process, only Coca-Cola.
I suspect the flavouring component is so diluted nowadays that its kept because it's a valuable sideline having that import license, and adds to the mystique a bit.