Citrus e-liquid flavours are very popular in today’s market, these e-liquids often have sharp notes with an underlying sweetness, the likes of lemon, lime and orange feature heavily in citrus e-liquid flavours. While citrus e-liquid flavours are very popular, it can be difficult to get it right, which is why people often describe citrus e-liquid flavours as harsh.
Most citrus e-liquid flavours use oil in the chemical makeup of the flavourings, presumably because they are extracted from the seeds or peel of the actual fruit. Not to be confused with some oils that could cause lipid pneumonia when vaped, these are perfectly safe. They also use ethyl alcohol to stabilize the flavour and keep it homogenised and I think it is this that causes Citrus e-liquid flavours on the whole, to be considered harsh. Steeping should allow for the alcohol to evaporate and smooth out any harsh notes so it is always a good idea to steep something you find harsh. Chances are eventually it will come good.
The other thing worth considering is that the PH of a recipe plays a key role in how harsh you perceive it to be – we know this because of the rise in popularity of nicotine salts. It makes sense that if they are using fruit oils extracted from actual citrus fruits it will be high in citric acid, thus lowering the overall PH value of the recipe. A lower percent of the offending citrus flavour or an ingredient to counteract the Citric acid would reduce the effect on the recipe, but finding the ingredient to counteract it could be a laborious task of trial and error as I wouldn’t expect many flavour companies to publicise the PH values of their individual flavours. In any case its more likely to be that oil/alcohol is the cause the harshness.