•Pre-fermentative juice substitution was performed for Cabernet Sauvignon and Shiraz.•Volatile and non-volatile compounds were analysed and sensory attributes were rated.•Shiraz colour and phenolic profiles were negatively impacted by juice substitution.•Sensory profiles of the wines differed depending on the substitution treatment.•An earlier harvest date could still be preferable for managing wine alcohol levels. Pre-fermentative juice substitution with water or early harvest wine has the potential to produce lower alcohol wines without critically modifying colour or tannin properties and only marginally changing volatile and sensory profiles. Whether this approach is suited to producing lower alcohol wines in the absence of excessive grape ripeness remained to be determined. The current study extends on pre-fermentative approaches to alcohol management under milder grape ripening conditions and builds on an existing study with McLaren Vale Cabernet Sauvignon fruit, allowing for a direct comparison under two distinct vintage conditions. Given its importance to Australia, Shiraz was also included and underwent the same consecutive harvest and juice substitution treatments. Cultivar-dependent implications on wine chemical properties were apparent and declines in wine colour and tannin were particularly evident in Shiraz wines, although impacts on overall wine quality and sensory parameters were minor when adjusting musts within the limit of 13.5 °Baumé.