THE secrets to the perfect cup of coffee have been uncovered by researchers at Southern Cross University.
Research associate Don Brushett said while most baristas have refined the process of making a great espresso, there were only four variables they could control.
Mr Brushett said the variables were the coarseness of the grind, temperature of the extraction, the extraction time and the vital coffee-to-water ratio.
"Tweaking these variables can mean the difference between a velvety smooth coffee and a bitter scalding mess," according to Mr Brushett's research, which was published on website The Conversation.
Mr Brushett found there was an inextricable link between the coarseness of the grind and the coffee extraction time.
"If you get a cup of coffee produced from a quality bean but it is too weak and insipid, the coffee may have been ground too coarsely."
"If the coffee is unacceptably bitter, perhaps the grind is too fine, with too-high levels of organic acids being extracted."
The research found the optimum grind, between fine and coarse, matched with an extraction time of around three minutes and 30 seconds, made the best cuppa.
Mr Brushett found coffee can be extracted hot or cold.
Cold brew coffee, where ground beans are put in cold water and allowed to brew for a day in the fridge, produces coffee lower in caffeine and much lower in bitterness than a coffee brewed using hot water.
If coffee is boiled, flavour and aroma is lost in the steam, producing a coffee that is weak in taste, yet high in caffeine and organic acids.
Time determines caffeine, bitterness and flavour levels, Mr Brushett found.
"Coffee extracted for a short time (less than 2 minutes) produces a brew high in caffeine but weak, or underdeveloped, in flavour, aroma and bitterness," he said.