Thomas Brogan, 46, "utterly lost control" of himself when he struck vulnerable Georgina Barnett, known as Doddy, repeatedly on the head and body as she pleaded with him to stop.
The victim, who had osteoporosis but managed to lead an independent life, died in hospital five days after the June 25 assault, having suffered 11 fractured ribs, extensive bruising and a deep cut to the back of her head.
Unemployed Brogan last month admitted murdering Mrs Barnett, a mother of one daughter, at her home in Ramsay Road, Kirkcaldy, Fife.
At the High Court in Edinburgh today, Lord Pentland jailed him for life and fixed the minimum punishment part of his sentence at 18 years.
Intoxicated Brogan, a frequent heavy drinker, had shared a litre bottle of vodka with a friend on the day of the fatal attack sparked by the "trivial problem", the court heard.
Passing sentence for the "horrific" murder, Lord Pentland told the killer: "Mrs Barnett was a friend of yours and sometimes permitted you to visit her. At no time had she done you any harm.
"She was a somewhat frail old lady, but she managed to live independently."
The judge said the pensioner would have been unable to defend herself.
"It is clear that you subjected Mrs Barnett to a vicious and sustained assault in the course of which you repeatedly struck her with considerable force," he said.
"In view of her age and the fact that she was frail and slightly built she would not have been in a position to defend herself against you, a much younger and stronger person.
"It seems clear that you utterly lost control of yourself and that this was caused by the fact that you had allowed yourself to become so heavily intoxicated by alcohol."
Mrs Barnett was a widow for around 30 years. She had lived in her flat for more than three decades and was well-known and liked in the local area.
The court previously heard that the motive for the attack was unknown but in the hours before the assault Brogan appeared to have been angry with a drinking associate "in connection with a mobile phone".
The fatal attack took place at about 8.30pm on June 25.
That evening, neighbours had heard thuds from Mrs Barnett's living room, then a loud crashing noise.
They heard the accused repeatedly shouting: "Don't f****** lie to me, I'll f****** kill you" and "stop taking the piss".
They rang police, believing Brogan was fighting with a man in the flat, but were shocked to hear Mrs Barnett's voice saying: "Tam, stop please."
When police arrived, they found Brogan at the flat with his hands covered in blood.
Mrs Barnett, on the floor in the corner of the living room, had severe facial injuries and was bleeding heavily from her head. Blood was spattered on a wall.
When she got to Victoria Hospital in Kirkcaldy, Mrs Barnett told staff that Brogan had beaten her up and that he had been angry.
She later told detectives he had come to her house drunk "looking for the boy next door" and voiced disbelief that he would do that to her "just because of that bloody sim card".
She died on June 30 after suffering multiple injuries, including the fractured ribs, a fractured sternum and damage to her brain.
Brogan, who has 10 previous convictions at summary level, offered a public apology via his lawyer at the last court hearing.
His QC, Mark Stewart, told the court today that the killer accepts full responsibility for his actions.
Lord Pentland said: "I accept that you have expressed remorse and regret for what you did to Mrs Barnett, though this will be of no comfort to her family who have suffered great anguish due to their loss."
Setting the minimum time Brogan must spend behind bars, the judge pointed to the many aggravating features of the crime - the unprovoked nature of the attack, the high level of violence involved, the fact that it was fuelled by gross alcohol consumption, the age and vulnerability of the victim and the fact that the attack took place in her own home.
The sentence was reduced to 18 years from a possible 22 years to reflect the early guilty plea.
Speaking outside court, Mrs Barnett's nephew Thomas Johnstone, 62, said Brogan had received a fair sentence.
He said: "I'm happy enough at the sentence. The judge was fair enough in his comments. It was what I was looking for, and the family.
"I might even take time to go up to where her ashes have been spread and just have a wee quiet word with her later on today and just say, 'he's got a just sentence'."
He said the family went through hell during the time when his aunt was in hospital, suffering from her injuries. Relatives stayed by her bedside 24 hours a day until she died.
Mr Johnstone described Brogan as a "drunken hooligan, an animal", adding: "Words couldn't describe the injuries, they are that horrific.
"There was no defence that he could offer. We've all had a drink, but words just cannot explain what he's actually done.
"It has been very traumatic for the whole family. We'll just have to live our lives and get on with it, I suppose.
"I'm glad to know that he (Brogan) won't be seeing the light of day until he's 60-odd years of age."
The nephew described Mrs Barnett as a lovely, friendly woman.
"In hindsight it was her own kindness that's brought this about, letting people into her house. She's paid for it with her life," he added.
Detective Inspector Gary Boyd, who led the investigation for Police Scotland, said: "Only Thomas Brogan knows why he carried out this unprovoked and violent attack on his helpless victim, who was a much loved member of the local community.
"His actions demonstrate how dangerous an individual he is and today's sentence means he will spend a significant period of time behind bars.
"No prison term, however, can undo the hurt Thomas Brogan has caused the family of Georgina Barnett and I can only hope that they can now move on from this ordeal and begin to put their lives back together."