Stockpiling and fermenting rotten fruit is a common way to make alcohol in prisons.

Prisoners being treated for substance abuse issues have managed to brew and drink alcohol under their guard's noses.

A group of eight inmates at Rimutaka Prison in Upper Hutt were foud to be intoxicated earlier this month.

The prisoners were in the Drug Treatment Unit, a rehabilitation unit designed to reduce reoffending by teaching participants about their addictions.

Prison sources said the unit was more "laid back" than regular sections of the prison, which was likely how such a large amount of alcohol remained undetected.

Home brew, sometimes called "pruno" in jails, is commonplace and can be made using fruit, water, sugar and a plastic bag.

The Spring Hill riot in 2013 happened after 29 inmates got drunk and went on a 10-hour rampage at the Waikato Prison.

This lead to Corrections tightening up on how many extra pieces of fruit prisoners were allowed to buy, on top of the mandatory two pieces a day provided by the jailhouse kitchen.

But while fruit is the main source of home brewing behind bars it is not the only way. In 2011 a group of prisoners at Rolleston Prison in Christchurch became blindly drunk after they used hand sanitiser as a base to create an alcoholic concoction.

In a written statement, Rimutaka director Chris Burns said when staff became aware of the drunkenness the unit was locked down and home brew found in two of the cells.

The ringleader of the event was charged with misconduct and his security classification upgraded to maximum security.

All other prisoners were kicked out of the Drug Treatment Unit and returned to their previous units, he said.

"The ringleader of this incident was new to the unit and had not started his treatment for drug and alcohol abuse. The other prisoners were at various stages through their treatment.

"Unfortunately some prisoners will constantly try to find ways to challenge the system and attempt new ways to introduce contraband into prison so our staff must try to stay ahead of them. Our intelligence staff are constantly working to identify and mitigate risk areas in each prison's physical environment and to stay informed about new methods of concealment."

Corrections did not respond to questions about how such a large amount of fruit that would have been needed to make the home brew was able to be concealed.