A Masterton private school has defended its NCEA beer brewing science classes but community leaders are unimpressed.

Earlier this week Masterton deputy mayor and mayoral candidate Rod McKenzie said he had been "surprised" to learn students were brewing beer.

Today, Rathkeale College principal Neville Duckmanton said the home brew experiments had been carried out at the school for the past three years as part of Year 11 NCEA science course.

The experiments were conducted under strict conditions and "the tops never came off the bottles", Mr Duckmanton said.

The class of 15 and 16-year-olds did the experiment to illustrate the actions of living organisms.

Students worked under strict conditions and were not allowed to consume the product, he said.

Parents were allowed to pick up their student's beer making efforts if they wanted - otherwise it was thrown out.

But Wairarapa police head Inspector John Johnston said the school risked breaking the law if they allowed under-aged students to take alcohol home.

He said if police stopped a car driven by a minor carrying alcohol the offender could end up facing charges.

Mr Johnston said if the school wanted to experiment with fermentation they should consider making bread or ginger beer instead of alcohol.

Wairarapa-based New Zealand First MP Edwin Perry also opposed the experiment.

"There is plenty of time for young people to find out about booze without them learning about it in class," he said.