"We want to double that this year," said Miss Aitken.
She said there is usually a last minute rush for events like this which she hopes will bump up numbers.
Miss Aitken said the festival was originally intended to be a "little festival".
"I was thinking four or five breweries in the town hall."
She asked a few breweries around Wairarapa whether they would come on board and from there it just "kept growing".
"The word spread, now basically every brewery in Wellington is at the festival."
The idea for the festival was floated about over a drink with friends, said Miss Aitken, and it came at a timely point in her life when she was working as a Government consultant.
"I needed a break from writing."
Miss Aitken said while Martinborough is known for its wine, it's a popular weekend getaway spot - part of the reason why the festival is held there.
"Martinborough is more than just wine, we've got olive oil, we've got a brewery."
There is also a growing craft beer industry and demand for good beer, even from wine makers.
"Some wine makers quite like a beer," she said.
At the brew day, there will be seminars, pub quizzes and live music, and of course a variety of beers available.
"There is a live homebrew to start the day in the seminar tent," said Miss Aitken.
"All the brewers are happy to have a yarn."
There will be beers from Martinborough Brewery, Regent 58 and Peak Brewery (Wairarapa); Panhead Custom Ales, Baylands Brewery, ParrotDog, Fork and Brewer, Blackdog Brew Co, Yeastie Boys, Funk Estate, Kereru Brewery and Garage Project, (Wellington) and Tuatara, Northend (Kapiti).
There will also be food from Wakelin House, Fork and Brewer, House of Dumplings, Hop Garden, Scotty's meats and Le Canard.
As well as beer, there are cocktails and non-alcoholic drinks from local producers.
A new Wellington-based vodka brand, Pimps Spirit, will be launched and cocktails will be made from WildFern liqueurs.
This year there are also tasting packages on offer which are expected to sell out in the next couple of weeks, said Miss Aitken.
The brew day is on 8 March, visit www.brewday.co.nz for more information and to buy tickets.