Here is an in depth article about the presses that wineries can use
There are 3 main types of presses that wineries use.
- Screw press with incline drainer,
- Bag or bladder press and
- Basket press
Each has advantages and disadvantages. Simall Wines use a basket press because we believe it gives us the most opportunity to produce the best quality wine.
Screw press with incline drainer
This press is common in large wineries because it allows for continuous operation and has the highest level of extraction. It will extract about 820L per ton of grapes.
Grapes enter into the bottom of the incline drainer. The grapes are taken up into the screw press by an orger. As the grapes move up the free run juice is separated by screens and comes out of the bottom of the drainer. This juice is pumped into a separate tank and is used for the more premium bottled wine.
Once the grapes are in the screw press, they are pressed against a metal door by an orger to squeeze out the juice. This portion of the juice is called the pressings and often needs to be fined (more about fining in the coming weeks). It is used for wines that retail for less than $10 and cask wine. The pressed grape skins are called the cake. It is amazing how dry the cake is after the screw press!
Bag or bladder press
This press is very common because it is a good compromise between quality and juice yield. It will typically yield approximately 760L/ton.
Grapes can enter the press either from the top through a door or through the side by a pump and hose. The press can turn which helps the extraction of the free run juice.
Inside the press is a bag to one side and screens on the other side. The bladder inflates and deflates which squashes the grapes against the screens. The screens allow the juice to exit the press. This press is computer controlled. Once it is full the computerised cycle will inflate the bag to gradually increasing pressures from 0.2 bar to 4 bar. It will hold the various pressures for 4-10mins (depending on the winemakers settings) then deflate. The press spins a couple of time and then the bag inflates to the next pressure. A typical press cycle is
|Pressure||Time the pressure is held before deflating and spinning|
|0.2 bar||10 mins|
|0.4 bar||10 mins|
|0.6 bar||10 mins|
|0.85 bar||6 mins|
|1.2 bar||6 mins|
|2.0 bar||6 mins|
|4.0 bar||6 mins|
The press spinning helps the juice to drain. It takes about 3 hrs to fill the press, press the grapes and empty it. Once the press is full, processing stops which is a disadvantage.
The juice extracted from a bag/bladder press above 0.4 bar pressure is keep separate, lightly fined and added back to the free run juice.
The basket press is the most gentle press. It extracts the highest quality juice which often does not need fining. However its juice yield is typically low and it is a very manual process. The juice yield is usually around 650L/ton. Simall Wines uses a basket press because we believe it gives us the most opportunity to produce the best quality wine.
The stainless steel basket and juice tray have to be removed from the press by a forklift and filled with crushed grapes. The basket and tray are then put back in the press and the the hydraulic rams are brought down onto the crushed grapes. The computer control is started and the juice is pumped out of the juice tray as the press runs. The computer controls the pressure in a similar way to the bag press. The grapes cannot just be squashed straight down because they squirt out the top of the basket and hit the roof!
The total press time is about 45mins. The cage then needs to be removed from the cake. The cake and juice tray is removed from the press. The cake is shovelled off the tray and fed to the cows (yep the cows love vintage!). The basket is then put back on the juice tray and it is refilled.