Great wines go through these steps. This is a detailed article about juice clarification, racking and a little on inoculation
Cold settling, racking and inoculation
We all want to enjoy gorgeous clear white wine. So, to deliver just that, winemakers must take steps to ensure their wines have every opportunity to develop to optimal quality and present beautifully in the bottle. So what are some of these steps? What are inoculation, racking and cold settling?
Once we have pressed white juice in the tank we need to get it cleaned up. During the pressing process, solids enter the juice. If we leave the solids in we would have a brown wine with plenty of funky, interesting characteristics. These characteristics are often undesirable and your may stop at the first glass (not good if you are a winemaker trying to sell wine). Sooo what we do is clarify the juice. As you would expect with such a critical step. I have options. They are:
- Floatation – A great continuous process that the big winemakers use. Nitrogen gas bubbles and gelatine are forced into the rack valve of the tank of juice. The gelatine helps the finer particles bind together and the fine nitrogen gas bubbles get under these particles and make them float to the top. The heavier particles bind together and sink. The clear juice is pumped out of the middle via the rack valve
- Centrifuge – juice flows over the top of perforated screens. These screens spin very fast. The juice falls through the perforations and the solids are flung to the sides of the machine and exit out the back. This is an expensive but continuous process used by big wineries
- RDV (rotating drum vacuum) (pictured above) – As the name suggests this is a drum (on its side) which rotates. on the outside of the drum are perforated screens. At the bottom of the drum is a bowl in which the drum turns in. A special filtration aid which is an inert fine powder is mixed in water and pumped into the bowl. As the drum rotates through the bowl, the vacuum causes the earth to stick to the outside of the bowl. This forms a cake around the drum. The dirty juice is then pumped into the bowl. The cleaned juice goes in through the cake and is pumped into a nearby tank. The solids remain on the outside of the cake and a blade cuts down the cake removing the solids and a small amount of the filter aid. This fresh section of the cake then goes into the bowl again and the process continues. RDV’s come is a range of sizes to suit various sized wineries. This is a messy process, commonly used on very dirty juice. It is also oxidises the juice which is not desirable
- Cold settling – All wineries have refrigeration to control the temperature of their ferments. So its easy to chill a tank of juice down to 5*C and hold it for a couple of days. This is cold settling. When you chill liquids they shrink a little. This helps to bring the solids closer together and they can bind and fall to the bottom. Chilling also slows down the energy in the juice which causes it to slowly mix itself. This also allows the solids to fall to the bottom. The clear juice is pumped from the top of the solids (process called racking) after a couple of days. It is a simple technique but it is energy intensive
Racking is the process of transferring the clear wine from off the solids to another. The process removes the wine from the “lees” (sediment) which primarily consists of dead yeast cells and particles (hydrogen sulphide compounds) that have fallen out of the wine. It is one of the steps to a brilliantly cleared wine because nobody likes a wine that has “stuff” at the bottom of it.
Racking is often be done up to 3 times:
- The first racking is usually done after fermentation, to protect wine from oxygen and to remove the wine from the “gross lees” (the sediment that falls out during the primary fermentation phase is called the “gross lees”, and this comprises about 80 percent of all of the sedimentation that will occur)
- For whites the second and final racking is performed once bentonite is added (for heat stabilisation) and the wine is chilled to -4*C and held for 7 days (cold stabilisation)
- For reds the second racking occurs after malo-latic fermentation (an important red stabilisation step that we will talk about in the future). Here the reds are usually racked into oak barrels.
- Red wine barrels are racked at the end of the year to clean up the wine and the barrels. It is necessary to rack the barrels at least once. It usually occurs at the end of the year because the winemaker is sick of tidying up and sweeping the floor
Inoculation allows the winemaker to control and manage the fermentation process of wine. This is done by selecting appropriate strains of yeast and bacteria so as to avoid the damaging and degrading impacts of inappropriate yeast and bacteria. This process is called –
- Yeast inoculation (using selected wine yeasts) and
- Bacterial inoculation (using selected lactic acid bacteria).
The latter is sometimes done after the alcoholic fermentation is complete but can be less effective than being done at the same time due to higher ethanol and reduced nutrients.
We will provide more info about inoculation that will surprise you. Stay tuned.