What is Racking?

The following is an excerpt from our April Wine of the Month Club.
Written by Mackenzie Brisbois.

Let’s get down and dirty with our lees!
Racking is when you move liquid from one container to another, taking only the clear liquid and leaving any deposit behind. It’s the reason my wines have any semblance of clarity (as I do not fine or filter).

What are these deposits?
    • Grape solids
    • Yeast and bacteria
    • Tartrate crystals
The settling of a tank or barrel depends on a few things such as:
    • Size and shape of a vessel,
    • Temperature gradient,
    • Size of the particle and stage of the wine.

  Generally, yeast settle quite nicely so it’s easy to see the separation and relatively easy to separate most yeast from the wine. When wine is racked it clarifies but it also picks up oxygen. The timing of racking and the actual technique are very important to limit the oxygen uptake. If a wine is racked during fermentation there is plenty of CO2 to protect the fermenting juice. When finished wines are racked there is very little protecting them and quite a bit of oxygen can be picked up if not careful.

Tall Tanks
The pressure from the hydrostatic head of liquid keeps carbon dioxide in solution in the depth of the tank. When a wine is racked and the pressure reduced, the gas comes out of solution as bubbles and can mix up the settled wine.

Temperature Gradients
If a tank is situated outside the winery there can be vertical stratification in temperature. Convection currents can occur if one side of the tank is warmed by the sun, mixing stuff up!

Size of Particle
Larger particles fall out of suspension quicker and easier than smaller particles. There can also be electric charges that affect the suspension of particles. Traditionally wines are fined with a substance that has an opposite electrical charge. I don’t use any fining agents so my wines could develop a haze during their time in the bottle. Fining is a different topic, but it is related because when a fining agent is added it is usually removed via racking and filtration.

Wine Stage
Wine that is fermenting creates CO2. The creation of CO2, in addition to the changes of fermentation, keeps particles suspended in liquid. This makes it very difficult to clarify a wine during fermentation: the biggest reason our Pet Nat’s foam over! A finished wine can also have a large amount of dissolved CO2. Pair this with a vertical tank and you can cause mixing while racking.