The Importance of Topping Up
While oxygen is necessary in the early stages of fermentation it is also the mortal enemy of wine makers once a wine has gone still. Topping up your wine after fermentation is complete is the best way to minimize how much oxygen your wine is exposed to.
As our wines ferment we rack it from one container to another to get it off the lees. Each time we do this though we loose a bit of wine and increase the surface area of the wine we have left. This can leave us with too much head space at a time when our wine is most susceptible to oxygen exposure.
Topping up is the process of adding wine to your carboy, barrel, or tank to reduce the amount of head space (also known as ullage). This serves two very important purposes.
First, topping up reduces the amount of oxygen that gets trapped in your carboy or barrel after racking. Less oxygen means less oxidation.
The second thing it does is reduce the surface area of your wine. Carboys get very narrow up at the neck just filling up a barrel also reduces the surface area. This is important because the free surface of your wine is the interface through which oxygen can interact with the rest of your wine.
The smaller the free surface area of the wine is the more time it takes for your wine to become oxidized. This is especially important for small batches of wine.
It takes much longer to oxidize wine in a carboy because the free surface area is so much smaller than it would be if left in a primary fermentation bucket. Topping up your carboy ensures that the free surface area is kept to a minimum.
When to Top Up
During primary fermentation we need that head space so that we have room for the foam that will form. Also, because the yeast is producing carbon dioxide in such huge amounts there’s little chance of oxygen getting to our wine.
However, after primary fermentation carbon dioxide production decreases and is not enough to keep oxygen away from our wine. To protect our wine we attach airlocks or plugs but these are not fool proof and can let small amounts of oxygen in.
To combat this we need to be topping up after primary fermentation ends. Note that wine kits do not have you top up until later in the wine making process which is fine as long as you stick to the time line laid out in the kit instructions. Winexpert has actually removed the topping up step from their instructions.
Winemakers using oak barrels will experience much more evaporation because of the porous nature of oak. Also, because you can’t see how thick the lees is nor how deep your racking device is in the barrel a lot of wine gets left behind when racking. Thus topping up is critical when barrel aging wine.
What to Top Up With
Ideally when you make your wine you would have some in reserve to top up with. Wineries will often have a barrel or two to be used just for topping up. They take wine from these barrels to make sure their other barrels are kept full.
If you don’t have any wine set aside for this purpose the next best thing to top up with is another finished wine. Pick out a similar wine from the store and use that. It’s best to match flavor and sweetness as best you can but in the end it isn’t going to have a huge impact on your wine’s flavor because you’re not adding all that much.
Lastly there’s water. This used to be standard practice when making wine from kits. Manufacturers designed their kits to be topped up with water so that the final product would be at the appropriate concentration. However, Winexpert has recently changed their kit instructions and omitted the part about topping up with water.
Professional winemakers are actually limited on how much or even if they can add water to their wines legally. Generally speaking topping up with water just isn’t a good idea. Find a compatible wine and use that instead. You’ll have a better bottle of wine in the end if you do.