Choosing when to bottle a wine is one of the most important, nerve-wracking, and satisfying decisions a winemaker will make for any one vintage. For the large winery, it is a financial obligation to bottle on schedule and to maintain brand consistency. For the micro-winery, knowing when and how to prepare a wine for eventual consumption can be much more intimate and satisfying.
The pre-conditioning of a wine is essential to how it develops in bottle, and how enjoyable it will be over the long term. What the winemaker should be focused on during the actual making of the wine is creating an extended arc of potability – an amount of time after the wine is bottled during which the wine tastes best.
The better a wine is made, the longer it is likely to be consumable. The best wines are wines that are both enjoyable soon after they have been bottled and when they are aged. Following are a few tips on how to avoid problems when bottling your own wine.
The Big Picture
First, it is important to have a big picture of the wine at hand. A few key items to look at: Know whether there is any residual sugar in the wine; know if the wine has completed malo-lactic conversion (ML); know the pH and free sulfur level.
Residual sugar, in particular, can be have a nasty effect on otherwise healthy wine. Because sugar is the primary mechanism of fermentation, it can actually begin to re-ferment under the right kind of situations. Bottles have been known to explode, corks can be pushed out. An entire vintage can be ruined.
A few ways to avoid residual sugar effecting a finished wine are 1) Using a strong cultivated yeast to ferment the grapes/juice/must to dryness (< 0.4%); 2) sterile filter the wine prior to bottling (< 0.8 micron filter); 3) maintain a higher level of free sulfur in the wine as it ages.
The strains of bacteria that convert malic acid to lactic acid in malo-lactic conversion (ML) are particularly sensitive to sulfur. Keeping even a moderate level of sulfur should keep a wine from re-initiating ML in bottle. That being said, the safest way to protect against any unexpected post-bottling funny business is to filter the wine.
A free sulfur level of around 20-30 parts per million (ppm) is best during aging. As the wine ages, oxygen begins to metabolize ethanol thus making it more volatile and unstable. If left unchecked, wine can very quickly become vinegar. A higher level of unbound, or free, sulfur slows this inevitable process.
At bottling, the free sulfur level should be a little higher. Sugar and aldehydes consume/absorb sulfur readily. Knowing just when to add sulfur and to what end can greatly enhance the finished product.
Assuming that the wine is healthy (i.e. no residual sugar, a pH of between 3.3 and 3.7, and 25-40 ppm free sulfur) and ready to bottle, there are still a few items we need to have in place.
A Bottling Checklist
What type of bottle should you use? Cork? Synthetic? Crown-cap? Where will it be stored when you are done?
In my opinion, for the garagiste, a Bordeaux-style cloudy green/brown bottle can be very easy to fill and stack. The heavier the bottle, the more sturdy the container (and they can be reused). For those who wish to be more accurate with their bottle to varietal pairing, there is a bottle for every wine. You just have to do a little shopping.
Machinery can make bottling easy, but it can also be costly. For the micro-winery, a few simple tools can make the job fun and inexpensive.
My suggestion is to envision the entire bottling process from start to finish. Then establish an assembly line that helps you to bottle all of the finished wine in a single event.
A simple checklist for bottling should include the 1) bottles; 2) inert gas (nitrogen is good); 3) A way to get the wine into the bottle – filling wands are good for small quantities, while multiple heads are better for larger bottlings; 4) the closure – preferably some sort of cork, real or synthetic, and a way to get the cork into the bottle; 5) cases or a bin in which to store the bottles of wine.
The wine should be kept in a cool place before, during, and after bottling. It should go from an inert container (barrel/tank) to bottle and be sealed as quickly as possible.
Step by Step
First step: Sparge the bottles with gas – one to two seconds per bottle at 5 psi should do nicely. This protects the wine from oxygen as it moves from your storage tank to the bottle
Nitrogen is a good gas for this procedure because it does not effect the wine in any negative way. Carbon Dioxide should not be used because it can be absorbed into the wine and cause carbonation. Argon is good but it can strip the aromas of a wine.
Next, move the wine into the bottle. There are simple techniques and machines that can do multiple bottles at a time, but a simple siphon tube with a spring-tip wand can make filling each bottle easy and relatively painless.
Note that when filling each bottle to leave enough room for the cork/crown cap AND an additional 20 millimeters of space between the wine and the closure. This allows for expansion should the wine become warm.
Now, seal the wine bottle. My preference would be to use a cork, whether real or synthetic. (One of the problems with screw-caps is the very small tolerance for an inexact fit, and the machinery needed to get the foil spun down onto the threads of the bottle is expensive. Crown caps can be an inexpensive yet accurate closure, but they are not as romantic as a cork closure. Nor do they permit the wine to breathe.)
The corking process can be as simple as pressing the cork into the bottle with a hand-corker. My advice is to find a bench-style corker that also has a vacuum mechanism. The vacuum offsets the pressure of the cork being pressed into the filled bottle and can evacuate any extra oxygen that may have entered the bottle after it was sparged.
Finally, store the bottles on their heads, with the corks down. This minimizes the possibility of the cork pushing out of the bottle. If you have multiple cases, stacking each case on top of another will greatly enhance the amount of pressure operating against that of the pressure on each cork inside the bottle. If you use a vacuum corker, the need for stacking the bottles on their heads is lessened, but can still prove to be beneficial.
Storage of your bottled wine should be in a cool, dark place … like a cellar.
Barring any unforeseen events, if the wine was healthy going into the bottle, it will likely be satisfying to drink for months or years to come.
Good luck, and happy bottling.