Stabilization, Degassing and Clearing/Fining
Depending on if you have put your wine through secondary fermentation (malolactic fermentation) and it has stopped producing the small pin hole bubbles, or if you are proceding directly from the completion of primary fermentation, it is now time to stabilize, degass and clear (fine) your wine.
Let's start with Stabilization.
Stabilization
This is a very important step, as you absolutely do not want your wine re-fermenting past this stage. (That is, unless you want popped wine bottles all over the place). To stabilize your wine you are going to need a combination of Potassium Sorbate (or if you can get your hands on it - Potassium Benzoate) and either Campden tablets or Potassium Metabisulphate. The combination of these two chemicals will help to create an environment in your wine that yeast do not like and should render them harmless from causing refermentation. Let's first discuss what each of them do during this process.
Potassium Sorbate:
Potassium sorbate is used to inhibit molds and yeasts in many foods, such as cheese, wine, yogurt, dried meats, apple cider and baked goods. It can also be found in the ingredients list of many dried fruit products. Also known affectionately as "wine stabilizer", potassium sorbate produces sorbic acid when added to wine. It serves two purposes. When active fermentation has ceased and the wine is racked for the final time after clearing, potassium sorbate will render any surviving yeast incapable of multiplying. Yeast living at that moment can continue fermenting any residual sugar into CO2 and alcohol, but when they die no new yeast will be present to cause future fermentation. When a wine is sweetened before bottling, potassium sorbate is used to prevent refermentation when used in conjunction with potassium metabisulfite. It is primarily used with sweet wines, sparkling wines, and some hard ciders but may be added to table wines which exhibit difficulty in maintaining clarity after fining. One of the negative effects Potassium sorbate can have on wine is that if too much of it is added it can give the wine a bubblegum or beewax aroma which some people may find offensive.
Potassium Benzoate:
Like Potassium Sorbate, Potassium Benzoate is yet another chemical that will stop yeast from refermenting wine. Potassium benzoate (E212), the potassium salt of benzoic acid, is a food preservative that inhibits the growth of mold, yeast and some bacteria. It works best in low-pH products, below 4.5, where it exists as benzoic acid. The main difference between these two chemicals is that Potassium Benzoate is not known to produce the bubblegum/bees wax aromas that Potassium Sorbate is known for. Therefore, it is recommended that if this chemical is available to the home wine maker, it should be the preferred choice. Sourcing Potassium Benzoate suppliers can be a very tricky endeavour though and generally speaking it can cost anywhere from 5-10 times the price of Potassium Sorbate.
For both these said chemicals you will need .44 grams per litre to properly stabilize your wine.
Potassium Metabisulphite (K-Meta):
Potassium metabisulfite (K-meta) is a common wine or must additive, that forms sulfur dioxide gas (SO2). This gas both prevents most wild microorganisms from growing, and it acts as a potent antioxidant, protecting both the color, and delicate flavors of wine. Generally speaking you should not allow the amount of Free Sulfer Dioxide to drop below 40 ppm (parts per million). When stabilizing your wine it is recommended to use at a minimum of 50 ppm. Remember not to over use this chemical as it can contribute to a sharp, unpleasant sulfer smell and taste (Do not exceed 80ppm). The amount of free sulfer dioxide you will need in your wine is dependent upon the pH of your wine. Before primary fermentation you should use a small amount of K-Meta to keep the 'wild yeasts' in check and allow the engineered yeast you have chosen to do their job. It is recommended that prior to primary fermentation that you put in enough K-meta to achieve a free s02 level of 25ppm. During fermentation some free s02 will be created naturally. If you put in too much K-Meta and exceed 25ppm you may be hindering your own yeast from fermenting the wine and you may end up with a stuck fermentation. To determine the how much Potassium Metabisulphite you will need to add to achieve your desired level of free s02 (sulfer dioxide) you can use the sulphite calculator
Once you have added in the required Potassium Sorbate/Benzoate and Potassium Metabisulphite you can move on to degassing and clearing/fining your wine.
Please note that when you add in both the Potassium Sorbate/Benzoate and Potassium Metabisulphite it may result in the release of suspended C02 in your wine causing your wine to foam. Before adding these two chemicals it is advised that you put the carboy of wine somewhere that it will be ok if it does over flow a little bit. The same warning is givien for when you degas your wine.
Degassing and Clearing
These two next processes are put together because you will for the most part be doing them in sync. Firstly, once you have properly stabilized your wine it is now time to add the clearing agent. The brand you use will depend on what is available at your local wine making store. They come in packets that are usually made for 6 gallon (23 litre) batches.
Here are a couple choices to choose from:
Bentonite
Probably the choice of most winemakers, as it is easy to prepare and easy to use. It is prepared as a 5% slurry by mixing 50 grams of bentonite powder into one litre of hot water. It is important that the resultant mixture be very smooth and free of lumps, so it is recommended that the slurry be prepared in a blender. Let the slurry stand for at least twenty-four hours and stirred well prior to use. The standard dosage is 4.5 cc per litre. Over-fining with bentonite may strip wine flavour, reduce body and colour in young red wines and impart an earthy flavour. (1)
Gelatine
Used for two basic reasons: clarification and reduction of overly astringent wines. It is also used prior to fermentation in order to reduce astringency and improve clarity. Gelatine is usually used with kieselsol, the two opposing electrical charges attracting most of the suspended solids. Gelatine is prepared from a powder form much finer than that used for cooking (look for 100 bloom, the measure of gelatine particles) at the rate of between 0.02 to 0.04 grams per litre. It may be necessary to use more than the recommended amount if the object is to reduce astringency. It is best to do lab tests before treating the entire batch, particularly if the intent is to reduce astringency. To prepare gelatine, mix the desired quantity in a small amount of very hot water and stir until it is dissolved. Once it has been dissolved, stir it into the wine. Liquid gelatine is available from R.J. Spagnols with a recommended addition rate of 0.66 cc per liter of wine. As a standard mixture, it works well enough with kieselsol for clarification, but if astringency reduction is desired, it is best to experiment with gelatine powder. Also, unless it comes in less than one litre containers or it is not used up in reasonable time, it can deteriorate, as it is an animal protein (1)
Egg White or albumen
A common fining agent for red wines because it reduces the harsher tannins. Some winemakers claim that it imparts a silkiness to the wine. Egg whites are used at the rate of 3 to 4 per twenty-five gallon barrel. Since egg white contains both albumens (soluble in water) and globulin (insoluble), a bit of salt is necessary. Whip the whites into the water and salt until a smooth mixture is attained without foam, which will float on the surface of the wine and be ineffective. (1)
Kieselsol
The commercial name for liquid silicon dioxide and is readily available from R.J. Spagnols. It is used to reduce bitter components from white wines, and used with gelatine is a very effective clarifying agent. While the directions on the label recommend 2.2 cc per litre, addition at the rate of 1.4 cc per litre seems to be effective. (1)
In the strictest sense, carbon and PVPP are not fining agents in that they are not used for clarifying. Rather, they are used to remove or reduce oxidative odours and to reduce browning in white wines and reduce the "pinking" effects of some grape varieties. (1)
Carbon (activated charcoal)
Used to remove colour - decolorizing carbon, and to remove off-odours such as oxidation - deodorizing carbon, and is usually used in conjunction with PVPP as oxidized white wines generally show a brown tinge. Use at the rate of 0.025 to 0.6 grams per litre. It is best to make lab tests before adding to the entire batch, as too much carbon will strip the wine of both flavour and colour. Since carbon is a very fine powder, it may be desirable to use bentonite also in order to compact the sediment. (1)
PVPP
Removes the brown effect from oxidized white wine and is used to prevent the pink colour from some grapes. If used to remove the brown colour, it should be used in conjunction with carbon. Use at the rates between 0.12 to 0.72 grams per litre. As it is also a very fine powder, adding bentonite will compact the sediment. (1)
Once you have added your clearing agent, you can now begin the degassing phase. Using your long sanitized spoon, begin vigorously stirring your wine. The first time you do this you may get a lot of foam pouring out from the top of your carboy. Basically what you are accomplishing now is releasing all of the fixed C02 that was saturated into your wine during fermentation. This step is important because it turns your wine from being semi-sparkling into still wine. You should stir vigorously for 3 minutes, 6 times over the course of the next 24 hours. Make sure to keep track of how many times you have stirred. Once you have completed your 6th and final stirring, you can top up your wine, refit the bung and air lock and proceed to the next phase.
Note: This step is made much easier and will take much less time (4-6 mins) if you have a stirring rod. A stirring rod can be attached to a power drill. Refer to instructions on stirring rod package for more details.
1. Bill Collings, January 18, 2002 (http://www.bcawa.ca/winemaking/fining.htm)