I must confess my love for two types of wines: delectable icewine and refreshing sparkling wine, or bubbly, as it is more affectionately known. So when the wine industry in Niagara (Ontario), the world capital of icewine, first fused these two styles by creating sparkling icewine, I became doubly ecstatic. What better creation than to combine the delicious sweetness and oodles of tropical fruit flavors and aromas of icewine with the lively acidity of sparkling wine.
Icewine is an impeccably well-balanced sweet dessert wine produced from grapes naturally frozen on the vines. Most icewines are white and produced mainly from Vidal or Riesling, and exhibit aromas of peach, apricot and litchi, as well as nutty flavors in older icewines. Red icewines from such varieties as Cabernet Franc and Cabernet Sauvignon are now becoming popular too.
Making icewine, however, is a challenge and, coupled with very low yields, a half-bottle (375 mL) can set you back $40–60 or more. Add to that the cost and further challenge of making the wine sparkle and the price easily jumps to the $70–90 range.
The major challenge in making icewine is fermenting very sweet juice, as yeasts are inherently adverse to high sugar content (it causes excessive osmotic pressure on yeast cells) and will struggle to ferment. And then, yeasts are subjected to further stress when it is time to trap carbon dioxide (CO2) gas in the wine.
Fortunately for home winemakers, kit manufacturers now produce kits to make icewine-style wine, white or red. With a little ingenuity, you can use the concentrate as the raw material and using what is known as the Charmat or cuve close method to make the icewine sparkle. The choice of a concentrate is ideal since it was specifically designed to have a starting sugar density in an ideal range and it avoids the need of all the pre-filtrations required with freshly-pressed juice.
Process overview
Here, we will use an icewine-style concentrate from a kit, which will be fermented without adding any water, and we will make some slight changes to manufacturers’ instructions — all in the interest of ensuring a successful fermentation and to create the bubbles. The Brix (SG) of the concentrate should already be in the 35–37 (1.155–1.165) range, perhaps lower, but no higher; otherwise, you would be asking for trouble (stuck fermentation). And we will use the following typical values for sparkling icewine as an example to guide you.
The process involves fermenting the concentrate with a fermentation lock until such a point that we are ready to capture sufficient CO2 gas to get about 5 bars (75 psi) or more of pressure and the desired residual sugar (RS) content. To achieve this, the last 1.5% alc./vol. will be fermented in a closed, pressure-resistant tank or keg to keep the CO2 dissolved in the wine.
Here is how the calculations work
Assuming that the starting Brix (SG) of your icewine concentrate is 36 (1.160), or 418 g/L of sugar, this represents 19.2% potential alcohol. To get an actual alcohol content of 11.0%, the concentrate will need to ferment down to 16 (1.065), which represents a potential alcohol of approximately 8.2%, and leaving 170 g/L of RS.
Now the tricky part!
In our example, the fermenting icewine will need to be transferred to the keg when the Brix (SG) reaches approximately 18.8 (1.078), or 9.7% potential alcohol. Fermentation will stop on its own when the alcohol reaches approximately 11%; the Brix (SG) should be around 16.0 (1.065). Brix (SG) cannot be actively monitored for the final phase of fermentation once the wine is kegged as you should not open the lid while the wine is fermenting. For this purpose, you will need to monitor pressure inside the keg, and fermentation will be deemed to be over when pressure reaches its maximum and remains stable at that pressure.
In commercial sparkling icewine production, the wine is both filtered and bottled under pressure so as not to lose precious bubbles. In home winemaking, filtering under pressure is not possible, or at least not easily done, while bottling under pressure can be achieved using a counter-pressure bottler.
Preparation
Start with 3.2 gallons (12 L) of concentrate from a kit specifically designed for making icewine-style (still) wine. You can either start from a varietal such as Riesling or Vidal if you can find them, or you can use a blended concentrate. Make sure the concentrate is at room temperature; otherwise, a cooler temperature will likely inhibit an already-difficult fermentation.
The day before you start fermenting the concentrate, prepare a bentonite solution by dissolving approximately 12 grams of bentonite powder in 120 mL of water, and let stand overnight in a closed container. Shake the container every so often to help the bentonite dissolve. This solution will be added to the concentrate to ensure that the wine is protein stable. Note that this treatment, known as counterfining, is recommended to be done before yeast inoculation and fermentation to minimize bentonite and yeast interactions that could otherwise impact the difficult fermentation even further. Manufacturers may instruct to simply sprinkle the bentonite over the surface of the concentrate; however, this is not as effective as preparing a solution and may cause yeast to become inhibited.
Clean and sanitize a 5-gallon (19-L) carboy and pour in the concentrate. Do not rinse the bag of concentrate with water; this would change the starting volume and Brix, and alter the balance of the must. Stir the must thoroughly and withdraw a small sample to measure the starting Brix (SG) using your hydrometer and record the measurement.
If the Brix (SG) of your concentrate is lower than the desired starting level, add the required amount of sugar without exceeding the recommended range. Confirm the addition and starting Brix (SG) by taking another hydrometer measurement. Measure and record TA/pH, and adjust to the desired range by adding tartaric or malic acid, or a blend of both.
Add the bentonite solution to the concentrate, stir thoroughly, place a bung and fermentation lock on the carboy, let stand for a couple of days or until the bentonite has completely settled and the juice is clear, and then rack the wine into another carboy.
At least three hours ahead of inoculating the concentrate, you will need to prepare and acclimatize a yeast culture using a stepwise procedure. THIS IS VERY IMPORTANT!
Choose a strong fermenting yeast with low nutrient requirements specifically recommended for icewine production, such as Lalvin K1V-1116, and rehydrate two (2) 5-g packets in 100 mL of water at a temperature between 95–105° F (35–40° C) for 15 minutes. At the same time as when adding the yeast to the water, also add one teaspoon of natural yeast rehydration nutrients, such as GO-FERM®.
Then, dilute 50 mL of concentrate in an equal volume of water, both at room temperature, and add this 100 mL of diluted sample to the rehydrated yeast, hold for 60 minutes and stir the sample gently every 30 minutes. At this point, the sample should be at approximately one-quarter of the starting Brix of concentrate; in our example, that would be 9.0 °Brix (1.036 SG).
Now add 100 mL of concentrate to the starter culture, hold for 120 minutes and stir the sample gently every 30 minutes. At this point, the sample should be at approximately one-half of the starting Brix of concentrate, or 18.0 °Brix (1.074 SG) in our example.
Lastly, inoculate the concentrate with the acclimatized starter culture, add 1⁄2 tsp. of yeast nutrients (DAP) as a water solution and stir thoroughly. Place a bung and fermentation lock on the carboy and set the carboy in an area at room temperature, ideally between 20–25 °C (68–77 °F), to promote a favorable environment for the yeast. Fermentation should start very quickly and will be noticeably vigorous within a couple of hours.
For the final phase of fermentation where CO2 gas is to be trapped and remain dissolved in the wine to make it bubbly, you will need a keg — the type used for soft-drinks and beer — with a small modification. The keg should be rated for a minimum of 9 bars (130 psi) and it should hold the exact amount of wine with very little headspace to ensure that CO2 gas produced during keg fermentation remains dissolved in the wine. It is absolutely critical that wine almost completely fills the keg to the top (just under the IN port) with very little headspace; otherwise, not all CO2 gas produced will remain dissolved in the wine.
You will need to make a small modification to the keg. Simply bend the tube protruding from the OUT port to the bottom of the keg from inside the keg until it is positioned sufficiently high to clear sediment that will form. This is to allow transfer of wine from the keg to bottles when ready to bottle without drawing sediment from fermentation.
You will also need to mount a simple gauge on a port quick-connect with a short piece of reinforced PVC tube rated for 9 bars (130 psi), and then mount this on the IN port of the keg to monitor pressure inside the keg during the final phase of fermentation when trapping the CO2 gas.
Alcoholic fermentation
During alcoholic fermentation, measure and record the Brix (SG) every day, and stir the fermenting wine twice a day to get the yeast back into suspension.
Let the wine ferment until the Brix (SG) drops down to 18.8 (1.078) or as per your calculations. This can take as little as 4–5 days or as much as 2–3 weeks or more depending on your fermentation environment, namely temperature and use of yeast nutrients, as well as your starting Brix (SG) – the higher the sugar concentration, the slower the fermentation. It is also recommended to transfer the wine at a slightly higher Brix (SG) to ensure that sufficient gas is produced from fermentation to give wine enough bubbles. Therefore, in our example, the wine can be transferred when the Brix (SG) reaches approximately 20.0 (1.083) – it will be easy to release some pressure if it gets too high, whereas it will be very difficult to get
gas back in.
When the wine has reached the Brix (SG) point to start trapping CO2, you are ready to transfer it from the carboy to the keg. First, stir the wine thoroughly to get the nutrient-rich sediment back
into suspension.
Clean and sanitize the keg, and then transfer the wine from the carboy to the keg, filling it to just under the IN port with a little headspace. Replace the lid on the keg making sure that it provides a perfect seal and that the relief valve is closed.
As wine continues to ferment, CO2 gas will remain dissolved in the wine. Read and record the pressure to monitor fermentation. Let the wine ferment until the pressure maxes out — typically around 4.5–5.5 bars (65–80 psi) — and remains at that level for at least two weeks. If pressure starts exceeding 6 bars (90 psi), slowly open the relief valve to release some pressure to keep it at or below that level, and repeat until fermentation stops. Then immediately transfer the keg to cold storage (the colder the temperature, the better, but do not freeze).
Leave the keg in cold storage for a minimum of four weeks to let the
sediment drop to the bottom to get a clear wine. The wine will not be fined or filtered and so it is advisable to be patient and let the natural sedimentation process take its course.
Bottling
Clean and sanitize 32 375-mL, pressure-resistant bottles specifically designed for sparkling wine.
To each bottle, you will need to add sulfite to achieve a free SO2 level of 45 mg/L and add potassium sorbate to stabilize the wine and protect it against renewed fermentation. Prepare a 10% sulfite solution and, using a 1-mL syringe, dispense 0.3 mL into each 375-mL bottle. Then dissolve 1⁄2 tsp of potassium sorbate in 32 mL of water and, using a 1-mL syringe, dispense 1.0 mL into each bottle.
Prepare and setup your counter-pressure bottler and proceed to bottle the sparkling icewine under pressure. Remember that the keg and wine must be chilled as much as possible. Do not shake or disturb the keg during the bottling operation to avoid getting sediment back into suspension. Secure each bottle with a cork or plastic stopper and wirehood. Enjoy
You can enjoy sparkling icewine as soon as it is bottled, although a 6-month aging period will add further aroma and flavor complexities.
As you pour sparkling icewine in a sparkling wine flute, bubbles will seem less intense and less persistent than other bubbly wines — that’s because sparkling icewine is very sweet and has a fairly thick consistency. However, as you drink the wine, you should definitely feel the intensity and persistence in the mouth, assuming that you were able to generate and trap sufficient CO2 in the wine.
Daniel Pambianchi is General Manager of Maleta Estate Winery and author of “Techniques in Home Winemaking” (Véhicule Press, 2008). He is a frequent contributor to WineMaker.
