Here is an update on my attempt to make a passito from Frontenac Gris…
After about 2 weeks of drying in the greenhouse, the grapes had lost about 50% of their moisture. I decided to press them at this point, not knowing how well our tiny little hydropress would do with raisins! I had close to 10 kg of grapes (ahem, raisins) that I pressed, and got about 2.5 liters of “juice” from them (the consistency was more like syrup). I think a commercial press that went through a long series of slowly increasing the pressure might have gotten a bit better yield, but I was happy with what I got. The resulting juice/syrup was a deep amber to brown color. There was a slight copper tinge to it. We’ll see what the color is like after fermentation.
Now on to the most spectacular result…
At just 50% dehydration, I didn’t know what to expect for sugar numbers (I think typical passito is dried a bit further). However, I think I didn’t need to dry them out quite as much! The extracted grapes had a sugar concentration of 55 °Brix! That’s INCREDIBLY sweet! That’s the equivalent of almost 700 g/L (70%) of sugar. Coca-cola contains about 111 g/L of sugar. Maple Syrup contains 800-900 g/L of sugar. So… you can imagine how sweet this really is! The good news is that the Total acidity came in at 15.5 g/L, so I’m hoping that this will help balance the finished wine.
The problem with a wine containing 70% sugar is that the osmotic pressure is too great for most yeast to undergo fermentation. They find it difficult to transport waste across their cell membrane, so they die. There is one wine that I know of with an equivalent sugar content to what we achieved with this Frontenac Gris: Tokaji Essencia. This is a legendary Hungarian wine made from the juice that drips from dried, botyritis-infected berries. So, essentially, the free-run from botryitised raisins (if that makes sense). It has been known to reach 85% sugar in some years, but normally ranges from 50-70%. The other interesting thing about Essencia is that it can take 6-8 YEARS to ferment, and only obtains up to about 6% alcohol.
So, since I didn’t want to wait years to see what the final wine will taste like, nor did I want a wine with only 6% alcohol, I decided to add back a little bit of water to my Frontenac Gris. I brought it down to a still very respectable 45 Brix.
I started fermentation using a modified pied de cuve method. I re-hydrated the yeast as one would normally do, but I used a larger quantity of water (I used 600 mL – the quantity I needed to dilute the wine to 45 brix). Then, I slowly added the syrupy goodness of the juice over a period of 24 hours. This allowed the yeast to slowly acclimate to their new (very harsh) environment, and ensured that my initial population of yeast was high. I used DV10 yeast because I know it’s pretty resistant (and it was on-hand). I would have preferred to use a yeast that is specifically made for ice wine/late harvest, but didn’t feel justified in ordering a whole package of yeast for this small quantity of wine. It seems to be fermenting nicely, regardless. I wonder how long it will take to finish… I’m excited to try it!