I have entered mad scientist mode. After fining with a combination of Kieselsol and Chitosan and cold stabilization in the garage for two weeks, the wine tastes too tart. The initial touch to the mouth is sharp, which I kind of like, but the aftertaste is like grapefruit juice. Yeccchh. It seems clear from the taste that high acidity is the culprit. To be sure, I went out and ordered an acid test kit and a fancy electronic pH meter.
The pH meter was pricey at $45. I calibrated the meter using 4.00 and 7.01 pH buffered solutions. All three carboys read a pH of 3.4. Pretty good for a white wine. Now for the real test. The test kit included sodium hydroxide and phenolphthalein with a test tube and syringe. To determine Total Acidity (TA), the wine is placed in the test tube with a few drops of phenolphthalein. Sodium hydroxide (NaOH) is added one drop at a time with the syringe until the wine turns pink. I performed the test twice. First time it took 4 cc of NaOH and the second time it took 3.9 cc to get to pink. To get TA, the multiplier is 1.6 for the Sulfuric scale and 0.25 for Tartaric.
Sulfuric is from 6.2 to 6.4
Tartaric is from 0.98 to 1.0
For white wine the TA should be no higher than 4.9 for Sulfuric and 0.75 for Tartaric.
Now the dilemma. Riesling, being from Germany, is a cold weather grape. It grows well in the Finger Lakes. Cold weather grapes tend to have higher acidity because of slight increase in rot on the vine (simplified explanation). The acidity is desirable because it provides the wine with a crisp taste. I need to get the TA down to a desirable level without changing the pH or screwing up the crisp taste.
My options are: (1) to add some calcium bicarbonate (chalk) and risk altering the taste dramatically (adding three months minimum before bottling) (2) add water (cheap, but makes cheap wine), (3) dilute with low acidity commercial wine (expensive, but effective), (4) add some other type of carbonate like potassium carbonate which some say should only be done before fermentation and we are too late for that.
I also need to sweeten the wine to taste. For that I will use a sucrose and potassium sorbate combination that is often referred to as "wine conditioner".
Before doing anything, I plan to consult with the vineyard who sold me the grapes.
In addition to getting the taste right, I want my wine to look pretty too. That means getting it crystal clear brilliant. I tried filtering one of the carboys using the Vinimat gravity filter. Awful. I should have known when I saw the filter had a "made in England" stamp. When is anything ever made in England these days? It took nearly an hour to filter one third of the 5 gallon carboy and I basically lost a whole bottle's worth of wine just getting the wine to flow. This presents a danger to the wine because exposure will oxidize and ruin the very color and taste that I am trying to achieve by filtering. So I gave up and racked the last 2/3 of the carboy using my siphon pump and tube.
I also managed to get the Titrets to work great for the first time. To my surprise, the free SO2 was quite low. Around 20-25 ppm. So I added 1/4 teaspoon potassium metabisulfate to each. That should put the SO2 at around the 60-65 ppm safe range for each.