Before you start going crazy with a fermentation restart protocol, are you sure that it is really stuck? The first thing that I would advise you to do is to taste and compare your wine with your stepdad’s. At 9%, and compared to 15%, you should notice sweetness on the palate.
If your wine tastes dry or similar to his, then it might be a measurement or instrumentation problem. I’d also suggest sending a sample to your nearest wine lab (I use ETS Labs based in St. Helena, California, and there are many others around the country) and get an alcohol measurement to make sure your 9% is a “real” number as well as to see what the residual sugar is, i.e. how far you’ll have to go if you do need to do a re-start. Unfortunately, human error and equipment variation can sometimes give us the wrong numbers.
Restarting a stuck fermentation is very difficult at this stage and takes a lot of time and some expense (more yeast, more nutrients, etc.) and somehow never quite makes the wine taste like it originally should have, (which is why the Wine Wiz always preaches “healthy fermentations first”). Similarly, I always make sure that the wine is really and truly stuck, by either running subsequent Brixes, “sugar pill” tests or sending samples to a lab if you can afford it, before attempting a restart. Sometimes a wine just gets cold and when the weather warms up the fermentation will complete itself. Other times, a fermentation just really slows down but will eventually finish. Unless the volatile acidity (VA) or other off-characters start to rear their ugly heads, it’s almost always better to let a fermentation complete itself naturally before making a huge fermentation restart attempt.
Likewise, I sometimes ask folks if they can’t live with a little residual sugar. If you’ve got 2-6 g/L (0.2-0.6%) residual sugar, and if you can sterile filter the wine (if you own a filter or can borrow or rent one), sometimes that extra sugar will just add a little body and mouthfeel, even if the wine isn’t textbook dry. However, if you have above 10 g/L, you’re really going to perceive the wine as sweet and it might be better to do as your stepfather suggests, and fortify the wine up above 17% by adding good quality brandy, perhaps adding additional sweetener, and turn the batch into an awesome Port-style wine.
I have a soft spot for Port-style beverages, having pioneered the “Bouteille Call” (yes, that’s what Randall Grahm decided to call it) Syrah and Raspberry sweet wine at Bonny Doon Vineyard back in the early 2000s. Lest you think these kinds of wine aren’t “serious” wines, let me submit that the higher alcohol and sugar generally make for longer aging and deeper complexity over time. Port-style wines are also perfect for so much more than just the dessert course. I love to use them in pan reductions for meat dishes, in creative cocktails (float a half-ounce over pink sparkling wine or use a teaspoon to pump up the cherry in your Manhattan), or as a perfect after dinner nut and cheese pairing. If you want to go sweet, just don’t drink your wine for dessert; make it a key part of the dish. Mix with plum or blueberry jam and reduce by 1⁄3 for a fabulous vanilla ice cream topper. Try a mixture of blackberry purée and sweet red wine in your ice cream freezer for a grown-up and very unique sorbet. As you can see, there are so many options for embracing a fortified red wine in your life and culinary repertoire.
If you just must restart this stuck fermentation, I suggest going on winemakermag.com and plugging “stuck fermentation” into the search box on the upper right hand corner. Many of us have weighed in on this topic over the years — I like James Henrie’s article from the Fall 1999 issue, available at www.winemakermag.com/story704.
Also, check out a nice wine industry reference at www.enartisvinquiry.com: Click on “Technical Information,” then “Winemaking,” then “Restart a Stuck or Sluggish Fermentation.” Their information is a very thorough step-by-step guide through what can be a long and involved process. Good luck!