Testing for Dryness, Empty Airlock: Wine Wizard

Testing troubles

Q: I’ve been frustrated with the use of Clinitest tablets for measuring the end point or final dryness in my homemade wine and have been wondering and reading about the use of electronic blood glucose meters that diabetics use. There have been several discussions in various forums and some scholarly work from UC-Davis back in 1998. It appears that while they may not be a total solution, there may be some use when the brix is at 0 degrees. Have you heard of folks using these devices for wine measurements and what are your thoughts on using electronic blood glucose meters?
— Dan Macone • California, Maryland

A: I share your frustration with the Clinitest tablet method for measuring residual sugar in wines, which is why I don’t use it anymore if I really need to get an accurate number. Between the mess (I hate cleaning the last little bit of colored crud out of the bottom of my test tube), the subjectivity (what color did it really turn?) and the relative inaccuracy (the color chart is really just not that accurate or duplicatable in my experience), I’ve moved on to other methods. Namely, those methods include using the simple hydrometer during fermentation until things get into the negative brixes and then over-nighting a sample to a wine lab for an enzymatic glucose assay. The latter is really your best bet for finding out if things are really and truly dry. Though it may sound extravagant to spend money on shipping (depending on how far away you live from a wine lab) and then slap down about $25.00 for a lab test, but I prefer to spend a little bit and get accuracy, a 24-hour turnaround time and numbers I have total confidence in.    

In my opinion, when it comes to residual sugar, winemakers always need to know their numbers and always need to be careful. That especially holds true for home winemakers, who often don’t filter their wines or have access to filters of an 0.45 micron pore size (small enough to exclude bacteria and yeast cells). Residual sugar is an issue because yeast and bacteria can metabolize glucose and/or fructose as an energy source, essentially chewing it up as food and spitting out carbon dioxide and other possibly stinky byproducts in the process.             

Additionally, the more food you give a microbial population the more likely it is that they will think it’s party time and will want to reproduce . . . resulting in even more microbes which can just keep perpetuating the problem (fizziness, cloudiness, smelliness) until their food runs out. This is why it’s best for you to use “good” bugs like Saccharomyces cerevisiae and malolactic bacteria to eat up all the food. These “well-behaved” microbes will ferment to dryness with a minimum of bad by-products. “Dry” is usually considered to be less than 0.20 % (0.20 g/100 mL or 2.0 g/L) residual sugar, which for most people is just at sensory threshold for sweetness taste-wise. Unfortunately though, some bugs will still find 0.20% to their liking so I tend to consider 0.10% or less as truly “dry” for my own comfort level.  

Empty airlock

Q: I am new to making homemade wine and I recently started my own batch of Pinot Grigio. A week in I realized that I forgot to put water in my airlock. The fermentation is still going on (I can see bubbles) and I now have water in the airlock. Tell me have I messed up the wine? Can I fix it if I have?
— Benjamin Adams • Brunswick, Maine

A: No worries, mate (as my Australian harvest interns used to say), you should be just fine. The water (I think water with a pinch of sulfur dioxide and citric acid is even better) in the fermentation lock is there to act as the final gas barrier between your fermenting wine and the air. Carbon dioxide gas from the fermentation exits, bubbling up through the water, while outside air can’t get in. Simple, brilliant and a bit of winemaking technology that’s been around for over a thousand years. Lucky for you, your fermentation was still going on when you did remember to put water in the airlock, so it’s pretty likely that not a whole heck of a lot of air had contact with your bubbling beverage. That is, your fermentation was actively off-gassing into the atmosphere, so the laws of physics dictate that while your Pinot Grigio’s carbon dioxide was going out, not a lot of air was coming in.    

However, had you neglected to have the airlock on the fermentation container when your fermentation was on its last legs or inactive, it’s likely you’d be hazarding some oxidative damage or some microbial undesirables making ingress. As a fermentation winds down to its last few degrees Brix, it behooves the prudent winemaker to start thinking about protecting the new wine from oxygen and outside microbial contact. At this stage, it doesn’t have that robust layer of carbon dioxide gas to protect it from air or oxygen-loving spoilage bacteria so it pays to be vigilant. Luckily, active fermentation (often the time during harvest when a winemaker is the most stretched for time and sleep) is a pretty forgiving time. This time, you skated by but I wager next time you won’t forget to put water in that fermentation lock!