Tom is all over this blog right now, as it is absolutely time to talk wine all the time. In this piece, he gives the best tips on how to use an acid test kit and why you absolutely should use one.
The first time I made wine was in 1970 when our very old plum tree put out 12 bushels of ripe fruit. The previous year had been just as productive and everyone in the family was tired of canned plums and jam. Dad suggested I make wine, as I was the only one in the family who liked wine much. Figuring I might as well, I hit a store called WineArt Oregon on Broadway Blvd. Ann McCullum, the proprietor, insisted I get a hydrometer, air lock, carboy, yeast, acid blend and (importantly) an acid testing kit. She instructed me this kit was the best way to make sure the acidity in my wine was balanced and flavor enhancing.
I have used an acid test kit regularly since.
Why Acid Matters
Acidity is what gives wine the wonderful, refreshing flavor that makes us desire another glass. Without acid wine is flat and insipid. Furthermore, without acidity, wine will not keep as well. The acid level that is required is about 0.5% or higher. You will need at least 0.6% and above for a good crisp white wine and even more about 0.75% for sweetened dessert wines. All wines run a high risk of spoilage from bacterial contamination. Acidity is key to reducing contamination risk. Finally, if you are considering malolactic fermentation (“MLF”) for your wine, you will need to know the total acidity (“TA”) of your wine. Otherwise you might have too much acid for the malolactic cultures to survive, or so little acid that the cultures strip away the very acid you need.
How do we know just how high or low our wine’s acid is? By testing it. Remember, sugar masks acid very well so just tasting the fruit, juice, or must we have will fool us, because they will be at least 20% sugar.
Tips for Acid Testing
The acid test kit we carry is a color change titration type test. A titration test works roughly in the same way as the iconic “science fair project” volcano; it uses the reaction that ensues when combining acidic and alkaline ingredients, but for decision making instead of volcanic activity. So, when the sodium hydroxide (“NaOH”) from the kit is carefully added to wine, juice, or must in specified amounts a color change happens. When the color becomes either magenta or green (depending on wine type) we are done. The kit itself has very good instructions so I will not go into any further detail. However, there are a few tips for best practices I would like to pass along, based on my years of experience.
First, make sure your base is fresh for the season. Replace it with the like kind solution that came with the kit. (Our kits use a .01N NaOH solution.) If the solution is stale, your reading will be way off. The results aren’t pretty. I made a wine once that had over 1.5% acid when I thought it had 0.72% acid. I didn’t catch myself as I kept adding acid blend until I thought, “this just can’t be right” then it was too late. There was no way for me to save it. I had to dump it.
Even when you’ve got totally fresh reagents for your kit, bear in mind that it’s very easy to overshoot the color changes you’re looking for to get proper acidity. To test, you will be adding NaOH in 1 milliliter increments of reagent with a syringe. Swirl and mix in well each addition.
The color change for all white or very light colored musts (including red grape musts that haven’t been on the skins for any time yet) will be a pale pink shade.
For red-colored musts dilute the must with an equal amount of water. Then look for a change into a grayish purple tint as you add the NaOH. Once there you are done.
Here is an easy way to keep track of color changes in any must: when you make up your beaker of must for testing, make a duplicate in a similar sized glass. Then you can compare the musts as the color changes. By comparing them you will see the color change more accurately. Small tasting cups or 100 mL beakers are perfect. You need to be able to swirl them vigorously. When you’re pretty sure what the acid level is? Test it once more to be sure.
When you’re absolutely sure of your wine’s TA, it’s time to decide what acid adjustments you need to make and how you want to make them. For brevity’s sake, I am not going into much in the way of details in this piece. I will save that for another piece. What I will say is that many ways of adjusting TA in wine require a small scale that can do fractions of a gram. The adjustments will be all grams per liter, so you need accuracy (and possibly to brush up on metric units!) for the best possible results. An acid test kit is a valuable tool you should use.
It is impossible for your grapes to become the best possible wine they can become without you knowing their acid levels from day one. Ann McCullum did not steer me wrong 50 years ago, and now I strive to do the same for you. Use an acid test kit for all your future wines, whether they are grape wines, fruit wines, or honey wines.