A real-world lesson in testing your must and changing your plan when the grapes demand it

It was a perfect day for crushing grapes.

We were preparing 660 pounds of Sangiovese and Merlot grown nearby in Castelnuovo di Farfa, in Italy’s Sabina region. That is me on the left looking perfectly at ease. The sun was shining, the setting was beautiful, and the grapes tasted wonderful. We were surrounded by ripe fruit, old stone buildings, and everything you might imagine when picturing a day of making wine in the Italian countryside.

Look at this scene. Look at this setting. Look at these grapes. Even the cat lounging in the background was relaxed. What could possibly go wrong?

As the day unfolded, we crushed the grapes and meticulously removed the remaining stems by hand. Hours later, our palms were stained purple. We were tired, the tanks were finally filled, and I was ready to take my hydrometer reading.

That was when the screeching strings from Psycho started playing in my head.

The hydrometer rose past 1.110 and kept going.

That was where the scale ended.

Curiously, I had recently written another article called “How to Make Better Wine From Fresh Grapes.” Its central argument was simple: you should not decide what kind of wine you are going to make until you test the grapes in front of you.

Apparently, the grapes wanted to make sure I practiced what I preached.

When the Hydrometer Runs Out of Numbers

I have been making wine for many years, but I had never encountered a reading this high.

The hot, dry summer was probably part of the explanation. I had noticed that some of the grapes were slightly dehydrated. As berries lose water, the sugar remaining in their juice becomes more concentrated. If enough dehydrated fruit was present throughout the harvest, it could have raised the sugar concentration of the entire must considerably.

Extreme heat does not always mean that grapes produce more sugar. Severe heat can interfere with photosynthesis and ripening. In this case, however, the visible dehydration suggested that water loss had concentrated the sugar already in the berries. I cannot prove that the weather was solely responsible, but it was a likely contributor.

Either way, I could not determine the exact starting gravity because my hydrometer apparently had not anticipated grapes with quite this much ambition. Based on what I could observe, the must may have contained enough sugar to produce a wine approaching 15.5% or even 16% alcohol.

Even the cultured yeast I had selected was not rated to reliably ferment a wine that strong.

I felt more than a few pangs of panic. I needed to solve the problem, and I needed to pivot quickly. Six hundred and sixty pounds of grapes were already crushed and waiting for me. This was not a small experimental batch that I could shrug off if things went badly.

So I did what winemakers must do when the grapes tell them something they were not expecting.

I went into research mode.

Imagining the Alternative

As I worked through the problem, I imagined what these grapes might have become in the hands of someone who never tested them.

Crush the grapes. Let nature take its course. Assume they will become wine because that is what grapes are supposed to do.

In all likelihood, it would have been a mess.

At that sugar level, the odds of a spontaneous fermentation finishing cleanly and completely were extraordinarily low. Native fermentation begins with an unpredictable population of yeast strains and other microorganisms. For this must to finish dry, an unusually alcohol-tolerant strain would have needed to be present, outcompete everything else, take control of the fermentation, remain healthy, and continue working beyond the rated alcohol tolerance of the cultured yeast I had deliberately selected.

Could all of that have happened? Theoretically, yes. Realistically, it was a terrible bet.

I was not going to risk 660 pounds of grapes on it.

The far more likely result would have been a fermentation that started normally, slowed as the alcohol increased, and eventually stopped with considerable sugar remaining. The struggling yeast could have produced sulfur compounds and other unpleasant aromas and flavors. The residual sugar would then have left the wine vulnerable to unwanted microbial activity and volatile acidity.

If it eventually became drinkable at all, it probably would have been a flawed, semisweet table wine.

There is nothing wrong with semisweet wine when you intend to make one. Accidentally producing one because the yeast could not finish fermenting is another matter. That is not a stylistic decision. It is just an unfinished fermentation.

Changing the Plan

Once I saw the reading, I knew I needed to reduce the sugar concentration and give the yeast a realistic chance of finishing the wine.

My solution was acidified, or acidulated, water. This is a standard winemaking correction made with water and tartaric acid. The water reduces the sugar concentration, while the tartaric acid helps compensate for the acidity that ordinary water would dilute.

The correction should be based on the must’s actual sugar and acid measurements, not an arbitrary volume of water. I also wanted to keep the addition below about 10% of the total must volume. Mine was approximately 7%.

Afterward, I tested again and confirmed that the specific gravity had fallen below 1.110. The wine will still be substantial, but I now know that I am asking the yeast to complete a fermentation it has a reasonable chance of surviving.

This was not an attempt to force the grapes into the wine I had originally imagined. It was a response to what the grapes actually gave me.

Letting the grapes lead does not mean refusing to intervene. It means measuring what you have, understanding what those measurements mean, and making the appropriate intervention when the fruit demands one.

Mine clearly did.

Testing Is Only Useful If It Can Change Your Mind

Winemakers are routinely told to measure sugar, pH, and titratable acidity before fermentation. Sometimes those tests are treated as formalities. Take the readings, write down the numbers, and continue with the plan you already made.

But testing is pointless if no result can persuade you to change course.

Had I skipped this test, the grapes still would have looked healthy and tasted wonderful. Fermentation might have begun vigorously enough to convince me that everything was fine.

The trouble would have appeared later, after the rising alcohol began overwhelming the yeast while substantial sugar remained. By then, I would not have been making a controlled correction before fermentation. I would have been trying to rescue 660 pounds of grapes from a fermentation already in distress.

The smell might have announced the problem before anything else did. Stressed yeast can produce hydrogen sulfide, which smells like rotten eggs. If you have never encountered it, trust me, you do not want to.

That is why you test.

Measurements do not make wine for you. They tell you when the wine you planned to make may not be possible. They give you time to replace panic with research and prevent a difficult must from becoming a ruined one.

I told other winemakers to let the grapes lead. This year, mine made certain I was listening by sending my hydrometer off the scale, and my anxiety with it.