By: Thomas J. Payette, Winemaking Consultant
Often a winemaker is challenged with grapes, juice and wine that may have an imbalance in regard to the pH of a certain wine and that wines style. This can be a critical choice for the winemaker in terms of protecting the wine from spoilage. A wine with a higher pH is much more likely to develop spoilage bacteria/yeast problems. On the converse just simply adding acid to lower the pH may throw the delicate taste and balance of the wine off. Much finesse must be used at this time by the winemaker to make the proper decisions using both the wine lab and the wineglass.
Trials in the lab
The lab is the first place the winemaker should turn to experiment with small batches of wine. This will give nearly concrete evidence from the lab as well as tasting trials to determine the appropriate amount and kind of acid to add.
When?
The pH of a wine should be addressed as early on in the winemaking process as possible, especially if too high. Often this decision is predicted just before harvest from previously collected data (from field and grape samples) and made at harvest after chemistry confirmation on the crush pad. I’ll often start to make adjustments in the press pan of whites or in the must of crushed reds.
Why and Where?
The reason we do trials is to experiment with refinement and correction of a juice or wine. Always work in small quantities, in the lab, with a wine so one does not potentially create a larger problem, in the cellar. Trials can be tested and tasted to see what the results would be or will have been if the addition was made to the actual tank or vessel of juice/wine. This eliminates guesswork and unnecessarily “shooting from the hip” of which many winemakers can find themselves guilty of during critical times such as harvest.
Tools Needed
Scales that measure in grams preferably to a tenth of a gram.
4 3 – 100 milliliter graduated cylinder (plastic preferred)
4 1 – 50 milliliter graduated cylinder (plastic preferred)
4 1 – 10 milliliter pipette (Class A volumetric)
4 2 – 5 milliliter serological pipettes-one tenth mil markings (Plastic preferred)
4 Small glass beakers 250 milliliters plus or minus
4 Representative sample(s) of each wine to be worked with (800 milliliters)
4 Clean wineglasses
4 Watch glasses to cover each glass
4 Spit cup
4 Other testing equipment to answer questions at hand : pH meter, TA measuring, etc
4 Magnetic Stir plate with stir bars and retriever for the stir bars.
4 Sharpie™ pen or pencil for marking beakers.
4 95% ethanol to remove Sharpie™ pen marks off glassware.
How?
Start with something simple where results can be easily determined with the wineglass to give the confidence needed to build upon the procedure. An example of this may be a tartaric addition trial for pH lowering and/or palate modification. Let’s go over this process.
1. Start with an ample quantity of wine to work with in the lab – perhaps an 800-milliliter representative sample from a wine tank or vessel.
2. Accurately weigh 1.0 gram of tartaric acid and fully dissolve the acid in approximately 85 milliliters of the base wine with which you are working. Use the stir bar and plate for this process.
3. Once fully dissolved, place the full amount into a 100 milliliter graduated cylinder or as one becomes more experienced you may just make the solution in the 100 milliliter graduated cylinder directly.
4. Bring the amount of volume in the 100 milliliter graduated cylinder to the 100 milliliter mark with additional base wine. (One should be clear they have made a solution of 1.0-gram tartaric acid dissolved into 100 milliliters of wine.)
5. In a clean graduated cylinder, pipette 10 milliliters of the newly prepared acid stock solution into the cylinder. Bring to the complete 100 milliliters volume mark with the base wine. This represents a 1.0-gram per liter tartaric acid addition.
6. Pipette twenty milliliters from the stock acid solution made in step four into another graduated cylinder and bring to volume to the 100-milliliter mark. This represents the next addition level of 2.0 grams per liter tartaric addition.
7. Continue to add to the number of samples you care to do the trial on in standard logical increments.
8. Analysis the pH and titratable acidity, record and have available for the tasting below.
Set up the tasting trial
1. Pour about 70 milliliters or a quantity one desires to smell and taste, of the base wine, into a control glass and place it to the left hand area of the tasting glass orientation. (One should always taste against a control from left to right)
2. Pour the trials to be tasted, made in steps 5,6 and 7 above, in increasing increments in each wineglass progressing from left to right. Mark their contents.
3. Add to this flight any wines from past vintages you may want to review or any other blind samples from other producers you may care to use as a benchmark. Only do this step if needed. Mark their contents.
4. Taste and smell each wine several times. Go through the flight and detect what wine/juice may best match or improve the desired style one is trying to achieve. Review the chemistry data generated in step 8 above while tasting the trials.
5. Select the best match and leave the room for 1 to 2 hours so your palate may re-calibrate.
6 .Return and re-taste to confirm your previous decision with a fresh palate.
7. Repeat as often and needed.
Should chemistries play an important role to reviewing certain additions be certain to run a necessary panel of lab test to ascertain the proper numbers are also achieved. One may need to balance taste, flavor and chemistry to make some tough choices. Have all the data necessary and available to make those choices.
Calculation:
Once the fear of the metric system is overcome and confidence is achieved, the calculations become very simplistic. Let’s take the above as the example. If we dissolve 1.0 gram of tartaric acid into 100 milliliters of wine we now have 0.1 gram of tartaric acid in every 10 milliliters of wine. From this base if we blend 10.0 milliliters (one-tenth gram of tartaric) into 100 milliliters of the same fresh base wine – this represents the equivalent of one gram per liter. If we were to have used twenty milliliters that would represent two grams per liter in the small 100-milliliter blend. If we keep track of what we are tasting or testing and select the trial we prefer, one can mathematically calculate how much of the given addition is needed in a tank of a known quantity of juice or wine. One can also extrapolate this out to larger volumes in the laboratory should it be desired to work beyond a 100-milliliter sample.
Spicing it up!
Once the first set of trials is mastered one may build on to the next step projecting out what one may want to do with the juice or wine. This could eventually, and perhaps should, build out to treating large enough samples that one could cold and protein stabilize the wine in the lab, filter to the projected desired micron size and taste with a panel.
If tartaric acid is not giving the desired result – select other approved acids for that wine. Fruit wines, other than grape, often have other principal acids so one may need to explore using that principal acid first.
Double Checking the Results
From experience, one can get so creative in a lab it can be difficult to trace exactly how one arrived at a certain desired concoction. Copious notes should be taken throughout the complete process in the lab. Given a tank of juice or wine can often equate to hundreds of thousands of dollars or more it may be prudent to run the selected trial a second time, and compare, to confirm any additions before performing the action in the cellar. Be confident of what you are about to do.
Action in the Cellar
This is often the simple part. Using tartaric acid as an example for the addition one will simply calculate the amount of acid needed to match the desired trial. Weigh the desired amount of tartaric and dissolve in a bucket of warm water or wine from the tank. Once dissolved add slowly to the tank while mixing. Continue to mix until fully integrated and then select a sample from the sample valve for tasting, a quick pH and titratable acidity analysis. This will confirm the task or end result was achieved.
Summary
Given time and experimentation with this system many pH-lowering trials with additions will become easy and systematic. Trials will often take less than ten minutes to prepare and one may taste at several points during the day or use extra time to perform lab test to confirm desired objectives.
Other Helpful Tips
Keep in mind not to over scrutinize your accuracy in the laboratory. By this I mean make sure that if we measure something very exactly in the laboratory make sure this action will be able to be duplicated outside the lab. It is not uncommon, early on, for winemakers to get extremely exact in the lab only to step into the cellar with sloppy control over what they had just experimented with.
This system can be used for dosage formulation for sparking wines.
If accurate scales may be an issue the winemaker may always start by weighing larger quantities and dissolving into solution then breaking down that solution. Example: If a winemaker wants a 1.0 gram per liter solution and the scales are not accurate enough to weight one gram the winemaker may dissolve 10.0 grams into 100 milliliters and then measure out 10 milliliters of that solution and this should roughly equate to one gram.
NOTE: Make sure all solids are dissolved and dispersed equally into any solution.
One may also be able to blend two trials in 50% to 50% solutions to get an example of a trial in the middle without having to make one up specifically to match the amount desired.
Always remember your palate may become desensitized while tasting and to step away from tasting for an hour or two and then return to
taste ones preference. You may be shocked you had become used to (Desensitized) certain levels because of tasting such extremes.
Next issue: Raising the pH
References:
Amerine, M.A., Berg, H.W., Cruess,W.V. 1972. The Technology of Wine Making
Dharmadhikari, M.R., Wilker, K.L. 2001. Micro Vinification.
Zoecklein, B.W., Fugelsang, K.C., Gump, B.H., and Nury, F.S. 1999. Wine Analysis and Production
Verbal discussion with Mr. Jacques Boissenot, Mr. Jacques Recht, Mr. Joachim Hollerith and Chris Johnson.
