Acid Testing Basics

Introduction

Maintaining a proper acid balance is a crucial element of winemaking as it has a large impact on the flavor and character of the wine.  Wines or grape juices that are too basic, lacking in acid, can have a flat and bland flavor that lacks character and aroma.  Too much acidity in the wine or juice can leave a tart, sour or bitter flavor.  By testing the acidity of grape juice one can determine the perfect time to harvest for optimal flavor, as acidity increases during berry growth and begins to decline once veraison (ripening) begins.  Testing for acid levels of wine, prior to fermentation, will help optimize your fermentation environment and have a positive impact on the flavor, character, bouquet and longevity of the end product.

Malic Acid Testing

The two most popular acid tests are Malic Acid Tests and Titratable Acid Tests.  Malic Acid Tests are used to determine when a wine grape is ready to be harvested, as Malic Acid increases during the growth stage of the berry and rapidly decreases as the berry begins to ripen.  By monitoring these levels, in conjuction with Titratable Acid, pH, and Sugar Content, the ideal time to harvest can be determined. 

The primary use for Malic Acid Testing in home winemaking is for monitoring Malolactic Fermentation, also called secondary fermentation, which is the conversion of L-malic acid to L-lactic acid.  Malic acid is very tart, and its conversion helps the wine develop smooth, full-bodied, mellow flavor often associated with quality red wines.  Malic Acid Tests determine when this conversion is occurring, and most importantly, when it has completed.  Malolactic fermentation also increases concentrations of diacetyl, acetaldehyde, acetoin and 2,3-butanediot which are flavor-inducing compounds that increase the complexity and character of the wine.  Lastly, malolactic fermentation provides microbial stability to the wine – experienced winemakers prefer this secondary fermentation to finalize as soon after primary (alcoholic) fermentation has ended as possible, so that finishing steps can be completed to protect the wine from unwanted microbe activity.

The Malic Acid Test Kit we sell from Accuvin is extremely easy to use, and can test for Malic Acid concentrations down to 30 mg/L, which indicates the end of Malolactic Fermentation.  Simply:

1.  Take up a sample using the supplied Sample Bulb.
   
2.  Squeeze the sample on to a supplied testing strip (comes with 10 strips).
3. Compare the color of the testing strip to the supplied chart.

The kit comes with more detailed instructions and information to ensure a high degree of accuracy, as well as a chart for determining optimal acidity levels during various stages.

Titratable Acid Testing

Titratable Acid Tests generally test for the amount of Tartaric acid present in juice, wine or must.  Like Malic Acid, Tartaric Acid increases as a grape berry grows and declines after they begin to ripen.  Tartaric Acid decreases less rapidly than Malic, and is a great indicator for the optimal harvest time.  Monitoring and controlling Tartaric acid is a crucial step in optimizing the flavor and character of your wine, and testing should occur at all stages of production but especially prior to fermentation to ensure an optimal environment. Post fermentation, controlling your Titratable Acid levels ensures proper balance and helps with the aging process.

Titratable Acid Tests use titration of grape acids by sodium hydroxide (lye), which is a strong base.  The testing procedure is very straight-forward and simple, and all of our testing kits and supplies have detailed instructions and acidity recommendations to follow. 

Our Acid Test Kit for Titratable Acid comes with a 12cc Syringe, Testing Vial, Eye Dropper, Sodium Hydroxide, Phenolphthalein, and complete detailed instructions for accurate testing.  Its basic procedure is as follows:

1.  Measure 15cc of wine, must or juice with Syringe and place into Testing Vial.
2. Place three drops of Phenolphthalein into the Vial using supplied Eye Dropper.
3. Rinse and dry Syringe, then fill with 10cc of Sodium Hydroxide.
4. Add Sodium Hydroxide 1 drop at a time , which will change the color of the wine sample temporarily (white wine/juice turns pink, red wine/juice turns grey), and agitate Vial after each drop or two.
5. Continue adding Sodium Hydroxide slowly until the color change is permanent.  This indicates the titration is complete, and the acid has been neutralized.
6.  Measure the amount of Sodium Hydroxide used (you began with 10cc), then determine the acid level of the sample using supplied chart.

For example, if 5cc of the Sodium Hydroxide solution was used from the Syringe, the acid level of the sample is 0.50% (or 5 g/L).   A chart with ideal acid levels is included, for instance Red Grape Wines prefer an acid level of about 0.70%.

The Accuvin Titratable Acid Test Kit works in the same manner chemically, with a slightly simpler procedure.  Its results are given in g/L of Tartaric Acid, which can be easily converted to a percentage (example: 3 g/L = 0.30%).  Simply:

1. Take up sample of juice/wine/must with supplied Sample Bulb (comes with 10 bulbs).
2. Squeeze the sample into supplied vial containing Sodium Hydroxide and indicator (kit comes with 10 of these premade, sealed vials).
3. Compare color to the included color chart to determine acidity. 

This kit also comes with more detailed instructions and information for user accuracy.

Click Here for a complete list of Acid Testing Kits and Supplies