UGA Crop Quality Laboratory
Analytical Services for Wine and Grapes
Our goal is to offer analytical support for Georgia wine producers to monitor the quality of their entire winemaking process. The crop quality laboratory at UGA offers an array of analytical tests for grapes, juice, musts, and finished product which will benefit producers in a variety of ways:
• Confirm grapes are at peak maturity and contain preferred parameters
• Assess wine chemistry (i.e., acid, sugar, or tannin additions)
• Aid in correcting natural deficiencies (i.e. tartaric, malic acid additions)
• Measure stability
• Adhere to TTB regulations (e.g., alcohol concentration, volatile acidity)
• Troubleshoot suspected problems or flaws
• Maintain a history of the winery’s vintages
Grape and Juice Analysis
Analyzing basic chemistry parameters of grapes/juice can improve the efficiency of fermentation and avoid potential problems during the wine-making process. Without analytical data of the fruit or juice, winemaking decisions become guesswork, and any decisions, if made poorly, can have a detrimental impact on the wine’s quality.
Basic Juice Analysis ($100 per sample) includes:
• Titratable acidity
• Sugars (glucose & fructose)
• Yeast Assimilable Nitrogen (YAN)
• Malic acid
During and after the wine making process, there are several analyses that will give information pertaining to flavor, stability, and completeness of the fermentation process. Additional rounds of basic chemistry analyses should be completed if wines undergo and complete malolactic fermentation (MLF).
Basic Wine Analysis Package ($150 per sample) includes:
• Titratable acidity
• Volatile Acidity
• Free and Total Sulfur Dioxide
• Malic Acid
• Sugars (glucose & fructose)
Here is a list of individual parameters that the UGA crop quality lab is offering:
Purpose: A measure of hydrogen ion concentration, pH affects microbial stability, concentration of SO2, tartrate stability, and the perception of wine structure. Wine pH is in the range of 2.9 to 4.2
Purpose: Measures sugar content of grape juice which is used to determine optimal harvest time
Titratable Acidity ($15)
Purpose: A measure of the acids in wine that can be neutralized and corresponds to the sensory perception of acid strength. The range is 5 to 8 g/L.
Organic Acids ($20 per acid)
Purpose: Tartaric and malic are the primary acids found in grape wine that has not undergone malolactic fermentation. Wines are not considered MLF stable until less than 35 mg/L of malic acid remains in the wine.
Volatile Acidity ($20)
Purpose: A measure of acetic acid, whose abundance suggests microbial contamination and is considered a sensory flaw. Should be <1.4 g/L for reds and <1.2 for whites/dessert wines.
Purpose: Measures ethanol concentration which is a critical constituent of wine that can affect taste, microbial activity, and solubility of compounds. Up to 18% in finished wine and up to 24% in dessert wine.
Residual Sugars ($40)
Purpose: Quantification of fermentable sugars (glucose & fructose) which gives an indication of a wine’s dryness. A dry wine may have no detectable reducing sugars while sweet wines may be in excess of 30 g/L.
Free SO2 & Total SO2 ($30)
Purpose: Sulfur dioxide is used as an antimicrobial and antioxidant in wine production. Concentrations above 10 mg/L require the label to include a warning. Should be <350 mg/L.
Purpose: Impacts the color of red wine and plays an important role in tannin retention in and aging. Typical values for red wine are 150 mg/L.
Yeast Assimilable Nitrogen ($20)
Purpose: To gauge whether additional ammonium is required for fermentation which can impact flavor and quality of wine. YAN values <150 mg/L can result in stuck fermentation while high YAN (>450 mg/L) can negatively impact clarity and flavor.
Trace Elements ($50)
Purpose: The concentration of dissolved analytes can affect wine stability. Excess calcium and potassium can promote tartrate precipitation, and copper and iron favor oxidation. Copper concentrations cannot exceed 0.5 mg/L.
Top sampling involves lowering a bottle (via an attached nylon cord) down through the wine such that it fills on the way to the bottom. An examination of the wine surface should be conducted to determine the presence of film yeast and acetic acid bacteria. Adjust how fast the bottle is lowered so that is fills from several areas in the tank. If taking a sample from the valves, clean the valve by rinsing with water and allow approximately 1 liter of wine to flush through taking the sample.
Check the bung area for signs of microbial growth, looking for stains or spills, looking for film on the surface of the wine with a flashlight and checking for VA smell. If the barrel was properly sealed a vacuum should have been created. If, when the bung is removed, vacuum pressure was not noticed, check to see if the barrel is leaking or if there is some reason for improper bung closure. A clean and sterile wine thief is best used for removing barrel samples. Wines in individual barrels may have significant differences in their chemistry and biological content, so it may be good to sample several barrels and combine them or have them tested separately.
Getting samples to the lab:
For grape/juice package analysis, mail approximately 100 berries or 100 mL of juice in a plastic container. Over-night shipping is recommended. For wine analysis, we need approximately 1 liter of wine to complete the full package test.
Print out the submission form located here: http://aesl.ces.uga.edu/forms/ChainOfCustody.pdf
Write the description of the tests you would like in the “Analysis” column.
Mail them and sample(s) to:
UGA Crop and Environmental Quality Lab
2300 College Station Road
Athens Ga, 30602