Several benefits from routine analysis include:
- Confirmation that harvested fruit has reached full maturity
- Obtain the appropriate data to make decisions in altering wine chemistry (i.e., acid, sugar, or tannin additions)
- Monitor and manage the microflora associated with each wine, and improve microbial stability
- Make decisions in terms of which filtering techniques are appropriate
- Adhere to TTB regulations (e.g., alcohol concentration, volatile acidity)
- Have wines analyzed to meet exporting regulations
- Confirm a suspected problem or flaw within a questionable wine
- Enhance the winery's record keeping of each vintage
These benefits, among others, contribute to an enhancement of wine quality. Having available data takes pressure off of the winemaker and cellar personnel to remember the data associated with each wine, and it can be used as a powerful tool to make commercially viable wines.
Some wineries may find it challenging to adequately maintain an in-house analytical lab and hire an experienced enologist to monitor quality control associated with their production. Luckily, there are several wine analytical labs available to support the wine industry across the U.S.
The use of wine labs becomes essential during the harvest months. Analyzing basic chemistry parameters of incoming fruit or juice can improve the efficiency of fermentations in addition to avoiding challenging situations like stuck fermentations or the production of hydrogen sulfide. Without baseline data of the fruit or juice, winemaking decisions become recipe-like, and winemakers may make "on-the-fly" decisions without knowing the appropriate information. Such decisions, if made poorly, can have a detrimental impact on the wine's quality.
Several analyses should be considered for every incoming lot of grapes or juice:
- Basic chemistry parameters of the fruit or juice(pH, titratable acidity, and °Brix)
- Quantify the starting yeast assimible nitrogen (YAN) [ammonium + primary amino acids]
- Quantify the starting malic acid concentration to allow for decisions on which yeast strain should be used or if a co-inoculation of yeast and malic acid bacteria is appropriate
- Establish the microbial stability and potential threats of the incoming product, which can easily be assessed with a microscopic evaluation
These considerations translate into the following analyses:
- titration (for titratable acidity, or TA)
- sugar by refractometer or hydrometry
- YAN analysis
- malic acid analysis
- juice evaluation under a microscope
Mailing Juice Samples to a Wine Laboratory
When sending juice samples to a wine lab, remember that the juice should be in a plastic container. This is for the distributor's and lab employees' safety. Remember that juice can ferment spontaneously, especially under the right temperatures. Having the sample in plastic, as opposed to glass, ensures that the sample will not break and create a hazard while in transit. Additionally, overnight shipping is recommended for juice samples.
Many ISO-accredited laboratories have the policy that they must run the juice sample the day it is received. For this reason, winemakers should receive data on their juice samples the following day from shipment (assuming the lab is open and that the sample was mailed with overnight delivery). Winemakers are encouraged to check available hours of each wine lab before shipping samples.
Monitoring fermentation is typically done by using a hydrometer to watch the sugar concentration drop over time. Near the completion of fermentation, it is recommended that wineries use Clinitest kits to test for low residual sugar concentrations. However, for complete assurance that the wine is indeed "dry" (< 1 g/L of residual sugar), using an enzymatic analysis is the most accurate testing method. At this stage, wineries may have to consider submitting their finished wines for analysis at a wine lab. Wines with a lot of residual sugar or "stickies" will require an alternative analysis to compensate for the higher sugar content.
Note that refractometers are not recommended for a fermenting product as the ethanol will interfere with the reading produced by the refractometer.
In small wineries, alcohol can be measured by an ebulliometer. For more accurate ethanol analyses, wineries can send samples to an ISO-accredited wine laboratory.
At the end of primary fermentation, the basic chemistry analyses that a winery should record include:
- TA (g/L tartaric acid)
- % Alcohol
- Volatile Acidity (VA, g/L)
- Free and Total Sulfur Dioxide
- Malic Acid Concentration
- Residual Sugar Concentration
- Microscopic Evaluation
Another round of basic chemistry analyses should be completed if wines undergo and complete malolactic fermentation (MLF). Depending on when the wine was inoculated or started MLF, several chemical indices may vary compared to the end of primary fermentation. This is why it is a good idea to have the wine analyzed both before and after MLF. Indices that tend to change during MLF include pH, TA, malic acid concentration, and VA. However, if the wine had not completed primary fermentation, the winemaker may also see a change in things like the alcohol percentage and residual sugar concentration. MLF is considered complete when the malic acid concentration is less than 30 mg/L of malic acid.
It is okay to contact a wine lab to ensure that the winery is ordering the appropriate tests done for wines being submitted. Most labs have technical staff on hand to answer these types of questions. Furthermore, many labs offer additional services for more specific chemical analysis (e.g., tannin content) or for microbial analysis (e.g., culture plating, PCR). Some labs may offer sensory analysis or troubleshooting services to help fix a problem wine for a fee.