Wine Analysis
Hints and Tips
Distilled Water
Olive green/purple colour
H2O2 bulk indicator addition/adjustment.
Excessive flow rate and SO2 loss check.
NaOH (sodium hydroxide) storage and reducing loss of NaOH strength.
Sulphur Dioxide (SO2) additions
Using a carboy to apply a vacuum/suction
Working systematically
Using carboys to generate a vacuum and cooling water
Stock Solutions
KippsMeasures
Helpful hints and tips
Distilled Water
The use of distilled water is recommended to eliminate impurities or contaminations that can interfere with the analysis being performed and lead to errors.
Olive green/purple colour
When you are confident of having achieved the two colours involved in the hydrogen peroxide( H2O2) solution in the pear shaped flask during SO2 determination, keep aside two representative samples as colour standards, for later comparisons.
H2O2 bulk indicator addition/adjustment.
If doing a number of SO2 analysis, it will save time to add 4-5ml of mixed indicator solution to the prepared 100ml of 0.3 % H2O2 solution. You can then adjust the solution to an olive green colour using 0.1M HCl and 0.1M NaOH instead of 0.01M HCl and 0.01M NaOH as in step 5 of the SO2 determination procedure, as a bulk preparation.
This prepared, bulk hydrogen peroxide solution can be used for up to one week if kept stoppered and stored in a refrigerator.
Excessive flow rate and SO2 loss check.
The aspiration flow rate during SO2 analysis should be determined using a flow meter.
It is however helpful when learning to have two pear shaped flasks (with H2O2) set up in series as per diagram.
If any SO2 is not trapped in the first flask, it will be detected by turning the solution in the second flask to purple as it is acidified by the formation of H2SO4 (sulfuric acid), indicating a too fast a flow rate.
If the colour remains olive/green, it can be used for the next determination (e.g. BSO2).
While the second flask is used in your subsequent analysis (i.e. being aspirated for 15 min.), a titration can be performed on the first flask, saving time during this time consuming analysis.
Sodium Hydroxide (NaOH) storage and reducing loss of NaOH strength.
Solid NaOH (sodium hydroxide) pellets need to be stored in airtight containers as NaOH will take up moisture from the air and gradually liquefy.
Contact with carbon dioxide (CO2), in the presence of minimal moisture, will also react with NaOH pellets forming sodium bicarbonate as shown below.
NaOH(solid) < == > Na + (liq.) + OH-(liq.) + CO2 < == > HCO3- + Na+ <==> NaHCO
In the same way, NaOH solutions will lose strength if exposed to CO2 (carbon dioxide) from the air, utilising atmospheric moisture.
To prevent air contact, NaOH solutions can be stored in isolated delivery systems, utilising soda lime tubes.
Sulphur Dioxide (SO2) additions
Convenient additions of SO2 to juice or wine are best achieved by preparing a stock solution. The strength should be such that 1ml of stock solution added to 10 L of juice/wine raises the juice/wine by 10 ppm SO2.
Working systematically
- When working with a number of solutions during any chemical analysis it pays to work systematically.
This includes immediately closing of all bottles after use to prevent accidental spillage.
Leaving lids off can result in a mix up between similar lids with possible contamination of solutions.
- Dedicate a pipette per solution even if the same volumes are involved and pair them with each solution by placing them along side on the right hand side of each bottle.
This prevents confusion, contamination and allows continual re-use of pipettes when performing a number of analysis.
Using carboys to generate a vacuum and cooling water
- Arranging two carboys, as shown in figure 10, can supply both a vacuum to draw air through the Rankine Apparatus at the recommended rate and provide the cooling water flow through the condenser during BSO2 and TSO2 analysis.
- The flow rate can be determined by placing "Texta" graduating marks on the plastic carboys and timing the water flow rate or collecting and timing the run off in a graduated container.
Stock Solutions
- Preparation of stock solutions save time and allow for immediate additions when required at the correct rates ( see SO2 stock solution )
- Stock solutions can be prepared for trailing copper additions, acid addition for both taste and pH modifications.
- Stock solutions can also be prepared for easy, final additions and allow for thorough dispersion.
Kipps Measures
A Kipps Measure is a handy and safe measuring devise for approximate, standard volumes and repetitive additions (see diag.)
.
- In combination with conical flask it is recommended for Phosphoric acid (H2PO4) additions and hydrogen peroxide (H2O2) additions.