Common Troubleshooting, some hard won notes

Transcription

1 Common Troubleshooting, some hard won notes Eric Wilkes Leanne Hoxey and many others

2 Troubleshooting The problems are solved, not by giving new information, but by arranging what we have known since long. Ludwig Wittgenstein, Philosophical Investigations

3 SO 2 - Aspiration Peroxide solutions go off in heat and light. Poor quality water gives poor indicator colour and degrades peroxide Putting the indicator in your peroxide supply will make it deteriorate more quickly High gas rates and boiling solutions can carry over droplets of wine and VA giving false highs. Low gas flow leads to low results. Temperature is important. NaOH solutions do change with time (restandardise) Excessive vacuum grease absorbs SO2. Adding orthophosphoric acid too soon before aspirating can lead to low results Air bubbles in burettes (particular hidden ones in digital burettes) leads to titration errors

4 SO 2 - Aspiration Residue detergent can react with SO 2. Positive pressure systems can leak but are easy to balance gas flows. Vacuum systems don t leak, but are much harder to balance gas flow. Blowing through the bubbler tube can dissolve carbonic acid leading to end-point changes Dripping wine and juice can stuff up Bunsen's.

5 ph/ta Don t reuse buffers, cross contamination stuffs them. Calibrate as close to 20 deg as possible. Temperature correction does not adjust for the sample, titrate at 20 deg always. You can dilute your sample volume, but only for TA not for ph. Porous frits block! Fast flow junctions do just that, and run out of electrolyte. Pay attention to the zero point and slope (graph them). Pay attention to the stabilization time (set a limit). For autotitrators, slow stabilization can lead to missed end points.

6 ph/ta Use a tartrate solution for a QA check, not HCl. Always run a standard add sample to check performance. Carbonate build up (the white powdery stuff) screws up the mechanics of autotitrators and syringes. NaOH deteriates through interaction with atmospheric CO 2. Standardise regularly. Use a lime trap on the NaOH reservoir. Never trust premade solutions! Improper degassing causes some of the biggest errors (validate you method). Don t leave the electrode storage plug in when in use Clarify juice samples by centrifuging if necessary Be diligent with electrode cleaning during vintage to avoid protein build up

7 Alcohol (hydrometry) Low quality water can impact alcohols by distillation. Water temperature in the condenser can make a big difference, either chill or have a decent flow rate for tap water. Use a slow boil no matter how much of a hurry you are in. If you turn your back on it, it will go over the mark! Hydrometers don t bounce. Badly scratched or small cracks can make a hydrometer inaccurate. Clean hydrometers with methanol and than distilled water after each use. Adjust high VA or SO 2 wines to ph 8 with Ca(OH). Chill the receiving flask. Make sure the receiving flask is away from direct sunlight or heat.

8 Alcohol (hydrometry) Bring the receiving flask to 20 deg before making up to the mark. Make sure the hydrometer flask is not too tight or too loose. Use anti bumping granules. 1 or 2 is enough. Use of antifoam Use smaller volumes to distill samples with high alcoholic strengths (> 30% v/v) Calibrate hydrometers regularly

9 Alcohol (ebulliometer) Keep it spotless. Changes in atmospheric pressure will stuff up the results. Do standards and results together. Make sure standards are within 1% of the measured wine. Replace the condenser water for each test. Make sure you take the reading at the first stable point. High sugar samples need corrections.

10 Alcohol (NIR) Never leave wine in the cell, even for a little while. Always rinse with water after each set of readings. Be careful with strong detergents, they can damage the cell. If doing lots of high protein wines you can get a build up, clean occasionally with pectolytic enzyme. Despite what the brochure says, turbid samples can give weird results (and block the cell). Micro-tartrate crystals (off cold stab) can give high results.

11 Alcohol (NIR) If lots of dirty wine has been put through the cell can be partially blocked leaving dead spots. Measure close to 20 deg, the cell heating/cooling can only do so much. Run regular zero and standards (graph results). Constantly correcting the zero means there is a problem. Hand degas sparkling samples (effects of air bubbles on stable readings) Use syringes without rubber end on plunger (can draw forwards bringing air into system)

12 VA (Steam distillation) Crap water, crap result. Poor water can make the end-point harder detect. The peroxide goes off very easily, replace very regularly, keep in fridge out of light) M NaOH can change quite quickly through interaction with CO 2 in the air, standardise and check regularly. Make sure the flow rate to the condenser is sufficient (i.e. it shouldn t get warm). Neutralise the water in the receival flask. Degas the wine carefully, too much and you lose VA, too little and the CO 2 will interfere. Run a known sample or standard regularly to check for leaks. Use the minimum amount of vacuum grease. Air bubbles in burettes (particular hidden ones in digital burettes) lead to titration errors

13 Reducing sugars (Lane & Eynon) Run a standard or known sugar solution with each batch Sugar solutions have short shelf lives consider freezing aliquots Fehlings A and B mix must be freshly prepared Decolourising reds is a must not too much or too little carbon Ensure boiling / titration time for reaction is consistent (3 mins) Mixing is important during titration boiling chips or stirrer bars Missing the brick red endpoint titrate dropwise near endpoint Use a white background to help determine the endpoint Calculate 75% of titration volume for higher sugar samples to avoid overshooting titration or exceeding titration time Air bubbles in burettes (particular hidden ones in digital burettes) lead to titration errors Dilutions samples containing > 4 g/l reducing sugars

14 Reducing sugars (Rebelein) Run a standard or known sugar solution with each batch Sugar solutions have short shelf lives consider freezing aliquots Solutions Z1 and Z6 are the most unstable do your own trials to establish expiry dates for all Use purified water for all Rebelein solutions Use plastic stopper for storage of Rebelein solutions Decolourising reds is a must not too much or too little carbon Ensure boiling chips are used to mix during heating Allow solution to reach room temp before adding Z3, Z4,Z5 Titration must occur within 3 mins of adding Z3, Z4 and Z5 Missing the cream endpoint titrate dropwise near endpoint

15 Reducing sugars (Rebelein) Calculate 75% of titration volume for higher sugar samples to avoid overshooting titration or exceeding titration time Air bubbles in burettes (particular hidden ones in digital burettes) leads to titration errors Invert sugars is there sucrose in the sample? Dilutions samples containing > g/l reducing sugars If using microwave to heat, check solution actually boils and validate heating times required

16 Enzymatic tests Run a standard add sample in each run as well as a known sample (not a calibration standard). Run regular calibration curves (they should be very close to linear) One dilution does not suit all (avoid curves). Enzymatic samples go off in high temperatures, monitor standard response. Temperature matters. The pipetting steps can give huge errors, make sure everyone is using the autopipette in the correct manner. Don t reuse tips between samples. Ensure proper mixing. For big runs split into batches, time differences can have an impact. Regularly check spectro wavelength and absorbance performance. Storage of reagents to prevent contamination and degradation (eg clean plastic / fridge) Centrifuging or filtering of turbid juice or wine samples

17 Brix / Baume Hydrometer and density meters don t bounce. Have a consistent degassing procedure that everyone uses. Calibrate hydrometers and density meters regularly with known sugar solutions. Try and avoid solids. Clean density meters and hydrometers after each series of tests. With refracts temperature adjustment usually only adjusts for the instrument temp, not the sample. Measure close to 20. Make sure the thermometer temperature has stabilized before taking the reading when adjusting hydrometry. For hydrometers, make sure the measuring cylinder is not too tight or loose. Check hydrometers regularly for scratches and cracks. Check density meters for condensation on the u-tube. Refrac method not suitable for ferments or wine (alcohol interference)

18 And just one more thing! Broken glass cuts Don t let the results books out of the lab Clean labs have less problems Loose pieces of paper always go missing Don t lend equipment (pipettes / hydrometers etc) to untrained staff i.e. Winemakers and cellarhands! Occasionally it is good to be silly!