Measurement Uncertainty (MU) Data

For Measurement Uncertainty (MU) data for accredited method results please contact us on 1300 302 242

 

Preparing and Sending Samples

Use the Free Winechek EasyTest Sample System to send your samples to your nearest laboratory. This system has been designed to make sending test samples simple, while protecting your sample integrity.

The Winechek EasyTest Sample Kit includes:

- 50mL sample vials

- Pre-printed test selection labels

- Pre-printed Reply Paid Address labels

How to use your Winechek Easy Test Sample System:

1. Fill Sample Vial

- Fill the sample vial, close the lid firmly and check for leaks. If leaks occur, some adhesive tape around the top can help.

- For a number of different tests on one sample, more than one vial may be required. Sample size is noted in each test. For some testing it may be necessary to send a full bottle.

- Fermenting Samples: The sample vials are rated to 2 bar pressure. To ensure your sample’s integrity, do not send wine that is fermenting! If necessary, add SO2 to stop the fermentation.

2. Select Tests Required

- Write sample details onto pre-printed test selection label, tick the test/s required, and stick to vial.

- If you do not have enough labels, or need more space, you can include a note with your samples, or email us: info@winechek.com

3. Sending Samples

- Pack samples securely – padded envelopes or foam boxes are recommended.

- If sending more than one package, tape them together to ensure they arrive together.

- Australia Post have requested that customers do not send glass containers unless in a foam pack. If a breakage does occur then Australia Post will hold the sender liable for damage to any other postal items.

FREE SULFUR DIOXIDE SPECTROPHOTOMETER TEST KIT

FREE SULFUR DIOXIDE DISCRETE ANALYSER TEST KIT

One of the most crucial factors in enzymatic analysis is volumetric accuracy. Taking care to properly use and maintain micropipettes will save you time, money and frustration in the long run.

It helps to pre-wet new pipette tips by aspirating and dispensing the liquid before pipetting.  This forms a thin film on the inner wall of the pipette tip, and guarantees precision across all assays (otherwise the first volume dispensed would be too low).

To pipette, press the pipetting button to the first stop only.  Hold the pipette vertically when immersing into the liquid.  Avoid using the pipette on a horizontal angle, as liquid may enter and contaminate the shaft.  When aspirating, allow the button to slide back slowly to avoid splashing or bubbling, and wait 1-2 seconds before removing.

When you are ready to dispense the sample, press the button slowly to the first stop, pause and then blow out the final volume by pressing the button all the way down to the second stop.

During vintage you should check the condition of micropipettes weekly.  Make sure that the shaft is free from contaminants and has not become blocked.  Check that the tips fit snuggly, and that the piston seal is secure, by aspirating a sample and holding the pipette vertically for 10 seconds.  If liquid drips out of the tip then maintenance may be required.  Try to store pipettes in a vertical position (on a rack) rather than lying down.

Check the precision of your pipettes every 3 months.  You can simply place a beaker on a lab balance, set the pipette to its maximum volume (or the volume it is mostly used at), and then pipette some distilled water into the beaker (remember to pre-wet the tip!)  Record the mass and repeat several times to check repeatability.  1mL of distilled water weighs approximately 1g, however you will need to  apply a correction factor for temperature and altitude to convert the mass obtained to a volume.

Under ideal conditions, the maximum error is 3% for most micropipettes in the range of 10µL to 1000µL.  If you are concerned that a pipette is not functioning properly, you can follow the calibration procedure available on our website  or have it cleaned and calibrated at your nearest Winechek laboratory.

TOTAL SULFUR DIOXIDE SPECTROPHOTOMETER TEST KIT

You use them every day for your enzymatic analysis and probably don’t think too much about them. But the quality and correct use of your disposable cuvettes are critically important for ensuring accurate enzymatic or colorimetric results.

We use high quality disposable cuvettes in our NATA accredited labs, for analysis as well as for validation of our Test Kits. These are the same cuvettes available on our website store for you to purchase.

A few things to consider when next using cuvettes:

• Watch out for scratches or small etches on plastic cuvettes, these can affect your absorbance readings.
• Glass and plastic cuvettes are suitable for use in the visible wavelength range.  Quartz cuvettes should be used for measurements in the UV range.
• Cuvettes have two opaque surfaces for handling purposes.  Avoid touching the optical windows, but if they do become dirty, then wipe with a soft cloth or lens tissue.  Do not wipe with paper tissues as they are abrasive and may leave fibre residue and brightening agents on the optical windows.
• Tap out any air bubbles caught in the solution in the cuvette prior to taking an absorbance reading.
• It is not recommended to wash and reuse plastic disposable cuvettes.

Total SO2 CW-T DA Fact Sheet

Absorbance readings taken from spectrophotometers during enzymatic analysis should be considered carefully before they are used to calculate important wine parameters.

Many spectrophotometers have a photometric range up to about 3.0 absorbance, but this does not necessarily mean that any value up to 3.0 is an accurate reading.

Spectrophotometers don’t directly measure absorbance, they actually measure the light that is not absorbed by the sample and transmitted to the photometer. The relationship between absorbance and transmittance is exponential, at an absorbance of 1.0, 10% of light gets through the sample and is detected. At an absorbance of 2.0, 99% of light is absorbed and only 1% of light is detected. When measuring very low levels of transmitted light, even small variances in photometric accuracy can have a big impact on the final result.
As a rule of thumb, it is prudent to accept absorbance readings below 1.5 units only.

Dilution factors, red wine decolourisation and sample clarification are some of the factors to consider when preparing enzymatic assays.

Introduction
The following is an expanded version of the talk given by Steve Byrne at the Interwinery Analysis Group seminar in Adelaide on Friday 1 August 2014. The topic presented was ‘Advances in Ebulliometry and Tips for Improving Precision’.

Background
Ebulliometers have been used for measuring the alcoholic content of wine since the late-1800s. The traditional manual model is still in production and newer electronic versions are now also available.

Ebulliometers are still commonly used in wineries, particularly small wineries, because ebulliometers:
-are relatively inexpensive
-are easy to use
-are quick to get a result
-do not require any power as they use a spirit burner
-require no consumables except distilled water
-look cool and are fun to use!

Figure 1: The traditional ebulliometer, still in production

Figure 2: An electronic ebulliometer

More detailed discussion on how to use ebulliometers and other ways of measuring alcohol have been published in this journal previously (1,2).

The focus of this article is on the main drawback of using an ebulliometer and that is the accuracy. And this, of course, can be quite a disadvantage for such an important parameter.

Measuring alcohol (ethanol) in wine by Ebulliometry is not an officially recognised technique by either the International Organisation of Vine and Wine (OIV) or AOAC International. These international bodies are sources of official test methods and although they have other techniques for determining alcohol in wine, ebulliometry is not one of them. We can only assume this is because of the accuracy of the ebulliometric technique.

Theory
An ebulliometer is a simple device for measuring the boiling point of a liquid. The derivation of the word ebulliometry is from Latin ebullire “to bubble up”. For pure liquids the accuracy is very good, however for non-pure liquids the determination is more complicated. This is because of the well-known colligative property of boiling point elevation in the presence of dissolved substances (solutes). Changes to the atmospheric pressure also affect the results and this must be taken into account as well.

For a mixture of pure water and pure ethanol the proportion of alcohol can be found with good accuracy. However if dissolved substances such as organic acids and sugars are present (as in all wines) then a correction must be applied. For very dry wines the results can be good, however in the presence of high levels of sugars the boiling point of the solution is elevated and has to be corrected, and this can lead to unacceptable errors.

Improving your technique
There are some ways that the accuracy of results from ebulliometers can be improved: before measuring the boiling point of your wine, you first need to ‘calibrate’ the ebulliometer by measuring the boiling point of a liquid of known alcohol concentration. Historically, distilled water has been used to calibrate the ebulliometer for the obvious benefit of it having a known alcohol concentration of 0%v/v.

This however can lead to inaccuracies in your sample results as you are calibrating with a solution that has a far lower alcohol concentration than your samples and also has a matrix very different to your wines. Trials have shown that when calibrating with distilled water, the higher the alcohol content of your wines, the greater is the error in the results (see Figure 3).

 

For higher alcohol wines, precision can be improved by diluting the wine with distilled water, by say 1:1. This has a two pronged effect. First, it reduces the error associated with the presence of solutes in the sample as the impact is halved. Secondly, by lowering the alcohol you are measuring at a level that is closer to the calibration point of 0%v/v.

Diluting your samples can have its own drawbacks though. Dilution errors can impact on the final result - the extent of the error depends on the level of accuracy of your volumetric glassware and the lab technician performing the dilution.

So rather than calibrating the ebulliometer with distilled water, a better approach is to calibrate it with a stable wine sample of known alcohol concentration, otherwise known as a “standard wine”. This is best obtained from a NATA accredited laboratory. This standard wine will be much better matrix-matched to your samples and have an alcohol concentration closer to your samples, thus improving accuracy (see Figure 4).

Other techniques for measuring alcohol: Distillation
Another technique for measuring alcohol in wine that is suitable for small to medium wineries is distillation. The cost for setting up and operating this is about the same as for ebulliometry, however this technique is:
-more accurate
-officially recognised by the OIV (inferring it is of sufficient accuracy)
-has very low consumable costs

The major disadvantages of the distillation technique are that:
-it is more time consuming than ebulliometry
-it requires better technical skills
-if used with a pycnometer (weighing bottle) it requires an accurate balance
-or if used with a hydrometer then this requires calibration
-it is glassware-based and so the apparatus is more fragile

The best technique (but most likely out of the range of most small to medium wineries due to the A$20k price tag) is a Near Infra-Red (NIR) spectrometer. This is the method we use in our laboratories. These are great pieces of equipment as they are:
-fast
-easy to use
-very accurate
However they do require very good skills to correctly calibrate them daily.

Label alcohol statements
For the label alcohol statement we strongly recommend that you have the alcohol content of the wine analysed by an accredited laboratory, regardless of the technique you use in your winery laboratory.

We have been performing Export Certification of wine in Australia since 1996 and have lost count of the times that we have received fully labelled and finished wines only for us to get an alcohol content that differs greatly from what is on the label. For the sake of paying an accredited lab around $20, it just isn’t worth doing the alcohol label statement yourself!

Conclusion
Ebulliometry is a technique that has been used for over 100 years for measuring the alcohol content of wine. There are some simple ways to improve the accuracy of this technique. There are also other more accurate ways to determine alcohol. It is strongly recommended that whatever technique you use, you get the label alcohol content determined by an accredited laboratory.

References
1. Bowyer, P.K; The measurement of alcohol levels in wine, The Australian Grapegrower and Winemaker, Annual Technical Issue 2006, 90-96

2. Vallesi, M; & Howell, G.N; Which alcohol analysis method should you use? The Australian Grapegrower and Winemaker, 2002, 467, 53-56

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