Greg Howell
Vintessential Laboratories
Introduction
Some, but by no means all, samples we receive in our laboratories cause quite a bit of interest for us and quite some angst for our winemaker clients. These samples and how they are tested can present some interesting case studies in what can go wrong in the winemaking process. Below are some more recent examples of how we work with winemakers to investigate problems in winemaking and how, together, we find solutions. Not all samples we are sent are wine samples – in this article we discuss how a cider sample caused some issues as well.
Botrytis in Chardonnay and possible stuck ferment
A customer had Chardonnay fruit that had some Botrytis infection. He also had concerns about the fermentation kinetics. We were asked to test for laccase enzyme activity and also for the presence of glucans, plus recommendations of products to assist with fermentation.
The winemaker had completed a bench test to obtain a qualitative result – the sample had been poured into two wine glasses and covered; one sample was placed in a fridge and other left out for 24 hours. The two glasses of wine were then compared for changes in colour. The non-refrigerated sample was browner, indicating laccase activity. The results of our tests indicated medium laccase activity and high glucan levels.
The treatment recommended was the addition of a complete yeast nutrient (Maxaferm) to help fermentation reach completion, and treatment with a glucanase enzyme product (Rapidase Batonnage) to allow the glucans formed by the Botrytis to be degraded. Once the glucanase treatment was complete (as checked by benchtop trials), Bentonite fining was used to remove the laccase enzyme and then more sulfur dioxide was added. Testing for gluconic acid in the other ferments that may be affected was also recommended.
Titratable Acidity differences between the client’s own lab and our lab
A customer had been doing their own testing of Titratable Acidity (TA) on their wine samples and was consistently getting higher TA results than ours. To find out what was causing the difference, a comparative analysis of TA on samples they had already analysed in their own lab was done in one of our labs.
Upon discussion with the customer, it became apparent that there were several steps in their in-house procedure that could be having an impact on their results. The impact of each in isolation would be minor, however each one would create a bias towards a higher result and so had a cumulative effect.
The issues were:
• not degassing the finished wine
• using 10.00 mL of wine diluted with distilled water
• the distilled water not being degassed or neutralised prior to use
• the 0.1M NaOH was not standardised before use
To resolve the issue we recommended the following changes to the procedure used by the client:
1. Degas the wine. This is a standard step and removes the carbon dioxide which forms the weak acid carbonic acid in water, thus adding to the overall acidity of the sample. Our experience is that many winemakers skip this step.
2. Consider using 25.00 mL of sample. This ensures there is enough volume in the sample container to cover the pH electrode with sample without having to add distilled water. And so it also avoids the extra work of ensuring the distilled water is neutral.
3. Use 0.333M Sodium Hydroxide instead of 0.1M. The benefits of this are that the pH and TA can be done sequentially on the same 25.00 mL of sample. Other benefits are that the more concentrated 0.333M NaOH has greater stability than 0.1M NaOH with respect to absorption of carbon dioxide from air. And finally using 0.333M means that the volume of titrant used is simply the value for titratable acidity without having to apply a multiplication factor.
The customer changed their method to what we had suggested and started getting TA results consistent with ours.
Crystalline deposit in bottled wine
A white wine was submitted which had developed a deposit in the bottle that looked crystalline in nature. The wine had been treated with a carboxymethyl cellulose (CMC) product and had been thought to be potassium bitartrate (KHT) stable. However, the winemaker requested that the cold stability test be carried out to check this. The cold stability test (72 hours at -4oC) was carried out on a filtered sample of the wine (that is without the crystals) and the wine was found to be cold stable.
The winemaker felt that it was unlikely that the deposit would be calcium tartrate as no calcium products had been used in the winemaking process and none that he knew of had been used in the vineyard. However, after discussion, he requested that further tests be carried out on the deposit to determine what it was.
Our investigations revealed that the deposit was indeed potassium bitartrate. Since the sample tested in our lab was found to be cold stable it appears that the wine was not cold stable at the time of bottling and had then precipitated KHT in the bottle. Once the KHT had precipitated out, the wine in the bottle was then cold stable. The winemaker unfortunately decided that the only course of action was to re-filter and re-bottle this wine.
Cider sediment
We recently received a cider sample that contained a large amount of white sediment. The customer was concerned that it was precipitated concentrate that had been added to the cider, or that it was a microbial contamination.
The customer was interested in testing alcohol, carbon dioxide and doing a sterility check; however since we only had limited sample volume we suggested that we could do a micro deposit identification test to try to establish what was in the sediment.
We therefore went ahead with the micro deposit identification and upon examination of the sediment under the microscope we identified that the deposit contained yeast cells. We then plated some of the sediment onto WL agar plates to determine whether these cells were viable. After a few days of incubation, growth was observed on the agar plates and microscopic examination confirmed the presence of viable yeast cells.
It was recommended that the customer filter the cider to remove the yeast cells and add the appropriate level of sulfur dioxide; these steps making it unlikely that any re-fermentation could occur.
Conclusion
There are always samples that are submitted to a specialist fermentation beverage laboratory such as ours that call for collaborative attempts to solve problems for the producer. As can be seen above, most of these issues can be resolved using some advanced testing techniques and in some instances, particular winemaking products can be employed to ensure good quality stable wine.
Greg Howell founded Vintessential Laboratories in 1995; he can be contacted by email on [email protected]. More articles on related topics are available on the Vintessential website: www.vintessential.com.au/resources/articles/
