Deciding on the scope of operation of the laboratory
The level at which the laboratory will be operating should be defined first, which will then indicate the needs of the laboratory. Once this is decided, the type of equipment that is required can be specified and the space and service requirements can then be detailed.
As a guide, typical laboratory determinations that could be undertaken at various levels of operation are presented in the table below.
| Level | Matrix | |
| Grapes | Wine | |
| Basic | Total soluble solids, SO2 | pH, titratable acidity (TA) |
| Preliminary | + pH, TA | + alcohol, sugar, SO2, volatile acidity, density |
| Intermediate | + total anthocyanins | + MLF (qualitative), heat and cold stability, microbiological, filterability |
| Advanced | + organic acids, cations, anions, agrochemicals, glycosyl-glucose (G-G) | + organic acids, cations, anions, trace elements |
The following sections will discuss each level in more detail and describe the facilities required to perform various analytical procedures. Answering the following questions should be helpful to establish the level of operation at which you wish to operate:
- What do you want to measure and why?
- What technique do you want to use and equipment will you need?
- What level of laboratory skills and staffing will you need?
- How much money will you need to spend?
- Is there sufficient room for the laboratory and its equipment and staff?
Basic level
Grapegrowers are often paid according to the concentration of sugar, measured as total soluble solids (TSS), of their grapes as determined usually at the time of delivery to the winery. It might be useful for grapegrowers to monitor the TSS of grapes during the ripening process and before harvest or delivery to the winery. Grapegrowers supplying grapes to wineries under contract can, in some cases, be required to add sulfur dioxide to the bins of grapes immediately after harvest and before transporting to the winery. In some relatively rare cases, it might be a contractual requirement that grapegrowers measure the concentration of SO2.
For a winery, knowledge of the TSS of grapes they receive is important and it may be appropriate to also measure the acidity of the grapes because this is a very important factor in spoilage prevention. Generally speaking, it is quite risky, though by no means impossible, to make sound wine without knowledge of the concentration of more grape compositional variables than just TSS, pH and titratable acidity. Therefore, if setting up your laboratory at this level, it is advisable to obtain contract analysis for the other compositional variables at higher levels as necessary.
Total soluble solids (TSS)
The measurement of total soluble solids in grapes or must is an indication of the sugar concentration. This is because sugar and water are the two components that together make up the greatest proportion by weight of grapes. This measurement is often used as a basis of payment for grapes.
The most commonly used scales of units for TSS are degrees Brix or Baumé. The scale of Brix is defined as the equivalent percentage of sucrose in water (i.e. g sucrose / 100 mL). The Baumé scale is, in fact, a salinity scale, but is often used in the wine industry for estimating the concentration of TSS because, by chance, it roughly approximates to the yield of alcohol that will result from the fermentation of the sugars (Iland et al. 2000; Rankine 1998).
Commonly used techniques for determination of TSS are:
- Hydrometry
- Refractometry
- Density meter
pH
The measurement of pH is considered to be one of the important analytical measurements in grapes and wine. This is because it gives a good indication of the degree of ripening in grapes, has a profound effect on the metabolism of microorganisms in wine, influences the flavour and colour of wine, and also has a major influence on the physical and, most importantly, microbiological stability of wine. The pH scale from 0 to 14 is logarithmic meaning that an increase of 1 pH unit represents a 10-fold increase in the concentration of hydrogen ions (Rankine 1998).
The commonly used technique for determination of pH is:
- Potentiometric (electrode)
Titratable acidity (TA)
Titratable acidity is a measure of the free and bound hydrogen ions from all acids that are present in the sample. The measurement of TA is a good indicator of the amount of acids present and is therefore sometimes used to monitor degree of ripeness of grapes. TA also has an effect on the sensory properties of wine and can also be important for monitoring maturation for any potential spoilage. The TA result is usually expressed as grams per litre equivalent of tartaric acid but can also be expressed in terms of other acids.
Commonly used techniques for determination of TA are:
- Titration to end point by colour indicator
- Titration to end point using pH meter
Sulfur dioxide
Sulfur dioxide (SO2) in must and wine acts as a chemical antioxidant and inhibitor of microbial activity, and is considered as a preservative. The amount of SO2 allowable in wine is regulated and it is therefore an important measure for quality control. Sulfur dioxide exists as two forms in wine – ‘free’ and ‘bound’ – which together make up the ‘total’ sulfur dioxide. Together with the measurement of alcohol, pH and residual sugar content in wine, the amount of SO2 can provide a more complete indication of the potential risk for spoilage to occur (see also Robinson and Godden 2003).
Commonly used techniques for determination of SO2 are:
- Aspiration / titration (Rankine and Pocock)
- Reaction / titration (Ripper)
Preliminary level
When wine is being produced in reasonable quantities, preservation and prevention of spoilage becomes more critical. The main variables that influence prevention of spoilage of wine are the alcohol content, the concentration of residual sugar, and the concentration of added sulfur dioxide (SO2), along with pH and TA, which have already been discussed above. Since alcohol content will not change markedly once fermentation is complete, and is only slightly affected by any spoilage, its use as a preventative indicator becomes limited once determined for a wine. If wine is to be bottled for retail sale, it is essential to know the alcohol content accurate to the extent as required by the relevant legislation (e.g. to within 0.5% alcohol content for the Australian retail market). For both of these reasons, sourcing contract analytical services for the determination of alcohol content might be an appropriate proposition.
Alcohol
Alcohol in wine is the product of the yeast fermentation of sugars that are present in the grapes. Whilst the alcohol content is important to the taste of wine, there are normally legislative requirements in most countries for the alcohol content to be stated on the label. The alcohol content can also give an indication of the potential risk for spoilage to occur, because the alcohol acts as an inhibitor of many wine spoilage microorganisms. The risk of spoilage generally decreases with increasing alcohol concentration.
Commonly used techniques for determination of alcohol are:
- Ebulliometry
- Distillation / hydrometry
- Distillation / densitometry
- Near infrared spectroscopy
- Gas chromatography (GC)
Sugar
The amount of sugar remaining in wine after fermentation is an important measure for quality control purposes. Measurement of the concentration of residual sugar is often used to ascertain the completeness of fermentation, or to confirm that the sugar content conforms to some legal or commercial requirement. The amount of residual sugar (i.e. glucose and fructose) in wine can give an indication of the potential risk for spoilage to occur. Residual sugar can be readily used as a substrate for the growth and fermentation of wine spoilage microoganisms and, in contrast to the effect of alcohol on the spoilage risk, presents an increased risk with increasing concentration.
Commonly used techniques for determination of residual sugar in wine are:
- Rapid method – test pills
- Reaction / titration
- Enzymatic assay
- High performance liquid chromatography (HPLC)
Volatile acidity
The volatile acidity (VA) of wine consists mainly of acetic acid, which is produced to some degree in all wines as a result of normal yeast and bacterial fermentation. The concentration of VA is often used as an indicator of the degree of spoilage and is, therefore, an important measure for quality control. The amount of volatile acidity allowed in wine for commercial sale is usually regulated by the relevant food laws and therefore is an important measure from a commercial point of view.
Commonly used techniques for determination of VA are:
- Steam distillation / titration
- Enzymatic assay
- High performance liquid chromatography (HPLC)
Density
Measurement of the density of wine is required for calculation of the extract content of wine. This measurement can be a useful parameter in quality control applications, for example, in parallel with measurements of alcohol, pH and TA to indicate possible dilution or contamination.
Commonly used techniques for determination of density in wine are:
- Hydrometry
- Density meter
Intermediate level
If significant quantities of wine are being made and bottled on-site, further tests are needed in order to make informed decisions about processing to ensure the stability of wine. Some wineries with their own bottling plants also provide contract-bottling services to other wineries and in these cases it is extremely important for the winery laboratory to have the capability for a broad range of analytical tests that are appropriate to objectively demonstrate that the bottling process has been conducted as required by the customer. Some medium and larger wineries also make payments for red grapes that are based partly on the concentration of total anthocyanins (‘colour’) of the grapes. The colour determination will require the use of a spectrophotometer – the equipment required for this assay is also useful for many other determinations (e.g. enzymatic assays, relative browning of white wines).
Total anthocyanins (colour) of red grapes
The measurement of the concentration of total anthocyanins (‘colour’) in red wine grapes (Iland et al. 1996) has found increasing use in the wine industry as an indicator of winegrape quality (Kennedy 2002). This is because it has been shown that, in certain well-defined situations, wine grape colour correlates with potential wine quality (Dambergs et al. 1999; Francis et al. 1998).
Commonly used techniques for determination of red grape colour are:
- Spectrophotometric
- Near infrared spectroscopy
Malic acid
Malic acid is often measured to follow the progress of malolactic fermentation in wines and to confirm when the fermentation is complete.
Commonly used techniques for determination of malic acid in wine are:
- Paper chromatography (qualitative)
- Thin layer chromatography (qualitative)
- Enzymatic
- High performance liquid chromatography (HPLC)
Stability – heat
Wine contains proteins, some of which can be susceptible to heat and have the potential to cause the formation of an unsightly haze in the wine. This is particularly undesirable in bottled wine and, therefore, most wineries ‘stabilise’ their wines prior to bottling by removing the heat-unstable proteins. There are a range of heat stability tests that are designed to estimate the possibility of the wine forming such a haze after exposure to heat. It should be remembered that these tests are only indicative and it is prudent for wineries to validate their own test criteria (i.e. for pass/fail) according to the degree of margin they wish to accept in their products.
Commonly used techniques for determination of heat stability of wine are:
- Heat test
- BentoTest
Stability – cold
Wines usually have the potential for crystals of potassium bitartrate to form out of solution over long storage periods and especially on exposure to cold or cool temperatures. Such deposits are unsightly and ususally considerd undesirable from the consumer’s point of view. Therefore, many wineries ‘stabilise’ their wines prior to bottling, by subjecting the wine to conditions conducive to accelerated precipitation of potassium bitartrate, that is, cooling and seeding with crystals. There are a range of cold stability tests that are designed to estimate the possibility of the wine ‘throwing’ such a deposit at some time after bottling. It should be remembered that these tests are only indicative and it is prudent for wineries to validate their own test criteria (i.e. for pass/fail) according to the degree of margin they wish to accept in their products.
Commonly used techniques for determination of cold stability of wine are:
- Refrigeration
- Freeze / thaw
- Conductivity (contact process)
- Concentration product
Other
At this level of operation, there are several other methods that might be of use and some of the more important ones are listed below. For details on the development and implementation of these analytical techniques, consult the references listed below or please contact the winemaking and extension services team during business hours on 08 8313 6600 or via e-mail.
- Stability – microbiological
- Filterability of wines
Advanced level
For those wineries that wish to ensure compliance with export regulations, as well as provide some troubleshooting support to winemaking operations, a range of analytical determinations requiring sophisticated laboratory techniques will be required. Such analysis methods include:
- Organic acids
- Cations
- Anions
- Agrochemicals
- Flavour or aroma compounds or indicators
- Trace elements
For details on the development and implementation of these analytical techniques, please contact the AWRI helpdesk on 08 8313 6600 or via e-mail.
References and further reading
- Bruer, B.A.; Bruer, D.R.G.; Brien, C.J. (1982) Shelf life of some common winery laboratory reagents. Amer. J. Enol. Vitic. 33: 159-163.
- Dambergs, B.; Kambouris, B.; Gishen, M.; Francis, L. (2000) Measuring fruit quality. Davies, C.; Dundon, C.; Hamilton, R. (eds) Modern viticulture – meeting market specifications: proceedings of seminar; 15 July 1999, Barossa Convention Centre, Tanunda; 25 August 1999, Cowra Civic Centre; 3 September 1999, Mildura Arts Centre, Mildura; 16 September, Technology Park Function Centre, Perth.
- Francis, I.L.; Iland, P.G.; Cynkar, W.U.; Kwiatkowski, M.; Williams, P.J.; Armstrong, H.; Botting, D.G.; Gawel, R.; Ryan, C. (1999) Assessing wine quality with the G-G assay. Blair, R.J.; Sas, A.N.; Hayes, P.F.; Hj, P.B. (eds) Proceedings of the tenth Australian wine industry technical conference; 2-5 August 1998, Sydney, NSW. Adelaide, South Australia. Australian Wine Industry Technical Conference Inc. 104-108.
- Howe, P. (1999) Spectrophotometric analyses in the winery laboratory. Vineyard Winery Manage. 25(6): 92-97.
- Iland, P.G.; Cynkar, W.U.; Francis, I.L.; Williams, P.J.; Coombe, B.G. (1996) Optimisation of methods for the determination of total and red-free glycosyl glucose in black grape berries of Vitis vinifera. Aust. J. Grape Wine Res. 2(3): 171-178.
- Iland, P.; Ewart, A.; Sitters, J.; Markides, A.; Bruer, N. (2000) Techniques for chemical analysis and quality monitoring during winemaking. Campbelltown, SA Patrick Iland Wine Promotions.
- Kennedy, A.M. (2002) An Australian case study: introduction of new quality measures and technologies in the viticultural industry. Blair, R.J.; Williams, P.J.; Hj, P.B. (eds). Proceedings of the eleventh Australian wine industry technical conference, 7-11 October 2001, Adelaide, South Australia. Adelaide, South Australia Australian Wine Industry Technical Conference, Inc. 199-205.
- Robinson, E M.C.R.; Godden, P.W. (2003) Revisiting sulfur dioxide use. Tech. Rev. (145) 7-11. The Australian Wine Research Institute, Adelaide SA.
- Rankine, B.C. Making good wine: a manual of winemaking practice for Australia and New Zealand. 1998. South Melbourne, Sun Books (Macmillan Australia).
- Yap, S.J. (1977) Microbiological tools for the winery laboratory. Aust. Grapegrower Winemaker (163): 8-10; Adelaide, SA: Ryan Publications.