Bentonite is most probably one of the additives mostly used by wine cellars. As a fining agent it can facilitate the settling process during the clarification of grape juice and wine or it can be used for the protein stabilisation of wines. As result of lees losses it can however lead to considerable product losses and also contribute considerably to the solid waste volume of cellars.

The development of an effective, cheap alternative for bentonite has been researched intensively. Last year the use of the two enzymes, Aspergillopepsin I (A1) and Aspergillopepsin II (A2) was legalised in Australia and New Zealand. Both are proteolytic enzymes which can break down the proteins, causing turbidity in wine. Scientists investigated the use of proteolytic enzymes for this purpose for a long time, but due to the resilience of the proteins causing turbidity and the relatively low enzyme activity under normal winemaking conditions limited success was obtained until it was found that a combination of the two mentioned enzymes is active between 60 – 80°C. This is also the temperature zone where the proteins responsible for turbidity are susceptible for enzymatic breakdown. The two most important protein types responsible for wine turbidity are thaumatine-like proteins and chitinases. If A1 and A2 enzymes are added to grape juice before the onset of alcoholic fermentation and the juice is heated and kept at 70°C for 1 minute the proteins will be more susceptible to the breakdown by the enzymes. Although it is usually thought that heating of juice is detrimental it is not true for such a short period. Contrary to this belief it can instead lead to the liberation of certain flavour compounds. It can also have other advantages like the decrease of laccase activity, which can otherwise cause browning and the fermentation process can also be faster.

Bentoniet_mainimage

Fining agents.

 

In spite of the success which can be obtained with the A1 and A2 enzymes a few practical problems exist. Presently there is only one Japanese commercial supplier of the product named “Proctase”, which was originally developed as a digestive drug for human use, but as result of the potential use in the wine industry other suppliers may also become interested. The juice heating is also of paramount importance for the use of the enzymes, but wine cellars do not always have suitable equipment for the heating and the retention of the juice at a certain temperature. It is however possible to utilise mobile units for that purpose. A third problem is the lab test for protein stability. The so-called heat test where a wine sample is kept for 6 hours at 80°C and then compared with an untreated sample is used by most cellars. The heat test checks for the presence of all proteins corresponding with a bentonite fining which removes all proteins. However, not all proteins cause turbidity in wine. Wine treatment with the A1 and A2 enzymes removes only the potential turbidity forming proteins from wine and the heat test can consequently not be used for testing the treated wine. High pressure liquid chromatography is required to determine the concentration of selective proteins. Smaller cellars usually do not have such laboratory equipment. Australian researchers are investigating the development of an adjusted heat test or other methods.

A cost analysis was also done to compare the bentonite and enzyme treatment financially. Processing conditions, heating and cooling equipment, pumping equipment, enzyme and bentonite purchases and product losses were taken into account. In the case of Sauvignon blanc, Chardonnay and Riesling wines it was found that enzyme treatment is the most beneficial for wines with high protein concentrations. The analysis also indicated that the inline dosing of bentonite is cheaper than the enzyme treatment. This advantage can however only be utilised by bigger cellars seeing that expensive equipment is required for it.

Except for the A1 and A2 enzymes other enzymes and resins are also investigated for protein stabilisation, but none has been commercially investigated (Logan, 2015).

Reference

Logan, Sonya, 2015. Brilliant ideas for alternatives to bentonite – progress and payoffs. Wine & Viticulture Journal, March/April 2015: 33 – 38.

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