It may be difficult for me to talk about the role of botrytis mould, in winemaking without freaking you out, because initially you might need to get your head around the idea of drinking fungus. So, for the purpose of this article which is intended to encourage you to buy a dessert wine, let’s think of botrytis as belonging to the mushroom family or perhaps as playing a similar role as another mould, penicillium glaucum, which is used to make gorgonzola cheese. You may also, like me, be disinterested in sweet wine, however, keep reading because as I discovered, not all sweet wines are the same and some of them are hidden gems tucked away in the back of people’s cellars, waiting for a time to shine.

Many years ago, I helped a friend move house and was gifted, amongst other things, a small bottle of dessert wine. After dusting off the bottle, its vivid yellow colour was revealed and I imagined how far gone it was, thinking it looked like an overcooked wooded chardonnay. Nonetheless, I stored it in my wine cupboard for a few more years, until one rainy day a friend spotted my little stowaway and suggested it had the potential to be amazing, so I unenthusiastically opened it. My response was “just wow!”, noting that it wasn’t overly sweet, as I had expected, and that it presented with an incredible mouthfeel as well as being almost perfectly agreeable in its complexity and flavours. All these years later, I am still impressed by that little bottle of liquid gold, and so here I am, a dry wine enthusiast, espousing the virtues of aged dessert wines. 

In winemaking, botrytis cinerea is visible on grapes as a blue-grey film and its influence in the vineyard may, or may not, be a good thing. When present in desirable quantities, this remarkable fungal infection is sometimes referred to as “noble rot”. In the right conditions, botrytis leeches moisture from the grapes, producing complex and intense flavours such as apricot, orange peel and marmalade. The unique flavours that arise from botrytis are highly prized and thus it is an important component of some of the world’s most expensive wines, hence the noble nickname. Besides concentrating sugar in the juice, botrytis enhances the glycerol content, adding smooth and viscous qualities to wine, which is why botrytis wines are sometimes colloquially referred to as “a sticky”.

Too much botrytis in the must (fermenting grape juice), however, will slow the fermentation process and impact the wine’s clarity by inhibiting the precipitation of colloidal materials, such as tannins and proteins. The colour of wine may also be negatively impacted, due to the presence of laccase, a sulphur dioxide resistant enzyme derived from botrytis that causes phenols to oxidise. In the vineyard, if botrytis takes hold at the wrong stage of development such as when buds and berries are emerging when moisture and temperature levels are simultaneously high, whole bunches of grapes will rot on the vine, rendering the crop useless. Therefore, viticulturists must take care to manage the levels of this somewhat friendly fungus in their crops throughout the growing season. Maybe botrytis is a bit like a musty old aunty (who makes great desserts) who you welcome with open arms on Christmas and Boxing Day, but who wouldn’t be anywhere near as welcome if she arrived in November, or stayed on until New Year’s Eve. 

Climatic conditions play a big part in whether the presence of botrytis is a help or a hinderance in the vineyard. Ideally, if there is high humidity interspersed with cooler weather, the growth of botrytis will be shorter term, causing a moderate concentration of sugar in the fruit. However, botrytis will bloom and break through the skin of the berries, if the humidity extends for a week or longer, making the influence of botrytis too overpowering. In hot, dry vineyard areas of Australia, the microclimate is not naturally conducive to botrytis growth. However, some of the best results using botrytis have come from these regions where the technique of spraying botrytis spores onto the vines is employed. Typically botrytis spraying has a positive effect in these regions because of the subsequent dry conditions, however, this technique is not used in the Margaret River wine region because high late-season rainfall predisposes botrytis to overtake and break through the surface of the berries, turning the bunches to mush.

Other winemaking techniques to incorporate botrytis include applying spores to unaffected grapes after they are picked. The harvest is then climate-controlled to achieve the desired level of mould development, however, this considerably adds to the already high cost of producing sweet wines. Production of wine using grapes colonised by botrytis is more expensive because the yield lowered by as much as 75 per cent due to dehydration of the berries. In addition, numerous risks including high volatile acidity caused by acetic acid bacteria, give winemakers cause to pay extra attention while making wine with botrytis. 

In the Margaret River wine region, a popular style of wine that features botrytis is known as cane cut, named after the technique of cutting the fruiting canes and leaving them to hang while the sweetness and flavour of the berries concentrates. Cane cut wines can be made from many different varietals and is a labour of love for many winemakers. The resulting mini-sized bottles of joy are a delicious finale to special dinners or cheese platters and are likely to cellar very well. Securing a few of Margaret River’s ‘noble stickies’ is a great investment, either to drink now or save for a rainy day. 

At the time of writing, patrons on our Full Day Gourmet Wine & Dine Tour and our Half Day Gourmet Wine Tour can purchase a 2019 Cane Cut Viognier from Xanadu or a 2018 Cane Cut Semillon from Voyager Estate. Keep an eye out for a new release from Cape Grace as their 2019 Cane Cut Chenin Blanc is sold out.

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