Thanks to some inspiration from Martin Reyes MW, I'd like to dive into the effects of Botrytis.
Define the effects botrytis cinerea can have on wine quality and explain the measures a winery should carry out when both white and black grapes have extensive botrytis infection. (2013)
A twofer! One foot in the practical with knowledge of flavors, one foot in P2 with laccase management. Time to chat with people in cool climate regions! ;)
Martin has generously offered to share some of his notes. But I'm struggling to tag him in this post, help!
Sarah Bray Kelli White Martin Reyes MW
Gabriella Macari may have some insight on grey rot on red grapes grown on Long Island!
Or any Napa producers working in the 2011 vintage...
For reference. Semillon with Botrytis at La Tour Blanche October 2019
Hi all. Crickets in the thread this week!
Here’s my rough outline for this question. I’m short on examples so I could use some help! The examiners report says that red, white, and sparkling should be mentioned. Some of my paragraphs are certainly more sparse than others!
Botrytis cinerea is prevalent in growing regions with late season humidity. The conditions surrounding the grape infection greatly affect the style of rot - infection followed by dry conditions can result in dry “noble rot” while infection followed by wet conditions can result in the compound infection of “grey rot”. In all Botrytis infections, oxidative laccase enzymes are active and can cause severe browning in whites and loss of color and tannin in reds. But both noble and grey rots result in quality changes ranging from increased concentration and honeyed flavors in noble rot, through loss of varietal character, tannin and color in extensive grey rot infection.
Heavy hand sorting should be employed on both white and red fruit with extensive grey rot. This will minimize the amount of Botrytis and associated Acetobacter cultures that infect the must. Additions of 40 mg/L+ of sulfur dioxide will inhibit microbes associated with Botrytis including Acetobacter. However, it will not inhibit laccase activity and wines are still at risk for oxidation.
Equipment should be sanitized after use so that other lots are not infected.
Skin and air contact should be minimized in both white and red grapes and musts. For white grapes, this means whole cluster pressing if possible, and use of inert gasses including carbon dioxide - this will minimize juice to skin contact and will minimize browning oxidation via laccase. For red grapes, cold soak should be avoided as it gives rot cultures an opportunity to proliferate the must. Sulfur dioxide additions may be utilized and will help to inhibit botrytis associated bacteria including acetobacter. However, it will not minimize must oxidation, color, and tannin loss.
Many pre-fermentation additions can be utilized to minimize the impact of laccase and flavors derived from mold. In white musts, bentonite can bind to laccase protein for removal. Bentonite can be added in conjunction with pectinase for ease of clarification, or with carbon for additional flavor fining. Botrytis culture and laccase can both settle with heavy solids and white musts should be clean racked before fermentation.
Example: Dr Loosen in Mosel, DE utilizes carbon and pectinase during flotation clarification for removal of botrytis grey mold flavors.
Red musts can benefit from enological tannin additions which serve to bind laccase proteins, and offer binding materials for unstable anthocyanins for color retention and stability.
Quick inoculation with commercial yeast is recommended to initiate fermentation. Cultured Saccharomyces cerevisie will outcompete and suppress botrytis associated bacteria such as acetobacter which can contribute high levels of volatile acidity. Additionally, the carbon dioxide produced by fermentation will protect the wine from further oxidation by laccase.
After primary fermentation, wines should be immediately racked under inert gas with sulfur dioxide addition. Similarly to pre-fermentation, Botrytis culture and laccase can both settle with heavy solids and wines should be clean racked after fermentation. Inert gas should be used to avoid additional oxidation by laccase.
The measures above do not make considerations for the following.
In the event of extensive dry botrytis infection, intentionally botrytized wines are produced. In this case, fining for flavor removal is not recommended as it will also remove the characteristic flavors of the botrytized style. However, laccase is still a consideration and inert gas should be utilized to minimize oxidation and retain freshness.
Some wineries may not be equipped for whole cluster pressing on white grapes. For example, Milbrandt Brothers in Washington state is only equipped to receive machine picked fruit without stems.
Facilities with flash detante or thermovinification equipment have an additional tool to combat laccase in red wines. The 85°C heat in the process will denature laccase enzyme, kill all botrytis associated microbes, and extract a large amount of color and tannin.
I fell behind my schedule with the course days also this week in NY. I am still working to finish it up but here's the first half:
Botrytis cinerea is a fungal vine disease common globally in damp and humid climates. Botrytis has two faces depending on the exact weather conditions, grape ripeness level and cultivar each with contrasting impacts on wine quality. In its benevolent form, “noble rot”, where is strikes healthy, ripe, white grapes, it can concentrate and affect grape chemistry to create the world’s most storied sweet wines. However, in its malevolent form, “grey rot”, or botrytis bunch rot (BBR), it can prove disastrous. BBR can spread rapidly, breaking down berry skins and leaving the flesh open to oxidization, bacterial and further fungal infection. An “extensive” level of botrytis infection affects 20-40% of the fruit as opposed to a “devastating” infection above 40% that bears the risk of total crop loss. This discussion will focus on the effects an extensive botrytis infection has on wine quality and explain winery management measures for both white and black grapes given this occurrence.
Effects on wine quality
Botrytis can have varied effects on wine quality depending its form, noble or grey and the cultivars involved. In both guises, thin skinned, tightly bunched grape varieties are most susceptible to infection. Botrytis produces the powerful oxidation enzyme laccase, which is highly soluble and resistant to both sulfur dioxide (SO2) and ethanol and thus difficult to eliminate from affected musts and wines. Laccase reduces varietal expression and fruitfulness, browns pigments, turning white grapes golden and black grapes a muddy brown and in most cases introduces earthy, musty aromas. As a primary pathogen, botrytis damages grape skins and paves the way for secondary infections from bacteria, spoilage yeasts and other fungi which consume must sugars and nutrients and impair later alcoholic fermentation or produce sensory faults. Of major concern are the ethanol tolerant acetobacter, which when in an oxygen rich environment produces acetic acid and gluconobacter which produces gluconic acid. All these effects lower wine quality for black grapes and in many cases for white grapes. Botrytis infected fruit, common in Champagne, is a major challenge in sparkling wine production and can provide additional quality impact to sparkling wine. Research from the University of Reims has shown that grapes with 20% botrytis level had up to 60% lower foam height and stability depending on cultivar, with black grapes faring worst. However, in a special case when botrytis strikes ripe, mature, white grapes and its spread is checked by sunny, dry weather it can manifest as noble rot. Noble rot dehydrates the grapes concentrating sugars, and acids leading to a must ideal for sweet wine production. Further it diminishes the primary fruit aromas in favor of its signature marzipan, apricot, and honey notes, adds a rich, glycerol laden, mouth feel and golden hue to the final wine.