What is Botrytis cinerea?

What is in a name? Botrytis cinerea is ignoble rot when it infects grapes resulting in bunch rot and grey mold, but under the right conditions, Botrytis cinerea can develop into noble rot capable of producing wines of immense sugar concentration. So what is Botrytis cinerea?^1,2

• Botrytis cinerea is a fungus
• The initial inoculum probably develops from overwintering mycelia which are strands of the living fungus that can survive on previously diseased tissues or from resting structures called sclerotia
• Grapevine flowers, immediately after capfall, and berries post veraison are particularly susceptible to botrytis infection.
• Infected flower parts located in the developing cluster may initiate fruit infection later during the season
• As the fruit reaches maturity, resistance to fungal growth declines and under moist conditions, new infections, incited by spores from external sources become important
• Botrytis relies on damaged tissue to begin an infection so any wounded green tissue is susceptible
• Grape varieties that produce thin-skinned, tightly packed bunches are prone to splitting and retain moisture, providing conditions that suit botrytis
• Botrytis susceptible varieties include Chardonnay, Chenin Blanc, Grenache, Muller Thurgau, Pinot Gris, Pinot Noir, Riesling, Sauvignon Blanc, Semillon, Traminer, and Sultana

Here is the lifecycle of Botrytis cinerea:¹

What are the conditions that can lead to noble rot?²

• Noble rot develops late in the season under conditions of fluctuating humidity, specifically humid nights followed by dry, sunny days which limits fungal growth
• Fall infection of Botrytis leads to the release of pectolytic enzymes that degrade the pectinaceous component of the cell wall leading to the dehydration of the grape under dry conditions
• This drying of the berry is crucial to the concentration of the juice
• Drying also limits secondary infection by bacteria and fungi including Penicillium, Aspergillus, and Mucor
• A distinctive feature of noble rotting is a loss in varietal aroma due to the destruction of terpenes that give these varieties their distinctive fragrance.

So, Botrytis cinerea, ignoble during the growing season producing bunch rot and grey mold, but noble under certain rare conditions which produces a desirable transformation into a dehyrated, highly concentrated grape enhancing it's quality.
References:
1. AWRI, Viti-Notes, Botrytis, 2010.
2. Ronald Jackson, Wine Science Third Edition, Elsevier, 2008, pg. 520- .

The Story of Our Wedding Bag Grapes

No matter how careful our harvesters are, there will always be some grapes that are left in the vineyard. We take advantage of this oversight, by putting wedding bags on these grapes. We think that the wedding bags are the key to getting the grapes to dehydrate and concentrate their sugars while providing safety from being the target of predators still looking for a sugar high.

As the leaves from the vines begin to fall, we are finding more grapes to bag. In the photo below, the bunch on the left was a bunch we found on November 10 and the bunch on the right was a bunch we found on November 21.

We have been making a late harvest Chenin Blanc since 2019 when we harvested the wedding bags on November 19, 2019. In 2020, we were not able to get to the wedding bags until December 11. Here is a photo of what the grapes looked like:

The 2020 late harvest Chenin Blanc yielded precious little liquid, but we did manage to ferment it and called the wine our version of The Most Expensive Wine, a Tokaji Essencia.
This year, we are carefully monitoring the transition of Chenin Blanc grape to botrytized raisin so that we don't go too far on the spectrum to raisin. Yesterday, while we were working in the vineyard, we gathered a few grapes and took the Brix measurement. Here is what we found:

2018 Braida Monte Bruna Barbera d'Asti

We are always on the lookout to try different Barbera wines because we also grow Barbera. Recently, my husband bought this 2018 Braida Monte Bruna. We liked it immediately. The wine was dark garnet in color and had notes of blackberries and boysenberries at the beginning which lingered until the finish of acidity at the back end.
I learned a little more about this Barbera at the Braida Website. Montebruna is a Barbera d’Asti DOCG made with 100% Barbera grapes grown in an estate-owned vineyard in Rochetta Tanaro. The must spends two weeks in temperature-controlled steel tanks where it ferments and is then transferred to large oak barrels to age for a year. My husband said he purchased this wine for about $32.00. Worth it!

Statistics for Our Varieties from 2019-2021

Since 2019, we have been taking our harvest to Jonathan Edwards Winery where Jon and his crew help us to press the grapes and turn the juice into wine. I thought that it would be interesting to compare the harvest date, weight, volume, Brix, and TA of the varieites that we grow in the vineyard. We also grow Barbera, but that variety is still maturing and we are making this wine in our basement.
Auxerrois

Auxerrois	Harvest Date	Weight/ Lbs	Volume of Juice/ Gallons	Brix	pH	TA
2019	September 23, 2019	636	50	19.6	3.23	7.35 g/L
2020	September 27, 2020	1670	133	19	3.07	7.5 g/L
2021	September 28, 2021	1638	130	18	3.25	7.2 g/L

Chenin Blanc

Chenin Blanc	Harvest Date	Weight/ Lbs	Volume of Juice/ Gallons	Brix	pH	TA
2019	October 14, 2019	3920	305	21.6	3.15	13.5 g/L
2020	October 11, 2020	8201	655	23.3	3.09	12.1 g/L
2021	October 17-18, 2021	6200	496	20.4	3.17	14.6 g/L

Chardonnay

Chardonnay	Harvest Date	Weight/ Lbs	Volume of Juice/ Gallons	Brix	pH	TA
2019	September 28, 2019	291	26	21.5	3.17	9.4 g/L
2020	September 24, 2020	1136	80	23.5	3.0	10 g/L
2021	October 3, 2020	2625	210	20.4	3.28	8.2 g/L

Cabernet Sauvignon

Cabernet Sauvignon	Harvest Date	Weight/ Lbs	Volume of Juice/ Gallons	Brix	pH	TA
2019	November 3, 2019	332	30	19	3.25	11.1 g/L
2020	October 22, 2020	888	80	22.4	3.08	10.7 g/L
2021	October 24, 2021	561	45	20.1	3.07	10.4 g/L

Cabernet Franc

Cabernet Franc	Harvest Date	Weight/ Lbs	Volume of Juice/ Gallons	Brix	pH	TA
2019	October 26, 2019	377	32	23	3.23	11.3 g/L
2020	October 22, 2020	872	80	23.3	3.27	11.3 g/L
2021	October 24, 2021	402	32	19.8	3.2	7.4 g/L

It's interesting to see if there are any trends developing. One thing that is clear is that 2020 was an outstanding year for ripening and it is reflected in the wines we made in 2020.