This year has presented us with a bit of a conundrum when we began to check on the Brix, pH and titratable acidity (TA) of our various grapes. We have always encountered high TA in our Chenin Blanc, but this year, we encountered high TA in our Cabernet Franc as well as our Cabernet Sauvignon. The puzzle was that the Brix were also high. In looking back at this year's growing season, we felt that we had good weather throughout the summer which would explain the high Brix, but what was puzzling was the high TA which never seemed to come down even though we let the grapes hang on the vines as long as possible.
Here are our numbers in the order in which the varieites were harvested:
| Variety |
Harvest Date |
Brix |
pH |
TA |
| Auxerrois |
September 23, 2019 |
19.6 |
3.26 |
7.35 g/L |
| Chardonnay |
September 28, 2019 |
21.5 |
3.17 |
9.4 g/L |
| Chenin Blanc |
October 14, 2019 |
21.6 |
3.15 |
13.5 g/L |
| Cabernet Franc |
October 26, 2019 |
23 |
3.32 |
11.3 g/L |
| Cabernet Sauvignon |
November 3, 2019 |
21 |
3.00 |
14.9 g/L |
Looking at the high titratable acids, we wanted to know more about the role of malic acid in grapes. There is a beautiful diagram that shows grape berry ripening and the changes in grape metabolites during ripening.
1
I used the above diagram in a previous blogpost called
Two Stages of Grape Berry Development, but in that blogpost, I focussed on the changes that occured in the grape berry in stage one and then in stage two.
In this and subsequent blogposts, I'm going to focus on the fate of malic acid in the ripening grape. Stay tuned!
Reference:
1. Moschou, Panagiotis & Aziz, Aziz & Roubelakis-Angelakis, Kalliopi, Chapter 7, Polyamines and grape berry development, The Biochemistry of the Grape Berry, (2012), 137-159.
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