We are wrapping up the summary of the 2017 Vintage report with the last session focussing on Phenolic extraction presented by Federico Casassa.
Overview of phenolic extraction into red wines: a cellular perspective
Continuing on the theme of fruit ripening and fruit maturity from our previous article, the Vintage Report’s next scientific guest, Federico Casassa, Professor of Enology/Sensory Analysis at Cal Poly San Luis Obispo, presented his most recent research on phenolic extraction.
Professor Casassa began with an overview of the grape skin cell wall composition and seed makeup, in order to differentiate the paths taken by skin and seed tannins when extracted from the berry. In order to share his recent research on matrix-derived interactions between tannin compounds, Professor Casassa shared an experimental fermentation with extended maceration on Merlot. At the beginning of the fermentation, skin and seed tannins were extracted in a relatively linear, 50:50 ratio, before reaching a plateau in tannin concentration.
However, as fermentation continued for another ten days, the tannin concentration once again began to increase in a linear fashion. The ratio between skin and seed tannin changed during this second increase in concentration, resulting in a final tannin ratio of 75% from seed to 25% from skin. This brings forward the question: what is happening to release this second wave of seed tannin? Are the seeds “collapsing”, or reacting to the higher alcohol content further into the fermentation?
Less is known about the seed tannin extraction than skin tannin, which are likely released from the inner layer of skin tissue and are exceptionally prone to fining during the winemaking process. In conclusion, many matrix interactions occur during crush and fermentation with highly reactive tannins and with the presence of anthocyanin. Further research will hopefully shed even more light on tannin extraction.