Astringent Flavor in old black raspberry, any preventative?

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Rice_Guy

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I have been making black raspberry wine with 100% juice for years. At one year post ferment, in contest it can be a blue ribbon or at wine maker magazine a silver medal. BUT,, Normally a year to year and a half after bottling off flavors dominate and the raspberry/ fresh fruit flavor is gone. With pandemic priorities 2020 wasn't bottled till two years age at which time astringent (sucks the moisture out of the roof of the mouth) flavor dominated. I couldn't remove the flavor with gelatin or egg white (pulling tanins out). , , , Well the freezer is up to ten kilos of black raspberry so I should start this years batch.

Any ideas on how to prevent age related astringency in raspberries?
I was reading Pembachi over the weekend and he was suggesting PVPP fining in the juice can manage red grape astringency,
,,, Any one with experience dealing with astringent flavor?
 
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Following this because my red raspberry started out astringent, improved a little with backsweetening but now is again showing off flavors.
 
I don't have a solution but thought I'd pass this on...

Doing research on the day lily for wine I found that they have no tannin (not a surprise), the yellow flowers have carotenoid pigments (better tasting IMO) and the red flowers have phytocyanin pigments which are bitter. Yellow day lilies really do taste better and sweeter.

Perhaps there's something similar in play with black raspberries.
 
I’m actually drinking a black raspberry from 2020 and found the same situation. I back sweetened with honey in the glass until the astringency was diminished and wow the flavor really came through. I’m not sure how this translates to the bottle in terms of doing so prior to bottling and then being sure to wait two years... or making a change in bulk and then bottle...
 
My first thought is to drink the wine younger. While this doesn't help your existing wines, it may be a way to handle future wines. How does the wine taste in blends?

Trying PVPP sounds good for the upcoming batch.
 
Notes from last night’s Vinters club;
* a Scott labs speaker a few years back “PVPP is the last resort treatment” it fixes problems when nothing else will do it. To me this sounded like try everything else first.
* gelatin sometimes will work on the finished wine. Last year I should have done a bench trial instead of following the label on the LD Carlson package.
* several members are in harvest mode so we will have wines to compare

Another thought; when collecting Mom’s hardware one of the carboys with a solid cap had twenty year old black raspberry in it which was very good. ? age will fix the flavor ?
 
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I found an interesting paper on astringency that you might enjoy, and then went down a rabbit hole of leads...

Pires, M. A., Pastrana, L. M., Fuciños, P., Abreu, C. S., & Oliveira, S. M. (2020). Sensorial Perception of Astringency: Oral Mechanisms and Current Analysis Methods. Foods (Basel, Switzerland), 9(8), 1124. https://doi.org/10.3390/foods9081124

Below is a chart from the paper that interprets sensations and associated reasons. It led me to think what options were available to either mask the sensation or reduce the reason (your initial question). I had used honey with my blackberry to mask it, but that may be a short term solution (no pun intended) to what I think you're getting at in actually reducing the reason for astringency or off flavors associated with time in raspberries.


1657805709296.png

The below paper really gets into the reactions causing the sensation of astringency, but it also discusses the health benefits of astringent fruit (antibacterial, antiviral, anti-inflammatory, antioxidant, anticarcinogenic, antiallergenic, hepatoprotective and vasodilating). The authors discuss that Tannins are the key factor determining the degree of astringency in fruits and that all astringency removal methods base on the reaction of acetaldehyde with soluble tannins forming an insoluble non-astringent compound.

He, M., Tian, H., Luo, X., Qi, X., & Chen, X. (2015). Molecular progress in research on fruit astringency. Molecules (Basel, Switzerland), 20(1), 1434–1451. Molecular Progress in Research on Fruit Astringency. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6272358/#B8-molecules-20-01434


I had to follow that link to the below paper, which uses CO2 treatment for 24 hours for complete removal of astringency at any maturity level. This was for persimmons, I don't know if it would work on raspberries.

Salvador, Alejandra & Arnal, L. & Martínez-Jávega, J.M.. (2010). Optimization of the duration of deastringency treatment depending on persimmon maturity. Acta Horticulturae. 858. 69-74. 10.17660/ActaHortic.2010.858.7.

Subsequently, a thesis paper on the 'Impact of pre-fermentation maceration techniques on yeast populations and color of Pinot noir wine' discussed that "Must freezing freezes the grapes, rupturing the cell walls and membranes, potentially releasing more tannins in to the wine. It has been shown that wines with frozen musts had 52% more tannin than the control wines (Sacchi et al., 2005)." https://ir.library.oregonstate.edu/downloads/ws859h514

FINALLY... LOL

I ended up at the Washington State University Extension site and the following guidance on fining, and the use of proteins for astringency. It discusses a variety of types, reactivities, charges, assessments, etc...

http://pubs.cahnrs.wsu.edu/publications/wp-content/uploads/sites/2/publications/em016.pdf

Thank you for joining me on this tour...
 

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