Trebbiano - bitter aftertaste, any ideas?

[InSadly]

Hi all, any ideas what may have gone wrong? September 2021 I bought 50kg (~£66?) of Trebbiano grapes from the local fruit importer. The end result is pretty good, but has an uncharacteristic, bitter after-taste (imagine the pith of the skin of an orange). I want to have another go this year, any ideas where this may have come from? I'll jot down the process to see if you can pick a hole in what I did wrong. (I made a similar quantity of Montepulciano Rosato at the same time, the only differences being: after treading, left 24hrs on skins before pressing and no addition of pectinaze - that turned out perfect, just like a comparator I bought from the Wine Soc).

50kg grapes in good condition
De-stemmed by hand (so little/no stalks in must)
Trod in a big plastic 'builder's' bucket I keep only for grapes (bare feet - so I doubt any pips got breached)
Pressed
Brix 18.5%, pH 3.54
27L must
60 drops pectinaze
2.5g K2O5S2
Leave 24hrs, rack off heavy sediment
+900g brewing sugar to aim for 12% ABV
Lalvin K1-V116 + 5 tsp tronozymol
+ 22 days fermentation ceased
2.5g K2O5S2
Cloudy - used Ritchies Kwik Clear 10ml A, pause, 10ml B
+ 10 days Still cloudy
Racked + 100ml bentonite slurry, whisked with drill attachment
+ 10 days, clear - racked & left in carboy with some spare in a DJ & plastic bottle, max 1" below bung
Over wintered in cold room (min 8° C)
Early Feb 22, racked off substantial tartrates (wine diamonds) (I do not filter)
33 bottles - noted a 'mineral' tang on top of the fruit
Summer 22 - good depth of fruit, true to type (cf Tesco £4.25 Vista Castelli Trebbiano D'abruzzo) but with unpleasant bitter aftertaste. No sign of oxygen contamination (no pong of acetone/nail-polish remover)

 

[The Baron]

Sounds like a tannin issue but I can not see any tannin additions in your recipe (usually Tea Bags for us homebrewers)

 

[jof]

But wouldn't he get enough tannin from the grape skins, as he made from whole grapes?

Or are you suggesting too much tannin?

 

[The Baron]

Yes I am suggesting there maybe too much tannin but apart from the the skins which if very thick may have given too much tannin to the wine I can not see anywhere else that tannin is introduced in the recipe.
You do get tannin from the seeds and stalks but as the OP has said he trod them by foot which should not have broken the seeds etc

 

[An Ankoù]

Did you wash the grapes first? Do you know if you grower uses any kind of spray before picking?
I understand that spraying with copper sulphate is quite common.

 

[InSadly]

Many thanks for the thoughtful replies.

I know bordeaux mixture is a common treatment which is CUSO4 & Ca(OH)2 (I use it on tomatoes), but I've never heard that it's a common step to wash grapes before de-stemming, does anybody else?

Tannins should be quite low, because I pressed the grapes immediately after treading. There were clearly tannins present, as after bulk cold conditioning a surprisingly hefty precipitation of wine diamonds was evident. Maybe I pressed the grapes too aggressively - I always try to get the last drop out - is that recognised as a common amateur faux-pas?

I see there are plenty of techniques to reduce tannin, Daniel Pambianchi (Techniques in home winemaking) lists several but he rather seems to indicate that high tannin in white wine is unusual. I could try on one batch and compare as I'll be doing 2 carboys of trebbiano this year (s.t. availability).

I'm about to order this year's batch of grapes, no idea what has happened to prices given the heat-wave, inflation & brexit. Has anyone else got a feel for this? I'm probably going for about 300kg if the price is reasonable, though I see the Wine Grape Club have said they aren't going to import anything this year (citing the importation obstacles as too onerous). Any thoughts on alternative suppliers would be most welcome.

 

[Bernie]

Hi all, any ideas what may have gone wrong? September 2021 I bought 50kg (~£66?) of Trebbiano grapes from the local fruit importer. The end result is pretty good, but has an uncharacteristic, bitter after-taste (imagine the pith of the skin of an orange). I want to have another go this year, any ideas where this may have come from? I'll jot down the process to see if you can pick a hole in what I did wrong. (I made a similar quantity of Montepulciano Rosato at the same time, the only differences being: after treading, left 24hrs on skins before pressing and no addition of pectinaze - that turned out perfect, just like a comparator I bought from the Wine Soc).

50kg grapes in good condition
De-stemmed by hand (so little/no stalks in must)
Trod in a big plastic 'builder's' bucket I keep only for grapes (bare feet - so I doubt any pips got breached)
Pressed
Brix 18.5%, pH 3.54
27L must
60 drops pectinaze
2.5g K2O5S2
Leave 24hrs, rack off heavy sediment
+900g brewing sugar to aim for 12% ABV
Lalvin K1-V116 + 5 tsp tronozymol
+ 22 days fermentation ceased
2.5g K2O5S2
Cloudy - used Ritchies Kwik Clear 10ml A, pause, 10ml B
+ 10 days Still cloudy
Racked + 100ml bentonite slurry, whisked with drill attachment
+ 10 days, clear - racked & left in carboy with some spare in a DJ & plastic bottle, max 1" below bung
Over wintered in cold room (min 8° C)
Early Feb 22, racked off substantial tartrates (wine diamonds) (I do not filter)
33 bottles - noted a 'mineral' tang on top of the fruit
Summer 22 - good depth of fruit, true to type (cf Tesco £4.25 Vista Castelli Trebbiano D'abruzzo) but with unpleasant bitter aftertaste. No sign of oxygen contamination (no pong of acetone/nail-polish remover)

How bitter is bitter? A bitter aftertaste isn't usual for Trebbiano but is a desired characteristic of some wines such as Verdicchio or Ortrugo.

 

[Stevieboy]

It's unlikely to be a Tannin issue - the grapes were pressed quickly and the there was no contact time for the skins (if I'm reading the method right), no stems, no pips broken.

You do mention a heavy tartrate sediment - there could be higher than normal residual tartric acid in the final product?

The other issue is of course that while you have ordered grapes, it is unlikely that those grapes came from a DOCG vineyard........

 

[InSadly]

How bitter is bitter? A bitter aftertaste isn't usual for Trebbiano but is a desired characteristic of some wines such as Verdicchio or Ortrugo.

I know we wine aficionados are meant to have an encyclopaedic vocabulary, but 'how bitter?' is testing my limits. I'd say 'not huge' but just aware that it shouldn't be there (and it put Mrs InSadly off the whole brew - but she favours acidic NZ Sauv Bl). I think the right note is the idea of chewing a bit of orange peel pith - not poisonous, but just out of place.

 

[InSadly]

It's unlikely to be a Tannin issue - the grapes were pressed quickly and the there was no contact time for the skins (if I'm reading the method right), no stems, no pips broken.

You do mention a heavy tartrate sediment - there could be higher than normal residual tartric acid in the final product?

The other issue is of course that while you have ordered grapes, it is unlikely that those grapes came from a DOCG vineyard........

Thanks for your thoughts. You've helped a lot. I have only been making wine from grapes for 10-12 years and until I read your message I thought tannin and tartrates were the same (duh!) so now I've googled and learnt (for shame) that they aren't. 'Tart' - that's the key, isn't it? The bitterness is a 'tart' aftertaste. I shall look up how to reduce tartaric acid.

As for DOCG, I don't know. Here's a picture of the supplier - not sure where they would indicate DOCG status:

 

[InSadly]

 

[Bernie]

Thanks for your thoughts. You've helped a lot. I have only been making wine from grapes for 10-12 years and until I read your message I thought tannin and tartrates were the same (duh!) so now I've googled and learnt (for shame) that they aren't. 'Tart' - that's the key, isn't it? The bitterness is a 'tart' aftertaste. I shall look up how to reduce tartaric acid.

As for DOCG, I don't know. Here's a picture of the supplier - not sure where they would indicate DOCG status:

Tartaric acid will give a wine a tart or acidic taste rather than bitterness.
Tannins make astringency rather than bitterness, though white wines tend to be less astringent.