Alcohol content of finished wine, whole cluster vs de-stemmed

[John_Morris]

Jamie - Was the post-fermentation volume of wine the same in both tanks? If the stems were taking up sugar (or alcohol), you’d expect to see the volume reduced somewhat, I’d think.

[brigcampbell]

Jamie - Was the post-fermentation volume of wine the same in both tanks? If the stems were taking up sugar (or alcohol), you’d expect to see the volume reduced somewhat, I’d think.

Good thinking, maybe the stems are absorbing vs altering the process.

it’d be interesting to take 5 lbs of stems in a stocking and put them in the tank then remove the sack and weight it after.

[Drew_Goin]

Very cool anecdotal study. Thanks for sharing!

[Todd_Hamina]

You are just learning this now?

[Paul_Gordon]

Jamie

I agree with you that stems reduce temps of a ferment but I would expect a higher temp to lead to a lower alc - more alc blown off.
There must be another factor.

Paul

[Jamie_Kutch]

Todd,

Nope, knew it for years but never had the numbers. Sounds like you knew and if so, anything to add as to why?

[Sean_S_y_d_n_e_y]

Question: does the actual volume of wine change when it is fermented with stems? Is the juice-to-solids ratio lower as well in the whole cluster ferment?

[Jamie_Kutch]

David,

I am not sure how much stems weight. The starting sugars are the same in both the de-stemmed and whole cluster. The stems don’t contribute and gluc/fruc as you say. I am not sure if I believe that the stem pulls alcohol out of the fermentation by absorption or that the stems absorb some gluc/fruc, but that is something I have thought about before and once again, a possibility. with regards to the common thought that alcohol blows off, the challenge is that you don’t see alcohol blowing off from carbonic ferments when the tank is completely sealed. Alcohol levels are actually incredibly low from fermenting carbonically and of course once again with 100% stems. More questions once again than answers…

Stems are comprised of wood and water. I have thought early in my career in and around 2007 that stems leach out some of the water and using stems acts like “watering back” but I definitely no longer believe that to be true.

John, I am not sure if the post fermentation volume is or was the same in both tanks. We pressed each separate and it isn’t something I looked at. If done again, I will measure and see. That said, often de-stemmed fruit has a higher yield due to the berries breaking up easier while a whole cluster tank get’s pressed and the cap is often far more wet than a de-stemmed tank. You get far less juice from de-stemmed pressing as the berries have given up their juice during ferment vs. whole cluster where often there are clusters in the bottom of the tank that have yet even be broken.

[John_Morris]

Thanks.

I’m going to nominate this for the Hall of Fame thread. Fascinating stuff!

[Jamie_Kutch]

Thanks John. I don’t post much and this might be my first starting thread in several years for me so I appreciate it. I will try harder when something seems compelling to share.

[Tom_G_l_a_s_g_o_w]

Thanks John. I don’t post much and this might be my first starting thread in several years for me so I appreciate it. I will try harder when something seems compelling to share.

This was a good post. You have a job to do, you’re not a researcher at UC Davis.

[David_Wright]

Well OK, out of curiosity I weighed a small bunch of red seedless table grapes, then removed the stems. Total weight 67.5g, weight of stems 1.5g, or 2.2% of the total weight. I suppose that many wine grapes are smaller relative to the stems than these plump table grapes, but even so It seems unlikely that the stems could contribute enough water/liquid to the juice to dilute it much.

Might there be a substance in the stems that affects yeast metabolism? (Cf. salt retarding fermentation when making bread dough.)

[John_Morris]

Well OK, out of curiosity I weighed a small bunch of red seedless table grapes, then removed the stems. Total weight 67.5g, weight of stems 1.5g, or 2.2% of the total weight. I suppose that many wine grapes are smaller relative to the stems than these plump table grapes, but even so It seems unlikely that the stems could contribute enough water/liquid to the juice to dilute it much.

Might there be a substance in the stems that affects yeast metabolism? (Cf. salt retarding fermentation when making bread dough.)

To make them less efficient at converting sugar to alcohol but still capable of using up all the sugar? If the substance just slowed down the yeast, you’d expect more residual sugar at the end of fermentation.

[Nick_Christie]

Thanks John. I don’t post much and this might be my first starting thread in several years for me so I appreciate it. I will try harder when something seems compelling to share.

Applause for the Try Hard, Jamie . Lovely to absorb your thoughts. Particularly in such an eventful year. We are thinking of you.

[Andrew_Morris]

So the de-stemmed tank made 6.7% more alcohol that the whole-cluster tank. How much do the stems weigh? They are not contributing sugar, so the whole-cluster tank has less sugar (to be fermented into EtOH) from the outset.

It is possible that the stems are contributing water to the batch. It is also possible that they absorb a small amount of etoh which gets discarded.

[John_Morris]

So the de-stemmed tank made 6.7% more alcohol that the whole-cluster tank. How much do the stems weigh? They are not contributing sugar, so the whole-cluster tank has less sugar (to be fermented into EtOH) from the outset.

It is possible that the stems are contributing water to the batch. It is also possible that they absorb a small amount of etoh which gets discarded.

Jamie said above he’s convinced that’s not the explanation. And it’s hard to imagine they could contribute enough water to bring down the ABV by a full degree, isn’t it?

[David_Wright]

Well OK, out of curiosity I weighed a small bunch of red seedless table grapes, then removed the stems. Total weight 67.5g, weight of stems 1.5g, or 2.2% of the total weight. I suppose that many wine grapes are smaller relative to the stems than these plump table grapes, but even so It seems unlikely that the stems could contribute enough water/liquid to the juice to dilute it much.

Might there be a substance in the stems that affects yeast metabolism? (Cf. salt retarding fermentation when making bread dough.)

To make them less efficient at converting sugar to alcohol but still capable of using up all the sugar? If the substance just slowed down the yeast, you’d expect more residual sugar at the end of fermentation.

No, not simply retarding the conversion. In this case, the whole-cluster batch had lower alcohol, but also lower sugar concentration. (This batch also had a lot more malic acid.) There’s a lot going on in fermentation… various byproducts are formed, yada yada.

[David_Bu3ker]

Fascinating stuff. I love the Uber geeky tech info. Feeds my Engineering brain.

Now I am waiting for Adam Fritsch to show up and complain about residual sugar.

[John_Morris]

Well OK, out of curiosity I weighed a small bunch of red seedless table grapes, then removed the stems. Total weight 67.5g, weight of stems 1.5g, or 2.2% of the total weight. I suppose that many wine grapes are smaller relative to the stems than these plump table grapes, but even so It seems unlikely that the stems could contribute enough water/liquid to the juice to dilute it much.

Might there be a substance in the stems that affects yeast metabolism? (Cf. salt retarding fermentation when making bread dough.)

To make them less efficient at converting sugar to alcohol but still capable of using up all the sugar? If the substance just slowed down the yeast, you’d expect more residual sugar at the end of fermentation.

No, not simply retarding the conversion. In this case, the whole-cluster batch had lower alcohol, but also lower sugar concentration. (This batch also had a lot more malic acid.) There’s a lot going on in fermentation… various byproducts are formed, yada yada.

So you’re positing that the sugar went other than to alcohol? I’m not being sarcastic. Just curious how that would work.

[Brian_S_t_o_t_t_e_r]

Fascinating stuff. I love the Uber geeky tech info. Feeds my Engineering brain.

Now I am waiting for Adam Fritsch to show up and complain about residual sugar.

With the recent posts in the 2019 German riesling thread I’m surprised there’s been no comment