Adjusting pH during AF in Syrah must

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Oct 19, 2021
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I'm very excited I found this forum, great stuff. I am completely new to wine (making, not drinking though ;).

(Small batch of Syrah low brix/SG, low end pH):

First time for me, got to a humble 100 kg of Syrah harvest (>10yo vineyard) 18 Brix, 3,2 pH and 1080 SG (crashed grapes must).

Allowed a 24h pre-AF maceration period at 18 Celsius (open fermenter - added 20 gr of Na Metabisulfite- I know, overdid it!)

Inoculated commercial yeast (Vitilevure Syrah YSEO).

Added 2,7 kg of sugar spread at 4 time points (1kg added right before yeast inoculation, and then 520gr q2d during AF- based on initial calculations to reach a 22,5 Brix target).

Fermentation nice & good 24h after inoc. and steady since (must always at 22 Celcius to try prevent yeast from over-stressing - low pH).

Problem (Gradually deceasing pH, very high TA):

pH gradually sunk
over the following days down to 2,9 on day 6 of AF! (for the first time tasted acidic, TA was 1,1%! first reading, I recently got the reagents).

Day 7 of AF I added 0,8 g/L of K+ Bicarb and pH reached 3,3 - TA down to 0,96%.

Day 8 (today) of AF pH back down to 3,2 (TA 0,98%) so I added an additional 0,4 g/L of K+ Bicarb. Will determine TA and pH again tomorrow.

Questions (a few...):

1) The rocky mistake with the 20 gr of Na Metabisulfite at the start, what should I do, check (analysis) to make sure its safe to drink?

2) I resisted to the idea of adding K+ bicarb initially, but acidic taste made me take action. Should I have waited until AF was done before adding K+ Bicarb, or even better, add Bicarb before AF to bring up pH up to...?

3) Should I inoculate ML bacteria after devatting, or should I wait and see (must analysis) if MLF starts? and how can I tell MLF is underway?

4) What and when to analyse (I'm on a budget, but want to learn, so hope to send some must to get some further "basic" info, suggestions?)

I'm very sorry for the long explanation, and will be very thankful for any comments or suggestions!

Cheers from Spain,


PS: sorry for my English, not my mother Language


Victim of the Invasion of the Avatar Snatchers
Sep 19, 2013
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near Milwaukee
Welcome to WMT!

You need to understand that fermentation produces CO2, which will reduce pH. But it is only temporary. Once the CO2 leaves, the pH will rebound to its previous level. Sooo...

1) Yes, your sulfite addition was on the high side, but it will be safe enough to drink. You added ~200 ppm. In the US, the legal limit is 350 ppm.
2) As discussed above, yes, you should have waited until after AF was finished to adjust pH.
3) It may be difficult to get MLF to work, given how much sulfite you have added. The only sure way to know if MLF is proceeding is to test for malic acid (usually by paper chromatography, although there are some other methods).
4) ¯\_(ツ)_/¯


Oct 19, 2021
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Hi sour_grapes,

Thank you very much for your great advice.

Some peace of mind regarding metabisulphyte thanks! A bummer that I've probably doomed precious ML bacteria though..

Back to pH... I am thinking I'm only allowing 15 minutes after sampling my must to setlle before making my measurements... To my surpise I read on other threads here yesterday that I may need to heat the must to get rid off the CO2 before measuring!

Will get hands on a paper chromatography kit to check for malic acid once AF is finished and retest at a later stage. I am considering sending a sample to a lab here (I'm at the Penedes region in Spain so have a few wine labs around...). I have a lactate meter myself, but for blood, with an analytical upper limit of 15 mmol/L (which I suspect may not be high enough for must though - need to investigate expected range of Lactic acid concentrations in must during AF and MLF).

I regret getting anxious w/ pH and not waiting until AF finished before manipulating pH... Beautiful learning experience though, and fantastic to get feedback from the saavy!

What I'm assuming here is that:

1) shouldn't add any more metabisulphyte in the steps ahead.

2) check for malic acid reduction and increase in lactic...

3) should I try to inoculatd ML bacteria?

I read some pelple inoculate ML bacteria during primary? I guess that, irrespective of when and how, high levels of SO in my must will tend to prevent these bacteria from thriving right?

TThanks again!

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