I thought I would post this to share my experience of this year's harvest, and also to hopefully start some discussion around the best way to go about pre-fermentation adjustments when brix comes in a bit (or a lot!) high. I have followed with interest @NorCal's thread on making petit syrah from high brix grapes, and I'm sure there are others out there with similar experiences.
This year I bought a 1/2 ton of pinot noir; it was a weird ripening year and, long story short, my grapes came in at 27.5 brix. pH was 3.59 and TA 0.64%, which seemed in an acceptable range given that (based on starting brix) I was heading towards making a 'bigger' style of pinot noir.
A note about sample preparation and measurement: for pre-fermentation measurements using a refractometer I took a scoop of grapes + juice and blenderized it before straining/filtering and measuring. (Centrifugation would have been ideal, but I didn't have access to a suitable sample centrifuge). I think this is particularly important in high brix/later-harvest samples; if there are dessicated/raisiny grapes, they are likely to have a substantial fraction of sugar bound up in them which will not register in a pure juice sample - more on this later.
Day 1: destemmed and added 30ppm SO2, left to cold soak for 2 days
Day 2: Brix = 27.5 (blenderized sample, refractometer)
Day 3: With a goal of 24.5 brix (14.7% potential alcohol) I figured I would want to add ~30L of water (with 6g/L tartaric acid to maintain pH level). Wanting to be conservative, I started out with 25L. After thorough mixing, and taking another blenderized/filtered sample, I had brix = 24.0 (by refractometer). Notably, brix from juice alone was just 22.5 at this stage (refractometer and hydrometer). I also submitted a sample for lab analysis of glucose-fructose, which should give a more accurate measure of fermentable sugars and hence potential alcohol. This came back as 258g/L, which is high; using the most widely accepted conversion factor of 16.8, it gives a whopping 15.3% alcohol (though the exact value depends on various things including yeast strain and could be higher or lower). I pitched my yeast today (but before I received the Glu-Fru lab results). I was worried about ending up with a stuck ferment since my yeast of choice (AMH) craps out above ~15%.
Day 4: Brix (juice alone) = 24.5 by hydrometer! Clearly grapes are still soaking up and releasing sugar into the juice. AMH yeast is known for having a long lag phase and while there were signs of bubbles, no overt fermentation. I decided to bump up the water again, adding another 12L with 6g/L tartaric. After thorough mixing, I measured 22.5 brix by hydrometer. Had I overdone it?
Day 5: Brix (juice alone) = 24.5 by hydrometer! Cap starting to form but still no temperature rise. I decided at this point to leave it alone and call my starting brix as 24.5
Day 6: Brix (juice alone) = 20.5. Temperature rising so we are off to the races. I'm hoping that, even if my potential alcohol is still a bit high, I will be able to reduce it by (a) having a high surface area in my primary fermenter (1/2 ton macro bin) and (b) frequent aeration (punching down 2x/day). Plus the bin is now outside and the weather is getting hot again, so I hope that will blow off some alcohol too.
This was quite the adventure and a learning experience for me. I'd be curious to hear how others have approached this sort of challenge, and I'll update on my final brix reading when my ferment is done, hopefully within the next 4-5 days.
This year I bought a 1/2 ton of pinot noir; it was a weird ripening year and, long story short, my grapes came in at 27.5 brix. pH was 3.59 and TA 0.64%, which seemed in an acceptable range given that (based on starting brix) I was heading towards making a 'bigger' style of pinot noir.
A note about sample preparation and measurement: for pre-fermentation measurements using a refractometer I took a scoop of grapes + juice and blenderized it before straining/filtering and measuring. (Centrifugation would have been ideal, but I didn't have access to a suitable sample centrifuge). I think this is particularly important in high brix/later-harvest samples; if there are dessicated/raisiny grapes, they are likely to have a substantial fraction of sugar bound up in them which will not register in a pure juice sample - more on this later.
Day 1: destemmed and added 30ppm SO2, left to cold soak for 2 days
Day 2: Brix = 27.5 (blenderized sample, refractometer)
Day 3: With a goal of 24.5 brix (14.7% potential alcohol) I figured I would want to add ~30L of water (with 6g/L tartaric acid to maintain pH level). Wanting to be conservative, I started out with 25L. After thorough mixing, and taking another blenderized/filtered sample, I had brix = 24.0 (by refractometer). Notably, brix from juice alone was just 22.5 at this stage (refractometer and hydrometer). I also submitted a sample for lab analysis of glucose-fructose, which should give a more accurate measure of fermentable sugars and hence potential alcohol. This came back as 258g/L, which is high; using the most widely accepted conversion factor of 16.8, it gives a whopping 15.3% alcohol (though the exact value depends on various things including yeast strain and could be higher or lower). I pitched my yeast today (but before I received the Glu-Fru lab results). I was worried about ending up with a stuck ferment since my yeast of choice (AMH) craps out above ~15%.
Day 4: Brix (juice alone) = 24.5 by hydrometer! Clearly grapes are still soaking up and releasing sugar into the juice. AMH yeast is known for having a long lag phase and while there were signs of bubbles, no overt fermentation. I decided to bump up the water again, adding another 12L with 6g/L tartaric. After thorough mixing, I measured 22.5 brix by hydrometer. Had I overdone it?
Day 5: Brix (juice alone) = 24.5 by hydrometer! Cap starting to form but still no temperature rise. I decided at this point to leave it alone and call my starting brix as 24.5
Day 6: Brix (juice alone) = 20.5. Temperature rising so we are off to the races. I'm hoping that, even if my potential alcohol is still a bit high, I will be able to reduce it by (a) having a high surface area in my primary fermenter (1/2 ton macro bin) and (b) frequent aeration (punching down 2x/day). Plus the bin is now outside and the weather is getting hot again, so I hope that will blow off some alcohol too.
This was quite the adventure and a learning experience for me. I'd be curious to hear how others have approached this sort of challenge, and I'll update on my final brix reading when my ferment is done, hopefully within the next 4-5 days.
