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Controlling pH in Rum Fermentation

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I'm currently developing a process for rum fermentations. We've never done fermentations in the distillery before, so it's a learning expereince for all. The small scale fermentations are going well, however in the second generation the pH has dropped too far and has caused fermentation to slow. I've corrected this by testing on a small portion of the wash and then adding Calcium Hydroxide to bring the pH up. Starting gravity is fairly standard, about 1.08. I've used 20% fresh dunder by volume, and it's a mixture of blackstrap and white cane sugar. The first fermentation sans dunder finished at about 4pH with an FG of 1.012. The second fermentation dropped to under 3.5pH where it began to slow things down at about 1.030.

The point of these small scale experiments is to develop a repeatable process for scaling up. One of the things I want to do is fixed 3-generational batches. So the first fermentation never includes dunder, the subsequent fermentations each include 20%, then you start from scratch and combine the low wines. So you end up with several discrete 3-fermentation cycles. This should deal with over-concentration of the dunder and traceability concerns. As such, I want to come up with a SOP for pH adjustment. The way I see it, my options are:

  • On-the-fly pH correction using Calcium Hydroxide
  • Adding Calcium Carbonate, which I understand should keep the pH at about 5. This could be good but is a little high for my liking
  • Create a buffer solution, perhaps citric acid and sodium citrate that buffers to something like 4pH. Add the solution either at the start of fermentation or after 24 hours
  • Record and repeat the results of the 'on-the-fly' pH ajdustments and have the corrective additions as regualar fermentation additions to be added at a set point in the fermentation.

What are your thoughts on these approaches? What ones do people prefer?

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