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Classic Lloyd

pH levels during fermentation

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I’m trying to get a sense on how I should be adjusting pH during my rum fermentations.  I currently add acid to a 4.6 pH and this ferments fine, but I’ve read of folks going lower and higher (presumably to encourage or discourage bacterial growth?)

How do you guys adjust your pH in your rum fermentations?

thanks!

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I add citric and calcium carbonate at the beginning to get more buffer, then adjust mid run with cc.  I start about 5.2 and adjust if it drops below 4.0.  

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5.4 and citric to lower to 4.9 here...  which seems counter-intuitive, but works great.  Wheras not 'shocking' the pH downward will result in a stuck fermentation with a pH in the mid 3's in a few days

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I’m also wondering about pH on my 100% mollases wash. My pH came in at 5.74, but would love to be somewhere around 5.2-5.4. I am wanting to make a heavier and estery rum so not necessarily worried about staving off bacterial inoculation. Does anyone have a comparison in flavor profiles from using backset vs. lactic acid to lower their pH? Or is there no flavor difference?

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It seems like I've come across a fair number of anecdotal accounts that suggest that adding lactic acid does affect the end flavors - it being a fatty carboxylic acid and all, but it still seems like some folks are using it. That said, from what I've seen, most folks are using gypsum, citric acid, or sulfuric acid (or some combo of these) along with lime to control pH.

One learning since I posted this. The pH doesn't affect bacterial growth as much as it does yeast growth.  The range you're in encourages a fast, clean fermentation. Lower pH's will ferment slower but seem to produce more flavors (for a number of reasons).

Also, it takes a number of generations for your backset to become very acidic (well, actually just one really acidic batch).  Think about it as a chemical environment that resembles what you're going to ferment in.  Carrying batch to batch helps keep consistency there.  

So, I would definitely think about an acid additive.

Edited by Classic Lloyd
WHOOPS

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Lactic acid is definitely not a fatty acid. That being said it does have a lower sensory threshold so most people don't bother with it. I personally use phosphoric acid for pH adjustments but citric is also common. If you're looking for a heavy, flavorful rum, most people will agree that recycling dunder is the best approach.

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On 2/23/2019 at 8:04 PM, Classic Lloyd said:

It seems like I've come across a fair number of anecdotal accounts that suggest that adding lactic acid does affect the end flavors - it being a fatty carboxylic acid and all, but it still seems like some folks are using it. That said, from what I've seen, most folks are using gypsum, citric acid, or sulfuric acid (or some combo of these) along with lime to control pH.

One learning since I posted this. The pH doesn't affect bacterial growth as much as it does yeast growth.  The range you're in encourages a fast, clean fermentation. Lower pH's will ferment slower but seem to produce more flavors (for a number of reasons).

Also, it takes a number of generations for your backset to become very acidic (well, actually just one really acidic batch).  Think about it as a chemical environment that resembles what you're going to ferment in.  Carrying batch to batch helps keep consistency there.  

So, I would definitely think about an acid additive.

It's a good insight that lactic acid (and other carboxylic acids) are prone to esterification and so will most certainly affect the flavor of distillates. In rum, this is not always a bad thing. In fact, it's one of the reasons dunder and backset are often used - to coax greater esterification of bacterially produced carboxylic acids. 

 

Our experience is that you CAN have too much of a good thing with this. Butyric acid in very small quantities results in a delicious pineapple note. Too much of it and the vomit smell will never dissipate. So the takeaway is to be careful about using carboxylic acids to adjust fermentation pH. 

All that being said, I typically do not adjust the pH of our fermentations. They usually start at around 5.0 and finish at 3.8. If it drops too fast, I will sometimes adjust up with calcium carbonate, but I have never needed to adjust the pH down. 

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