Guava and PH change

[back2it]

4 ltr juice
3 ltr water
1.6 kg sugar
Nutriant 1 tsp
Pectolase ¾ tsp

Started 31 July, fermented at 17°c and racked into demijohn today (19 Aug, so 19 days).

Start SG: 1.090
Today’s SG: 0.994 (not yet finished)

Start PH: 4.1
Today’s PH: 3.0

I am surprised at the PH change. Is this normal?

Thank you
Ray...

 

[David Violante]

That does seem like quite a change, what yeast did you use? Was the initial pH the juice only? I’m not so familiar in fermenting guava so someone more experienced with it will have some better ideas. The only other thing I can think of is pH meter calibration.

 

[back2it]

Thank you David,

I used Mangrove jacks AW4
The initial reading was just before I added the yeast.
I don't calibrate the meter every time but I do check it against a 7.0 solution.

I'm just kinda surprised and I would like to figure out why, so if anyone has any suggestions or insights, I would be grateful.

Thanks
Ray...

 

[Raptor99]

pH is a logarithmic scale, so the change that you measured would indicate a 10x time increase in acidity. I don't think that any fermentation process could cause that.

Some possibilities:
* One or the other of your pH readings was wrong
* If you added any acid blend (not mentioned above), maybe it was not fully mixed when you measured the initial pH
* If you were fermenting an extremely acidic fruit, maybe the fruit had not fully broken down when you did the initial pH measurement, and later it released a lot of acid. How much fruit did you use? I don't know if your guava could have released that much acid, but it seems unlikely.

Because of the third reason, I usually add pectic enzyme and then let the must sit for 12-14 hours to allow the fruit to break down. Then I measure and adjust the SG and pH if necessary before adding the yeast.

 

[back2it]

I did add pectic ensyme but didn't wait before making the reading, maybe that's it, but I am really curious so I'm going to make another batch to see if I get a similar result. I will make double PH readings before and after pectic ensyme addition. I have to satisfy my own curiosity here

Thanks for your input.
Ray...

 

[David Violante]

According to the University of the West Indies, the pH of the Guava is between 3.0 and 4.0 and is comprised mostly of malic and citric acid.

The Journal of Food Science also includes lactic, ascorbic and galacturonic, but that in cultivated guavas lactic acid was less. They also indicate that purées are closer to the 3.0-3.2 range and wild guavas are in the 3.0-3.5 range.

I looked at Mangrove Jacks AW4 on a few sites and they don’t really say it changes pH as one of its characteristics.

Still don’t know, but maybe this is helpful. Is the pH of your water higher?

 

[Raptor99]

Still don’t know, but maybe this is helpful. Is the pH of your water higher?

@back2it I'm also wondering, how much fruit did you use? How much water did you add?

 

[back2it]

Water PH 7.1. I created exactly the same batch and the starting PH is 3.5. I will see what the end result is in a few weeks but at the moment, I am leaning towards an incorrect initial reading as there was no change in PH between before and after pectic enzyme addition.

I don’t think I will ever be 100% sure what happened but as this is something I enjoy drinking I'm going to try multiple permeations and see if I can recreate and solve over time. It's going to be a tough job drinking all those gallons, but I suppose it has to be done in the name of science, or research, or anything else I can think of