Ice cider - fermentation won't start, extreme acidity reported

Question

I'm making a batch of ice cider, from apples from my own trees (not shop-bought juice). No preservatives. The constituent apples are early this year, and most of this batch is windfalls; 55% green and 45% red. These have been frozen in a chest freezer, and then shredded and pressed. The batch is ~21 litres, primary in a plastic bucket.

The freshly pressed juice tastes great, not too sour at all (back to this later).

I added campden tablets at pressing, in the recommended quantity, to mitigate browning of the juice and kill natural yeast. I waited 48 hours after the campden before proceeding.

I added pectolase and DaP nutrient in the recommended amounts.

I rehydrated and pitched the yeast, Lalvin D47, as per instructions. The yeast looked happy prior to pitching.

At this point, the Brix reading was 10.2 (1.04 SG). However, 36 hours later, there was no sign of fermentation - no airlock bubbles, which I know can be normal in a large bucket, but also no drop in SG reading or any visual sign of activity. I assumed that it could have been because my yeast had been stored out of the fridge for a long while, so I made up a new batch of yeast, pitched it, etc. Now another 24 hours has passed, and again no sign of activity of any sort, and again the SG is unchanged.

Temperature should be okay, around 18C to 20C.

I checked the pH with an inexpensive Chinese digital meter, and to my surprise, it read 1.86 - incredibly low. Although Lalvin don't give acidity specs, I understand that yeast generally are only viable from 2.0 up. It is possible that this cheap meter is reading inaccurately, so I'm waiting for more precise litmus strips to arrive, and also some calibration solutions so I can attempt to recalibrate it - so I can't confirm this reading is accurate.

I understand that freezing the apples in ice cider releases more sugars but also can make the result more acidic. Is it possible that this reading of 1.86pH is correct, in this situation? Does this sound realistic? If so should I attempt to correct the acidity first before trying to pitch again? I have potassium & calcium carbonate with which to do it, but I'm reticent to try to adjust pH if it turns out the meter I'm using is miles off the mark.

Is it worth trying to proof more yeast in this same juice, or do I just risk wasting it if the acidity is really the issue? Is there anything else I could have missed that may be the problem?

To summarise:

• Juice from own frozen apples, no preservatives
• Campden used but given plenty of time after
• Nutrient added (DaP)
• Pectolase added
• Yeast hydrated and pitched correctly
• SG seems reasonable to start fermentation
• pH reading extremely low, but may be incorrect
• No activity on airlock, no krausen, no drop in SG, 24 hours after second pitch attempt

Answer 1

I now have fermentation - TL;DR: do not trust cheap digital instruments!

The cheap Chinese pH meter I used was reporting nonsense, it turns out the juice was actually at 3.6pH (once tested with decent quality strips). So, nothing wrong with the acidity at all.

I tried again with properly rehydrated Lalvin D47 from another supplier, and now have good fermentation progressing with a lot of bubbling from the airlock.

It's possible the first two packets of yeast I tried were bad. The only other thing I can think of that I did differently, was that I took longer to carefully lower the temperature to 22C (temperature of the wort) from the rehydration temperature of 35C. It's possible I didn't do this slowly enough with my first two attempts.

So, in summary: acid had nothing to do with it, false alarm! The yeast was the problem after all.