Ok we are talking about something that is a little outside my area of expertise, haven't made cider for years and just working from memory so might be a bit off track, but to the best of my recollection...
Campden tablets were developed to give people (not just beer/wine/mead/cider) makers a convenient way to add controlled amounts of metabisulfite, or more accurately free Sulphur Dioxide (SO2).
Being developed in the UK they were standardised to yield 50ppm of free SO2 in 1 Imperial Gallon (~4.55L).
Wine (and cider) yeasts are breed to tolerate 50ppm of SO2, wild yeast and bacteria don't like any SO2 and are inhibited.
You have added (from above 20 tablets to 48L) about double this amount, I suspect you may have inhibited your yeast to some extent.
On the waiting 24 Hours, from what I recall that was a stand for Pectinase enzyme (if used) to work on pulp and haze forming pectin's, it isn't required if the must is reasonably clear or you haven't used pectinase.
I just think you may have OD on the Campden.
I think next time I will only put in 1 Tablet per 5 Litres
1 Imperial Gallon is equilivant to 4.55 litres. So 48 litres = 10.5 Imperial Gallons so 2 tablets per gallon (PH 3.4 to 3.6) = 21 Tablets
Put in 20 Tablets.
On a lighter note
A quote from Edgar Allan Poe
“Believe nothing you hear, and only one half that you see.” LOL
This is quote from a Craft Cider Making Book by Andrew Lea
"Do I need to add campden tablets?"
(sodium metabisulphite) are sometimes added to apple juice before fermentation to subdue some of the wild yeasts and bacteria present in the juice, reducing the likelihood of the cider spoiling. Dosage depends on the acidity of the juice: a low acid juice (pH of 3.7 to 3.8) will require 3 campden tablets
per gallon of juice; average acid juice (pH of 3.4 to 3.6) will require 2 tablets per gallon; high acid juice (pH below 3) does not require campden tablets
To add campden tablets
, crush them in a little warm juice or water and add to the juice in the fermenter
. After 24 hours add a cultured cider yeast
or a cultured wine yeast
, and prime the airlock.
"Why can't I add yeast at the same time as my campden tablets?"
Andrew Lea, author of Craft Cider Making,
explains that adding Campden tablets
at the same time as the yeast
is likely to inhibit the yeast 'too strongly' and so will adversely affect fermentation. Adding the Campden tablets
to the juice at least 24 hours before the yeast
not only gives the Campden tablets sufficient time to kill off spoilage organisms, it allows time for the free sulphur dioxide to disappear before the yeast
is added so as not to inhibit the yeast."