So to summarise my findings:
Cardosin A - extracted from dried flowers of Cynara cardunculus
Cardosin B - extracted from dried flowers of Cynara cardunculus
Chymosin - extracted from the abomasa (fourth stomach) of sucking-calves (calf rennet)
Pepsin - extracted from the abomasa (fourth stomach) of sucking-calves (calf rennet)
Apparently most commercial rennet is about 95% Chymosin and 5% Pepsin. Junket rennet however is 80% Pepsin.
There’s a fascinating white paper here: http://repositorio.ucp.pt/bitstream/10400.14/3582/3/Comparative%20studies%20on%20the%20gelling%20properties%20of%20cardosins%20extracted.pdf
Which indicates that the dried flower’s Cardosin A & B give clotting strengths of 1160 and 7556 IMCU/g whilst the Chymosin gives 174,000 IMCU/g. Thus the Thistle rennet is orders of magnitude weaker as mentioned by Sailor.
Lower pH (6.2 to 6.4 - by adding CaCl) gave better results than higher (6.6pH) but the performance of Chymosin suffered more than that of the Cardosins. Hence Linuxboy’s suggestion of a lower pH?
So to follow Linuxboy’s advice is it sufficient for me to lower the pH with CaCl or should I use citric acid or similar? Also should I buy Junket rennet for the Pepsin or is there a better alternative please?
Thanks in advance for the help and advice. Cheers, GD.