My dairy inspector discourages me from using a simple timer to indicate when pasteurization is done, he recommends we go by the vat chart recorder and allow three full 10minute hashmarks to pass. The problem is that he does not recognize the time at temperature that passes before the first 10minute marker is reached, as a result our pasteurizations can last 30minutes plus up to 9minutes that elapsed before the first 10minute start mark was hit. What effect could this have on the cheese? We do semilactic set soft cheeses.
I would give it a try and see how it goes. I suspect that you will have no problems. I don't know at what rate casein denatures at that temperature, but I'd be surprised if an extra 30% time had significant difference. Just to be clear, I would do it on small quantities first :-) Just jury rig a double boiler, take a litre of your raw milk, pasteurise it at 145F for 30 minutes, take another litre and pasteurise it at 145 for 40 minutes. Make your semilactic cheese (in small quantities) and do a blind taste test (have someone randomly lable 1 of them A and the other one B and record which is which somewhere -- then *you* taste them without knowing which is which). If you can't tell the difference, then you can go ahead and try it on a commercial batch. There might still be problems, but that should derisk it pretty thoroughly.