Josh-- See also
Cooking by Hand. There is only a small section on curing but it's good and the whole book is worth perusal.
Phil-- C. bot in its vegetative and spore states are not generally harmful (except in infants); it is the toxin that's the issue, as you note. This toxin is a potent neurotoxin and the progression from infection to severe illness or death is nothing short of horrifying as the toxin attacts the face and eyes (usually) first before attacking lung control and making breathing difficult or impossible.
The Ph requirememt for C. bot growth inhibition is <4.6. Pressure canning raises the interior temp to 250F. There is some evidence that C. bot spores don't follow first-order kinetics which means that some spores might be more heat-resistant than others. The toxin, however, is heat-labile and can be destroyed at 176F for 10 minutes.
Usually we say the spore has to be activated by heat, so it takes cooking to greater than 130F, even 180F, to activate the spore. The spore does nothing as long as the food temp is above 125F. At below 122-125, the activated spore begins to germinate and turn into a vegetative cell. It is a time and temp relation but at 105F the time is about 2 hours. At 120F it is slow, 115F faster, and 105-100F fastest, and then it starts to slow down. Growth for C. botulinum and C. perfringens stops at 50F and 39.3F respectively. Of course the food nutrients affect this so there is no one time I can give you. We use perfringens as the worst case most of the time--the top end of the danger zone is based on C. perf. as it's the only bacteria in the group we are most concerned with that survive to higher temps, in its case temps of ~128.
Other than acid, salt is a great inhibitor and is the primary inhibitor in no-nitrate country hams, it prevents germination but the concern is mostly other pathogens and spoilage bacteria--but the salt concentration
must be high enough. Nitrites are preventives/inhibitors of C. bot. outgrowth. (I'm trying to get better specifics for you, Phil, on how/why this occurs. ... This just in from Carl Custer, a former microbiologist with FSIS: 'Nitrites inhibit the outgrowth stage of sporeformers. They can stimulate germination but then hang up the bug in the vunerable "outgrowth" stage.
Salt and pH act synergisticaly in the nitrite inhibitory effect.'
He also pointed me to a set of research papers by Terry Roberts and Angelia Gibson that I will search for. I do have some technical commentary from a researcher in Cali--email me if interested.)
C. bot. poisoning is very rare (~30 cases/year in the US) and is most often attributed to improperly home-canned foods. C. bot. is generally not a concern with raw meats (C. perf. is) but can be with several vegs, especially root vegs, that might well be used in sausages or as parts of cures, and hence the use of salt and nitrite/nitrate for curing and for many items that will be cold-smoked irrespective of risk potential as cold-smoking sets up very favorable conditions for growth.
Curing under refrigeration is the norm for the vast majority of products that will be cooked (via hot-smoking or not) or cold-smoked. (I do not cure some bacons with nitrite in the mix but all bacons I cure are cured cold, hot-smoked, chilled quickly, the cooked for service. No chance for outgrowth.) Curing under refrigeration is also the norm for products that will be air-dryed. Some of these cures contain nitrite (mostly for flavor/color) if the cut is intact and some do not. Spores cannot be inside the muscle of an intact cut and the constant exposure of the surface to oxygen prevents growth as the bacteria are anaerobic. (This is also the case with large intact cuts like hams that are not refrigerated during curing but left in, often, no-nitrate salt cures for months.)
For sausages that are not going to be cooked--those that are dry-cured for weeks--both nitite and nitrate are used in the mix to prevent botulism. To reduce the risk of spoilage over the long drying time the refrigeration stage is replaced by a incubation stage. When the sausage is first mixed a starter culture of beneficial bacteria is added. Incubation takes place over a period of 1-2 days at ~85F with high humidity. This period is obviously prime for bacterial growth and that is why starter culture is used. Though the nitrite/nitrate will handle C. bot. the added culture grows and helps to prevent spoilage by both 'taking over' the meat (providing competition for spoilage organisms) and by creating lactic acid which lowers the Ph further helping to prevent spoilage/bacterial growth. The long drying time lowers the water content of the product further preventing spoilage and when drying is complete the sausage need not be refrigerated.
I do not have the book in front of me but I do not recall the authors deviating from this at all.
Obviously there are key things to remember but the most important is to follow recipes precisely. This is especially important in regards to quantity of salt to meat and quantity of curing salt(s) to meat. One does not want to deviate here and it is best to weigh
everything for accuracy. Recipes for large amounts of sausage can be safely re-wriiten for other quantities but do the math accurately, check your work, then use a good scale. Of course, follow sound safe food-handling guidelines.
And one need not make dry-cured sausages nor do anything cold-smoked if one isn't comfortable. It's possible to enjoy the fruits of curing and charcuterie just as well by sticking with making pastrami, bacon (of various types and flavors), and fresh and hot-smoked sausages. For most of these items curing salt is more for color and flavor if it is used at all. Safe handling practices (cleanliness, cold) during prep and during and after cooking (food cooked to proper internals, cleanliness, food cooled quickly and stored properly) means there is little need for concern.
Hope this helps.