The idea that honey should be pasteurized is truly odd. Honey has been used for centuries to dress wounds because of its antibacterial properties, and yet some people want to pasteurize it as if it might cause disease. Honey virtually never goes bad because it provides an inhospitable environment for most pathogens, yet some people want it cleaner.
Clostridium botulinum is a very common soil-borne organism that doesn’t cause problems for humans unless it is allowed to grow and produce toxins. This happens occasionally in low-acid (medium to high pH) foods that are not properly processed. Clostridium botulinum favors anaerobic conditions with a pH of about 4.6 or greater, so it sometimes is found in home-canned jars of fish, beans, mushrooms, and low-acid tomatoes.
As it turns out, the spores of Clostridium botulinum can survive in honey, but they can’t germinate, grow, or produce toxin in the highly acidic and extremely hygroscopic environment of honey. The spores just stay in the spore form. If we eat them, they go through us just as they would if they were stuck on a carrot or potato. The spores are everywhere and not a threat to humans with two exceptions—infants and individuals with compromised immune systems.
Very young children, usually during the first few months of life, have an underdeveloped intestine that sometimes allows Clostridium botulinum spores to grow within the gut and produce toxins. The condition is quite rare, but it most frequently happens after the ingestion of honey. The infant digestive system matures early and within a few months, the spores will pass straight through a child just as they do in an adult. Although the vulnerable stage is short, to be on the safe side, it is recommended that parents wait until a child is at least one year old before feeding honey.
Some people believe that if the honey is pasteurized it will be safe to give to infants. Nothing could be further from the truth. Pasteurization does nothing to botulism spores. Nothing.
Both the actual Clostridium botulinum bacteria and the toxins it produces are easily destroyed by boiling for several minutes or by holding them at lower temperatures for longer times. The spores, on the other hand, are extremely resistant. Pressure cooking at 250° F (121° C) for three minutes will kill the spores, as will other combinations of temperature, pressure, time, and acidity. At standard pressures, it could take hours of boiling to kill them.
But honey is pasteurized at much lower temperatures. Most sources I found recommended heating the honey to 145° F (63° C) for 30 minutes. Some preferred 150° (65.5° C) for 30 minutes. One suggested that the temperature be brought to 170° F (77° C) momentarily. In this environment, Clostridium botulinum spores are going to take off their little t-shirts and luxuriate in the sauna-like conditions.
The only thing that pasteurization does to honey is destroy many of the nuanced flavors and aromas, as well as many of the phytochemicals, antioxidants, and nutrients. In other words pasteurization degrades the product yet provides no clear benefit.