We have learned a lot about food preservation over the past 50-60 years. Some of the things that we've learned show that the ways our Moms and Grandmas did things really are not reliably safe. I know I would never can some things the way my Grandma did!
For those who say, "but my mom/grandma always did it that way and nobody ever got sick" - all I can say is sometimes you get lucky - or that the symptoms set in so long after ingesting something that a connection wasn't made. If you take a 6-shot revolver and put one cartridge into one chamber, give it a spin, snap it shut, cock the hammer, point the muzzle at your head and pull the trigger - you've got an about 83% chance of not blowing your brains out. Of course, the odds change statistically the more times you do it. The same goes for the consumption of foods that have not been processed in a way that has been proven to be safe.
Although botulism poisoning symptoms usually appear within 6-18 hours ... they can sometimes not show up for as long as 2 weeks.
Now, regarding the commercial production of garlic infused olive oil, or those jars of ready-to-use minced garlic in oil ... it's a combination of heat, time and pH. Basically, the oil must be adjusted to a pH of 4.6 or less for the total mass of oil and garlic - after mixing and placing in the jars it must processed under pressure to increase the temp to 245°-265° F (I don't remember the exact temp) and held there for a minimum of 10 minutes. As jennyema noted - the lower the temp the longer it takes. If I remember the site where I found the information from the USDA/CDC/FDA there were only two acceptable acidifying agents - which I don't remember.
Oh, and FYI keltin - Botulism toxin is colorless and odorless. What you were probably observing was spoilage ... and the odor also included rancidity, and that can be very nasty!
I can not in clear conscience endorse, support, or recomment any food preservation method that does not conform to modern approved standards and methods.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain