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Why 4 hrs

Discussion in 'Food Safety' started by ak1, Sep 8, 2010.

  1. ak1

    ak1 Master of the Pit OTBS Member

    I'm wondering,

    Why does the USDA guidelines state 4 hrs to go from 40 deg to 140 deg.

    I checked Health Canada, and all they say is to cook to safe temperature. So I called and was told that as long as the food gets to the safe temperature in a reasonable amount of time it will be fine.

    So I'm wondering? Is there a reason why USDA guidelines state 4 hrs?
  2. richoso1

    richoso1 Legendary Pitmaster OTBS Member SMF Premier Member

    Last edited: Sep 8, 2010
  3. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member

    Health Canada: "Safe Temp in a reasonable amount of time?"

    Now there's some accuracy for ya!

    Do the speed limit signs in Canada say, "Please Drive At Safe & Reasonable Speeds"?

    I would think may scientists have spent many hours with many meats, with many probes, at many temps, and came up with the  minimum temp & time to smoke cook meats, because of people like us, who want to make meat as good tasting as possible, but still safe to eat.

  4. princess

    princess Smoking Fanatic

    WAIT WAIT!!! I know this one!!  This is all that fermentation stuff I have been studying!!

    It has everything to do with microbiology and the rate at which bacteria multiply and are able to make spores that can be heat resistant!!  ::cheer::

    But.. I am at work and won't have time to REALLY reply to this until later. :)

    Super-nerd to the rescue!

  5. (searches for nerd spit proof cover to apply on ones self for later)[​IMG]
  6. erain

    erain Master of the Pit OTBS Member SMF Premier Member

    Super nerd has it right on, and as time passes the rate the nasties multiply get to a point where they become unmanagable hence the 4 hour  40-140 degree time/temp lines...
  7. Its simple, we in Canada are reasonable and don't realy try to push the envalope, in the US if they didn't put a specific time there are less than desiriable resturants that would try to push there luck.  not saying that there arn't in Canada also, just not as much.  and Canada, not being as driven to sue, there isn't as much push to have exact numbers that can protect al restuarant from lawsuits as well.

    the multiplication of bacterial isn't linier between 40 and 140, the 4 hour bacteria multiplication is based off a specific temp, and most bacteria only have a 30 degree growth range, so the 40 to 140 is obvoulsy covering several types of backteria with different prefered temps. 

  8. arnie

    arnie Smoking Fanatic

    Now you know
  9. ak1

    ak1 Master of the Pit OTBS Member

    Did it! Ended up talking to a real person, with minimal wait time.

    That's pretty well it. The issue isn't so much the bacteria, but the toxic byproducts they produce. The 4 hr rule minimizes the amount of those toxins that are produced. However I was told there is a bit of a leeway (15-20 mins). If you go much longer than 4 hrs to hit 140, then although the vast majority of the bacteria are killed, there could be an unhealthy amount of toxins still present.

    I know! I thought the same. But then again, the person I talked to didn't seem very knowledgeable. Digging through the website all I could find was that food should be in the danger zone for no more than 2 hrs. I realize that there are differences between USDA & Health Canada guidelines. That's why I keep trying to find the reasoning behind the rules.
    Last edited: Sep 8, 2010
  10. Bearcarver

    Bearcarver SMF Hall of Fame Pitmaster Group Lead OTBS Member

    I look at it this way, in this particular instance:

    A lot of much more knowledgable people than I study this stuff. They come up with safety guidelines. I go by their guide, because they know more about it than I do. I don't have the time, the resources, or the inclination to be able to dispute their findings.

    I warn others who don't know about those guidelines. They can then follow those rules or not follow them. If they tell others those rules are stupid, I dispute that, because I don't want people who know less than those who made the rules to confuse people into getting sick or dying.

    Simple as that,

    Last edited: Sep 8, 2010
  11. mballi3011

    mballi3011 Epic Pitmaster OTBS Member SMF Premier Member


    I'm with Rich on this one. He knows his poo poo.
    Last edited: Sep 8, 2010
  12. princess

    princess Smoking Fanatic

    I totally agree with you, Bearcarver. But I am also like a four year old whose favorite questions is WHY?!?  Not because I'm going to disparage it or try to push my limits of safety, but because I think Science is Cool and understanding how stuff works is key to ensuring success down the road. (and I am a total nerd...)

    So: bacteria 101

    It's all about optimal environment. Ther are only a few ways to STOP bacteria from growing:

    Raise the temperature

    Drop the pH

    Remove the moisture

    Do *any* of those three and you halt bacterial growth. (This is why vinegar never goes bad and why dried onions last forever.)  You would not want to hold meat at low temperatures for THE EXACT same reason you wouldn't eat potato salad that's been out on the counter all day.  If you hold any food at optimal temps (with moisture present and without an acidic environment) the pathogenic bacteria will swiftly outnumber the beneficial bacteria and make you VERY sick.  As was mentioned before, once those toxins are present, there is no way to remove them.

    Think of this: If I handed you a grey slimy piece of rotted meat, no amount of cooking is going to make it safe. :P

    At the middling temps that most of us prefer to smoke at, bacteria have a field day, multiplying faster than ever before. It's dark, warm, wet & meaty. This is why meat on a countertop rots faster than meat in your fridge, or meat in your freezer. At every five degrees above freezing, some bacteria multiply twice as fast as they did before.

    So for example, if Bacteria A doubles every 36 hours at 32 degrees, then it doubles every 16 hours at 37 degrees. it doubles every 8 hours at 42 degrees. Every 4 hours at 47 degrees. Every 2 hours at 52 degrees. Every hour at 57 degrees. Every 30 minutes at 62 degrees. Every 15 minutes at 67 degrees. Every 7.5 minutes at 73 degrees. Every 3.75 minutes at 78 degrees. Every 112 seconds at 83 degrees. Every minute at 88. Every 30 seconds at 93... You see where this is going? If you hold meat above 40 degrees and under 140, you are creating the perfect environment for pathogenic bacterial growth.. aka ROTTING.

    This is ALSO why operating rooms are so cold, why fermented beer was safer than drinking water in the Middle Ages, why yogurt lasts longer than milk, why pickles never seem to go bad as fast as raw cucumbers, why we brush sliced apples with lemon juice to keep them from turning brown, why high pressure canning works so darn well, why you should be SO DILIGENT about keeping your meat prep area CLEAN and ICY... So much comes back to this exact answer.

    It is all about controlling the BAD bacteria and encouraging the GOOD bacteria.

    Wanna hear some more geek? Ask away!! :)


    robert123 likes this.
  13. meateater

    meateater Legendary Pitmaster SMF Premier Member

    So 40* to 140* in 4 hours it is. [​IMG]
  14. Princess, that is my kind of answer. Everybody says I explain to much when they ask me why. I am like you, have to know why, why, why.

    Thanks for passing that along.
  15. bbally

    bbally Master of the Pit OTBS Member

    Bacteria mutliply very rapidly at temperatures between 40 F and 140 F.  The studies clearly show that dangerous levels of colony size can start to be a real problem after four hours of incubation time.

    Canada has a lower limit on food in the unsafe zone.  The third bullet point is directly from the Canadian Food Inspection site and their food safety manual.


    • Bacteria can grow in the danger zone between 4°C and 60°C (40°F to 140°F).
    • To prevent the growth of harmful bacteria, keep cold food cold. Store it at or below 4°C (40°F).
    • Do not keep food in the danger zone for longer than two hours. Foods that need to be refrigerated or frozen should be stored immediately after they are brought home from the grocery store.
    • Refrigeration at or below 4°C (40°F) slows down most bacterial growth, while freezing at or below -18°C (0°F) can stop bacteria growth completely. (But remember: refrigeration and freezing won't kill bacteria. Only proper cooking will do that!)
    • Plan ahead: thaw food in the refrigerator, where the food will stay at a safe, constant temperature of 4°C (40°F) or below.
    WHY? Disease-causing bacteria multiply quickly when food is kept at room temperature.

    Canadian Food Link
    Last edited: Sep 8, 2010
  16. pineywoods

    pineywoods SMF Hall of Fame Pitmaster Staff Member Administrator Group Lead OTBS Member OTBS Admin SMF Premier Member

    Actually they changed it to 41-135 in under 4 hours for punctured meat. But I gotta say 40-140 in under 4 is easier to remember

    Also remember there is the intact muscle rule and that only requires the outer 1/2" pass the 140 (maybe 135 now)  mark in under 4 hours
  17. princess

    princess Smoking Fanatic

    I don't know very many people that have thermometers carefully calibrated enough to truly feel confident in the difference between 40 and 41 degrees anyway, you know?  But then, I deal mostly with sausage, and WHOA do sausage makers increase the risk for contamination.

  18. one thing I found out while looking up info on bacteria, is that a bacteria will only grow in a controled 30 degree range either side of the optimum temp, most of the nasty natural occuring ones in meat have the mid point of that range at 98 degrees, so they will multiply anywhere from 68 degrees to 128 degrees.  problem is the main ones that realy nail our coffin lids are the ones that we introduce by handling the meat.  and they have different mid points so hence the wider operating range.   but most bacteria that is already present in meat will be a body temp one.

    take e-coli for example.  the one that is responcable for the 3rd largest numbers of sicknesses in food, will only grow in that 30 degree range around body temp, and cooking to an internal temp of 140 fot 1 hour ot 167 for 10 min will destroy the bacteria and the toxin.  also if it is in normal O2 levels it will not grow.  so on your counter it wont grow, but as soon as you put it into your smoker the enviorment is now O2 depleated and away it goes.  also wraped food on the counter is a good enviorment for this bacteria. 

  19. scarbelly

    scarbelly Epic Pitmaster OTBS Member

    Great thread and folks stepping up with well researched answers

    Thanks for all of you taking the time to do the research and answer with facts[​IMG]

  20. princess

    princess Smoking Fanatic

    Hi stircrazy. Wow, I'm a little intimidated... you've been a member for nearly a year and have 100's of posts. You have me at the disadvantage, as I am quite a rookie here.  But this stuff? *IS* my forte, and is part of why I joined this forum, so I wanted to speak up one last time.

    I don't know you personally, so please don't take what I am about to say that way, okay?  [​IMG]   I'm just concerned because I feel like a PART of what you are saying is a bit misleading. .

    The part I am most concerned with is that statement that "most bacteria that is already present in meat will be a body temp one."  I would like to see the data for that statement, as it is totally inconsistent with my (limited, admittedly) knowledge of microbiology. Optimal temps means growing at the fastest rate, outside of optimal just means SLOWER, it doesn't mean stop. I could also be totally misunderstanding you...

    e.coli is the least of my worries when compared to bacillus cereusB.cereus spores can live WAY longer and at higher temperatures than e.coli. B.cereus is THE LEADING CAUSE of food poisoning in the United States. The only reliable way to destroy b.cereus toxin is to hold the meat at 259°F for more than 90 minutes. So, as meat handlers, we need to do EVERYTHING we can to ensure that as little as possible of the odorless, tasteless toxin from this terribly resistant bacteria gets produced.

    https://edis.ifas.ufl.edu/pdffiles/FS/FS10300.pdf  is a great resource for this...

    At this point, I think it may be prudent for me to step away from this thread. I get pretty passionate about food safety and don't want to get so hopped up on this topic that I begin to forget my manners. I am still very new here, truly a guest in all y'alls house, and I don't want to over-geek my welcome. If anyone personally has questions about micro-biology and/or food illness, I encourage you to send me a PM.