1. Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.

Immersion bacon curing - lab test results

Discussion in 'Food Safety' started by wade, Mar 10, 2015.

  1. wade

    wade Master of the Pit Group Lead OTBS Member SMF Premier Member

    The purpose of the testing

    This thread is a summary of several threads about the calculation of cure update when immersion curing. These previous threads can be reviewed in full in the following threads:




    There are several immersion curing methods that are regularly quoted on here that use similar methodology - but which use very different initial brine strengths. One of these methods uses a very high initial brine strength (in the range usually associated with injection/pump brining) and relies on a % pickup factor when calculating the final cure concentration in the bacon. The other method uses a relatively low brine strength and relies on an equilibrium of cure being reached between the brine and the meat to achieve the desired final cure concentration.

    Each of these brines is being promoted by forum members who are considered by others as being experienced in the process of curing, however as these methods use initial cure concentrations that are so very different from each other it is hard to see how both can achieve results that are within the USDA commercial guidelines for bacon. I have therefore tested both cure methods on two popular cuts of pork and have had the resulting bacon tested at UK government approved food testing laboratory.

    Brine #1

    The first of these curing brines and the applicable calculation is described in the "Prague Powder #1" thread. This uses a brine which is in the region of 10x the expected resulting residual cure strength - which is commonly used for the commercial production of injected/pumped bacon. The calculation then relies on a known %age of the cure in the brine being picked up by the meat whilst it in immersed in the brine. The UDSA Processing Inspectors Calculations Handbook  suggests that this %age is calculated by the increasing weight of the meat as it is immersed in the brine.

    Quote from page 22 of the "UDSA Processing Inspectors Calculations Handbook" :
    • "The first method assumes that the meat or poultry absorbs not more than the level of nitrite in the cover pickle. Hence, the calculation for nitrite is based on the green weight of the meat or poultry (as is the case with pumped products), but uses percent pick-up as the percent pump. The percent pick-up is the total amount of cover pickle absorbed by the meat or poultry. It is used in the calculation for immersion cured products in the same way percent pump is used in the (previous) calculation for pumped products."
    The calculation that it then applied to calculate the resulting Ppm (parts per million) in the bacon is as follows:

            lb nitrite × % pick-up × 1,000,000 = ppm

            lb pickle

    Although there are references to this method in the handbook there appears to be a lack of credible evidence that this actually produces a resulting Ppm in line with the calculation

    Brine #2

    This is an equilibrium brine that is used by Pops6927  and is based upon a lower concentration of a brine that his father used commercially over 20 years ago. This uses a brine strength which is approaching 1/10th the concentration of Brine #1, however, like Brine #1, there appears to be a lack available evidence to demonstrate the resulting residual cure using this method.

    Brine formulations  

    The calculations from the threads use the following conversions when calculating the metric equivalents

    1 US gallon = 3.78 litres
    1 Cup of sugar = 240 g
    1 Cup of salt = 273 g
    1 Tbs Cure#1 = 17 g
    Cure#1 = 6.25% Nitrite and 93.75% Sal

    In the original threads I was showing the cure in mg/Litre however below these have been converted to mg/Kg for the purposes of calculating Ppm

    Brine #1 - as discussed by DDF in the Prague Powder #1 thread
     Per 3.5 US GallonPer 5 Litres
    Cure #114 oz (397 g)150.04 g
    Brown Sugar2-5/8 cups (630 g)238.1 g
    Salt3/4 Cup (204 g)77.1 g
    Water5 Litres5 Kg

    Brine #1 has a starting Nitrite concentration of 9.38 g in 5..47 Kg of final brine = 1,716 mg per Kg = 1,716 Ppm

    Brine #2 - Pops Low Salt Brine
     Per US GallonPer 5 litres
    Cure #11 Tbs (17 g)22.49 g
    Brown Sugar1/2 Cup (120 g)158.7 g
    White Sugar1/2 Cup (120 g)158.7 g
    Salt1/2 Cup (136.5 g)180.6 g 
    Water5 litres5 Kg

    Brine #2 has a starting Nitrite concentration of 1.41 g in 5.52 Kg of final brine = 255 mg per Kg = 255 Ppm

    The method

    Whole pork belly and a whole Pork loin were each taken from a single pig (in order to minimise biological variation) and each of these were cut into joints of roughly 1 Kg each. Each of the brines were then tested using both belly and loin joints. One of each was immersed for 7 days and the other for 14 days. At the beginning of the trial a sample was taken from each of the pork cuts in order to measure any background Nitrite levels occurring naturally in the meat.


    Single 20 litre batches of each of the brines were prepared and thoroughly mixed until all of the salts were dissolved and the the solutions were totally clear. 5 litres of the appropriate cure was then put into the curing containers for each pork joint. Each pork joint was cured in its own curing container, which had a tight fitting lid. 

    Samples of each of the brines were then taken and frozen, ready for testing

    Each pork joint was then immersed in 5 Litres of brine which, in these containers, was "just enough to cover it"

    The containers were all then stored in the fridge whilst curing. Some of the containers are shown here.

    Each day the joints were moved in the brine and the brine was stirred.

    After 7 days one of the loins and bellies from each brine were removed from the fridge, rinsed and dried and then placed on a rack in the fridge for 5 days to allow any cure gradient to equalise. A sample of the brine was also frozen for testing. 

    After 5 days a meat sample was taken from the centre of each joint which was then frozen ready for testing.

    The brine after 7 days looked murky but there were no off smells detectable

    The same was done for the remaining joints after 14 days.

    After 14 days all of the brines were looking decidedly murky with a distinct sediment on the bottom of each container. The smell was slightly meaty but was not unpleasant 

    Experimental results
    Weight g
    Resting g
    Weight %
    Test Sample
    weight (g)
    #1Loin75 Litres02/02/201597709/02/201510456.96206
    #1Loin145 Litres02/02/2015109616/02/201511878.30194
    #1Belly75 Litres02/02/2015106109/02/2015117811.03238
    #1Belly145 Litres02/02/201599716/02/2015115015.35219
    #2Loin75 Litres02/02/201589609/02/20159566.70227
    #2Loin145 Litres02/02/201593016/02/201510007.53224
    #2Belly75 Litres02/02/2015108609/02/2015121712.06226
    #2Belly145 Litres02/02/2015102616/02/2015115912.96226

    Lab Test Results

    As there is a natural conversion between Nitrite and Nitrate in biological systems, as advised by the testing laboratories, Nitrite and Nitrate were measured in each of the samples order to determine the total cure uptake. 

    Brine #1

    Nitrite/Nitrate concentration in the brine over time. (0, 7 and 14 days)

    Resulting cure levels in bacon

    Brine #2

    Nitrate/Nitrite concentration in the brine over time (0, 7 and 14 days)

    Resulting cure levels in bacon

    Summary of uptake. The axes have been adjusted to be the same in both graphs to make it easier to directly compare both of the methods. The horizontal area shaded in green is just for reference and shows the nitrite zone from 40 Ppm to 120 Ppm

    Conclusions from Lab test data
    • When immersed the loin and belly joints take up water at different rates - with the belly taking up the most.
    • Although the cure concentration in the brine reduced over time, the amount by which it reduced was consistent with an equilibrium being reached between the initial 5 litres of brine and the additional 0.7 litres of water from the meat tissues (meat being approximately 70% water)
    • The resulting cure within the meat using Brine #1 (% take up method) was between 550 Ppm and 600 Ppm after 7 days even though the weight increase was between 8%-11%. This level is 3-4 times the residual cure permitted by the USDA.
    • The resulting cure within the meat using Brine #2 (Pops equilibrium brine) was between 30 Ppm and 83 Ppm after 7 days and between 86 Ppm and 102 Ppm after 14 days. 14 days of curing in this brine resulted in a cure level which is almost mid point according to the USDA guidelines.
    • Based upon these test results, although the resulting bacon is unlikely to be harmful if eaten in moderation, the forum should consider carefully whether it is should continue endorsing the Brine #1 method as the resulting levels of cure were several times higher than the maximum USDA recommendations. At a minimum this should probably not be a method that is recommended to members who are new to curing.
    Updated to change the word "Cure" to "Brine" in the conclusion to avoid confusion.

    Updated to add the additional graphs with the same axis scales
    Last edited: Mar 11, 2015
    JC in GB and disco like this.
  2. Wow!  Thank you Wade for doing this test. I have used Pops brine for all I have wet cured, that certainly hasn't been a lot compared to others here, But I am pleased Pops had it right, and to have it confirmed is bonus! It isn't surprising the results of cure #1 are higher, but I am surprised how high. I'm new to brining/curing. Its comforting to see those numbers. Thanks again.
  3. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    Good work Wade...
  4. atomicsmoke

    atomicsmoke Master of the Pit OTBS Member

    Great work Wade. Thank you for your effort and £ spent.
  5. Hello Wade.  You know I am just starting to get into curing.  Thanks for all the hard work and expense you went to to bring us these results.  Just really helpful to see these sort of verified results.  Keep Smokin!

  6. pc farmer

    pc farmer Epic Pitmaster Staff Member Moderator OTBS Member ★ Lifetime Premier ★

    Thanks for the time and effort that you put into this.

    This proves that pops brine is VERY safe as he said it was.
  7. JckDanls 07

    JckDanls 07 Smoking Guru Group Lead OTBS Member

    Kudo's my friend... I've been following the whole time awaiting results.... "For me", I've always used, and trusted , Pop's brine ...

    I would like to point out one thing Wade... (as to not create any confusion between actual "cure #1 and cure #2).... In the "Conclusions from lab test data" ... could you change the wording so it will say "Brine #1" instead of "Cure #1" and then the same with Brine #2 instead of "CURE #2" ..... See where there could be possible confusion ??

    Thumbs Up
  8. supplysergeant

    supplysergeant Fire Starter

    Many thanks Wade. I know this cost you quite a bit in time, money, and frustration. It is very comforting to have this type of data available. I'll sleep better knowing I'm feeding my family safe products.
  9. Wade,
    I would also like to say thank you. I followed the other thread and was glad to see you started a new one for the outcome. Thanks again for taking the initiative/time/money to research this. I've learned several things from this study.
    Last edited: Mar 10, 2015
  10. wade

    wade Master of the Pit Group Lead OTBS Member SMF Premier Member

    Thanks for spotting that. I have updated it [​IMG]
  11. wade

    wade Master of the Pit Group Lead OTBS Member SMF Premier Member

    With all biological samples there will be variation and this is to be expected. From the moment each of the 20 litre brine stocks was split into the different joint samples they started on their own individual journeys. When looking at the cure remaining in the Brine #2 brines these were samples taken from different brine containers and were not sequential samples taken from the same brine container. Therefore is is not unexpected that variations from a "perfect" result will occur in a small number of samples. If the testing was performed using 10 or 100 joints at each stage for each brine then it would be expected that these small anomalies would smooth themselves out.

    What is important here are the orders of magnitude of the figures and not the precise numbers themselves. Due to biological variation if this exact testing were carried out again it is probable that the precise numbers would be slightly different with meat from a different animal. The consistency of these results though are sufficient that questions need to be raised regarding the Brine #1 method. Personally I would also raise the question whether Pops should slightly increase the levels of Nitrite in his brine to bring the resulting levels up closer to the 120 Ppm.

    The effective presentation of statistics is always difficult do and the axis chosen can be very influential on how they are interpreted. For the graphs above I simply let Excel choose the axis scales it wanted, and so it adjusted them to try to get graphs of the same size. Below I have recreated the graphs so that the axes scales are consistent, therefore giving a better direct comparison of the results and putting variations within the results in perspective.

    The horizontal area shaded in green is just for reference and shows the nitrite zone from 40 Ppm to 120 Ppm

    In response to Ghenges's question about pump brine concentration. This was information I received from the testing labs who questioned the low levels in Brine #2 - as they usually expect large scale bacon manufacturers to submit brine at the levels similar to Brine #1. All of these manufacturers though use injection/pump brining techniques and the labs are not aware of any using immersion commercially. This may be unique to the UK manufacturers and maybe not applicable in the USA.
    Last edited: Mar 11, 2015
  12. supplysergeant

    supplysergeant Fire Starter

    Well said, Wade. A very considerate response!
  13. chef jimmyj

    chef jimmyj Epic Pitmaster Staff Member Moderator Group Lead OTBS Member SMF Premier Member

    Interesting results. Thank you for your efforts Wade. Regarding the 625/660ppm vs. 200ppm residual Nitrite result, this was based on Brine #1 that contained Cure #1 consistent with the manufacturers recommended amount, 4 oz per Gallon Water. Is it possible that the max recommended Nitrite amounts for home use and commercial use be different? I don't think companies like SausageMaker would sell and recommend Cure amounts that would be toxic. I don't think following the recommended Cure #1 amounts should be discouraged on this forum but I do think any member responding to a newbies post encourage the new members to research curing meat in depth, before they attempt the process...Thoughts?...JJ
  14. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    I think, somehow, immersion cure and pumped curing brines have been confused... Pops, help us out here.... when your dad's business was operating... was there such a thing as "needle injection" pumping machines...... or was everything submerged equilibrium brining....

    I'm referring to mass production facilities.... Did your dad inject meats, other than ham legs...... was the brine a different make up.....
    Last edited: Mar 11, 2015
  15. wade

    wade Master of the Pit Group Lead OTBS Member SMF Premier Member

    Hi JJ

    Regardless of the actual resulting Nitrite levels, I think that 600-700 Ppm Nitrite will still actually be safe to eat in moderation. A 250g portion of the bacon (1/2 pound) at 650 Ppm would only contain 0.162g of Nitrite and as the lethal dose of Nitrite for a 65 Kg human would be in the region of 4.6 g, you would therefore need to eat about 14 pounds of the bacon over a short period of time to receive a potentially lethal dose. However I don't know what the cumulative effects may be of eting it regularly over a long period of time.
    As has been pointed out at various times on here, the UDSA guidelines actually only apply to the commercial manufacture of bacon and do not apply to bacon that is home produced. Therefore providing the cure manufacturers are selling it for home production then there is nothing stopping them from recommending cure dilutions that result in residual nitrite that exceed the USDA limits. The current rates of usage are probably traditional and proving you are not selling it then it is really up to you I guess what levels of Nitrite you feel comfortable eating. If you don't actually know the levels you are eating then then you will probably just be happy knowing/assuming that the levels recommended by the manufacturers are unlikely to do you any harm.

    I think my main concern now is that people may use the Brine #1 calculation and, based upon the calculated results, think that they have a much lover Ppm in their bacon than they actually have. 
  16. atomicsmoke

    atomicsmoke Master of the Pit OTBS Member

    The brine referenced here brine #1 (from the meat inspector handbook) was stated to work for pump or soak (immersion). Specifying that it should only be used for pumped and injected meat would avoid confusion.
    Last edited: Mar 11, 2015
  17. chef jimmyj

    chef jimmyj Epic Pitmaster Staff Member Moderator Group Lead OTBS Member SMF Premier Member

    Makes sense and what I was hoping to hear. I think there is often an unnecessary high level of worry that a few degrees of Internal Temp, minutes of Time in the Danger Zone or a couple of mg of Cure too much or too little, will render a hunk of meat inedible or dangerous requiring that it be immediately trashed. There is a lot of room for error between 0.162g and 4.6g...[​IMG]...JJ
    Last edited: Mar 11, 2015
  18. atomicsmoke

    atomicsmoke Master of the Pit OTBS Member

    Is the lethal dose the only concern? 500ppm will not kill you if eaten a few times but I doubt is good for one's colon to fry every Saturday meat with such high levels.
  19. chef jimmyj

    chef jimmyj Epic Pitmaster Staff Member Moderator Group Lead OTBS Member SMF Premier Member

    We know the lethal dose but we don't know exactly which number is unhealthy. The USDA guideline for commercial manufacturer's is 200ppm. Is 210 a problem, 250, 300, more, less? Wade's experiment gave a result, 600+. While I trust he was accurate in his measuring and testing, will this result be consistent for all pork products? What about Beef or Poultry? The forum admin wants us to follow the USDA guidelines. In this case the Cure manufacturer's instructions " were " followed. Can anyone at SMF prove that the instructions common to most of the US Cure #1 manufacturer's, reputable websites, curing book authors and so on are wrong?   It is the responsibility of the individual to do their homework before attempting any technique or recipe. We can only put out the facts as we know them to be true and not get into a heated debate with anyone having a different opinion. It will be up to the individual to take things further and determine the most accurate information and act on it accordingly...JJ
    Last edited: Mar 11, 2015
  20. cueinco

    cueinco Smoke Blower

    Wade, thank you very much for doing this work. As someone new to curing, it was confusing to see two very different approaches that would both "work", without understanding why they would work. Trying to match up results from the literature with experiences on this forum was confusing. This clears that up. Thanks again.