Wade, you are so quick to critique and criticize without the teensiest bit of research on your own....
Hi Dave. You and I have had a number of discussions where we have shared, compared and discussed resources and so I think this comment is somewhat unfair - although I probably do not read as extensively as yourself. I am expecting to retire next year and so will hopefully have more time then too. Having worked in analytical environments all of my working life (some of which have been in pharmaceutical research), although I do not class myself as an expert in any particular area when it comes to cure/brine chemistry, I am able to objectively look at claims and evidence that support them and gauge how much confidence we can have in conclusions reached. If the confidence factor appears to be low then the claims need to be challenged. Often when challenged more evidence then emerges that supports the claim and helps increase the confidence.
In order to try to support/verify your initial statement that we should "Never add acidic ingredients to a curing brine...." I have been re-reading some old papers that I had previously downloaded and came across a reference book that I had forgotten -
Modern Food Microbiology. If you do not have it I think that it will also be of interest to you.
Looking at the general post that you initially cited from Chefsteps, reviewing the chemistry of Nitrite and the results of my initial curing salts chemistry, I think that your conclusion regarding acid is completely valid when it comes to adding acid directly to curing salts, however It does not appear to be valid when it comes to adding it to a curing brine. In fact the opposite appears to be true.
You highlighted a very important factor which I think is easily missed and that is the order in which things are added in a brine. As Nitrite is readily broken down in highly acidic conditions then if you add any acidic ingredients to the curing salts before adding the main bulk of water then there is a very strong chance that the initial solution could be highly acidic and the Nitrite broken down before it can become active in the brine.
Regarding the action of the Nitrite as an antimicrobial, although the exact mechanism is not completely understood at the molecular level it is generally accepted that it is the nitrous acid that is formed when Nitrite is in solution that is the active antibacterial ingredient. On page 312 of the book, in the "Summary Nitrite Effects" it says "
Nitrite has a pK of 3.29 and, consequently, exists as undissociated nitrous acid at low pH values. The maximum undissociated state and consequent greatest antibacterial activity of nitrous acid are between pH 4.5 and 5.5.". This suggests that adding some acid to a brine is actually desirable to bring the pH to within this range.
It goes on to say that in ham (not Brine I know) that "
With respect to its <<Nitrite>> depletion or disappearance in ham... , Nordin found the rate to be proportional to its concentration and to be exponentially related to both temperature and pH. The depletion rate doubled for every 12.2◦C increase in temperature or a 0.86 pH unit decrease". This suggests that for every ~1 unit of pH more acidic the cure gets the rate of Nitrite depletion is more than doubled. The most desirable pH for the brine would therefore be the point where there is maximum antibacterial effect but where the depletion of Nitrite is at a rate where it is sufficiently available to do what is required. It needs to be remembered though that we tend to brine for periods of days/weeks and so it is may more beneficial to err towards the higher 5.5 pH (less acid) to give a longer period of time for the Nitrite to be active.
I have not heard back from Ellen yet but she says in the post that you cited "
You'll need to make sure the pH is 4.8 or above. If the Coca Cola is the only thing in the brine, it will be too acidic." This is consistent with the "optimum" pH range above. Maybe she has evidence that when you go below this pH the rate of Nitrite breakdown starts to have a more significant effect than the antimicrobial effect of the Nitrite itself. Also she does not say "do not add Coke" - just that neat Coke would be too acid. My bucket experiment shows that you could theoretically have up to 25% coke in the brine and still be within the "optimum" effective antimicrobial pH range.
As an aside Dave, a while ago we were discussing the rate at which Nitrite was lost with temperature. This book mentions "The Perigo Factor" which indicates that the initial amount of Nitrite before cooking is more important than the final residual amount. I think there is still quite a lot of academic "discussion" about this but you may like to look it up if you haven't already.
Back to your initial post. Would you be comfortable revising your statement to "
Never add acidic ingredients directly onto the curing salts" and recommending that the curing salts be the last thing that gets added to the brine? It would probably also be useful to identify the effects of acidic ingredients on the pH of a brine and give guideline recommendations based upon the probable effect on the final pH of the brine.