Foie gras oxidation & nitrite

[stickavish]

eGullet scientists,

I'm having a little trouble at work with some foie gras we are using oxidizing rather quickly.

The end result is a 1x1x3cm piece of terrine, although the word may not be exactly suitable for what we're doing.

The process is this (metric):

Separate the foie gras into lobes. Brine 24-48 hours in a milk/nitrite solution. I've tried a range of percentages, from 0.5% (5g /kg) - 1.0%, with not much discernible difference. Remove from brine, pat dry, season with salt, sugar, pepper, vacuum pack, cook in 65 C water bath until 55 C at heart. Shock, and then pass through a tamis to remove veins. It's then put into an even layer on a GN tray, cooled to set, and cut to specs. It yields a smooth, consistent, nearly waste-free product - with the exception of the rate of oxidation.

I have done the same process and yielded a product that remained a natural pink for up to 72 hours. I have done the process and lost the foie gras within 12 hours. I've done it and skipped the brine/nitrite altogether, which has yielded such a result that I question whether the brine/nitrite is even worth it. I've made a salt mix (94% salt, 6% nitrite) and then used this mix at 12g/kg dry. It created uneven oxidized patches on the liver. Chef de cuisine contends that putting it through the tamis, and thus exposing so much surface area, is the culprit. It makes sense, but i have reservations, as i have done this perhaps 75+ times, and gotten a beautiful result. There seems to be no consistency to the problem.

I have also been making a separate terrine, in a different process - tempering the foie gras, removing the primary and secondary vein, using a minimal amount of clean straight cuts, in order not to damage the foie gras, and then brining this. Seasoning the following day, mold in cylinder, wrap in film, cryovac, cook sous vide to 55, shock. This also seems to oxidize more quickly than it should.

Chef de cuisine, who recommended the brining, as practiced by french charcutiers, also mentions they are using saltpeter (potassium nitra/ite?), and possibly sugar, but it can tend to cause that bright pink unnatural look. I have ordered and received this, but another variable in this equation is that I am in mainland China, and am cautious about adding these chemicals to food, as i cannot guarantee that they are explicitly food safe - it goes without saying that we do not want to cause any harm to our customers.

Other possible variables - foie gras itself is locally produced (Shanghai). Purity of nitrite (?).

Thanks for any other suggestions.

[pounce]

I am NOT an expert and have not done anything like you are doing, however I have read that in the presence of lactic acid excessive nitrites can cause severe oxidation (oxymyoglobin). I think this is called "nitirite burn". I don't know if this is your issue or not. So, I guess one could look at the milk and the chemicals. Not knowing your chemical purity makes a person wonder.

I hope someone who knows better than I can chime in. Good luck.

[nathanm]

Nitrate generally acts as a preservative - both sodium and potassium varieties are used in meat products. It generally is food safe in the small quantities and concentrations you are using.

You could probably order some from elsewhere - or send a sample of yours out for analysis to check quality.

I agree with your chef de cuisine that exposing the fois gras to the air can't help matters. Whether it is the cause or not is another matter.

Have you tried brining with water instead of milk?

[pounce]

Shortly after my post I got a PM from the thread starter.

this was the only lead, and i'm glad to report that after months of battling this, it seems that the milk was the culprit. it was not so much a case of nitrite 'burn', at least not compared to some of the pictures i have seen of nitrite burn, but perhaps that was another mitigating circumstance. after eliminating the milk, and dropping down on the strength of my brine, i am getting a tremendously better result.

[andrewB]

foie is generally brined in a milk solution to help purify it, removing blood clots from the veins. This would not cause the oxidation, however i think the addition of the nitrites would. depending on quantity, it wouldn't be doing any better as a preserving agent than good old NaCl would be. I have always soaked my foie before making terrines and torchons and never had an oxidation issue..

Also 55C at center is way to high a temperature to take it to. try 110F(43C)...

[stickavish]

well, not a perfect resolution to this problem, i must admit.

on the suggestion here, i changed the milk/nitrite brine to a water/nitrite brine, at a 0.1% strength, i.e., 1g of nitrite per kilo water. this significantly reduced the oxidation, but did not completely stop it. i'm cautious to increase amounts of the nitrite.

a 55 C temp. has yielded a very good result thus far, which is 6+ months of daily operation from me, and years of doing to 55 C for the chef de cuisine. what exactly would be difference at 43 C? a creamier torchon/terrine, i'm assuming. does it affect it how solid it re-sets?

another question: in the last week or two, another chef has been doing it. he swears he is using the same method i demonstrated/explained, but the result has been a very crumbly and slightly more oxidized terrine. as he has also previously produced a fine result, i am a little stumped as to the cause of this - overcooking of the foie gras? over-brining? over-absorption of water into the liver during the brining?

thanks for all your suggestions so far.

[andrewB]

well, not a perfect resolution to this problem, i must admit.

on the suggestion here, i changed the milk/nitrite brine to a water/nitrite brine, at a 0.1% strength, i.e., 1g of nitrite per kilo water. this significantly reduced the oxidation, but did not completely stop it. i'm cautious to increase amounts of the nitrite.

a 55 C temp. has yielded a very good result thus far, which is 6+ months of daily operation from me, and years of doing to 55 C for the chef de cuisine. what exactly would be difference at 43 C? a creamier torchon/terrine, i'm assuming. does it affect it how solid it re-sets?

another question: in the last week or two, another chef has been doing it. he swears he is using the same method i demonstrated/explained, but the result has been a very crumbly and slightly more oxidized terrine. as he has also previously produced a fine result, i am a little stumped as to the cause of this - overcooking of the foie gras? over-brining? over-absorption of water into the liver during the brining?

thanks for all your suggestions so far.

←

crumbling and what your reffering to as over oxidation, to me says overcooked. Think of it in a similar vain to a steak: what happens to a steak when its cooked to medium well versus med rare? I think you'll find the same with the foie. The chef i worked with in Paris cooked his to 45, GD in SF took his to 43. what i found is that for terrines and poached torchons, 43 works like a charm.

As a side note, have you tried a salt curing for your torchon? i find that it is a much nicer torchon...