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Using Nitrite and Nitrate safely when curing


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Why do we sometimes use Sodium Nitrite when we cure?
The processes involved in “curing” meat and fish are carried out to extend the period of time over which the food can be safely eaten. The curing processes work by inhibiting the foods own autolysis enzymes and by inhibiting the growth of spoilage bacteria. This is predominantly achieved by increasing the salt content around the bacteria cells causing them to dehydrate through osmosis and also by reducing overall amounts of water throughout the food by evaporation through air drying/smoking.

Although most of the bacteria are readily controlled in this way, there are several types of bacteria that form spores that can be very resilient. Under certain conditions these spores will begin to produce toxins that can be incredibly toxic to humans in relatively small amounts. The presence of small quantities of Nitrite at >50 mg/Kg (or Parts Per Million - Ppm) will effectively inhibit the growth of these hazardous spore producing bacteria (e.g. C. Botulinum) 
Adding Nitrite will also delay the rancidification of fats that are present in the food. This ensures that the food also smells and tastes better for longer.
The presence of Nitrite also enhances the flavour and colour in the meat. It is responsible for giving bacon its “bacony” flavour and for its characteristic deep red colour. The flavour and colour can be achieved at levels of Nitrite as low as 15 mg/Kg (Ppm).
Over time the Nitrite is slowly broken down, or becomes bound up inside the meat, therefore reducing its preservative effect.

When do we use Nitrate in the cure?
Although Potassium Nitrate has been shown to also have a small inhibitory effect on controlling C. Botulinum, its main role is that it is slowly broken down over time to form Nitrite. This helps maintain the levels of active Nitrite within in the food being cured allowing it to be stored, often unchilled, for long periods of time (months). The products that would usually contain Nitrate in addition to Nitrite include Parma/country style hams and air-dried charcuterie (e.g. Salami and other air-dried sausage).
Nitrate when heated to high temperatures (e.g. when frying) can form Nitrosamines, which have been linked to cancer in rats. Because of this the use of Nitrates in bacon is banned in the USA and its use in meat that is to be “heat treated” is not permitted in the UK - except when used in certain “traditional” meat products. Whilst bacon is probably one of the highest risk foods for the formation of Nitrosamines when cooked, for commercial reasons it has been included in the list of “traditional” meat products. “Traditional” products though are limited to the amount of residual Nitrite and Nitrate that can remain in them after curing and the measurement of this is outside the capabilities of most home producers.

Isn’t Nitrite poisonous?
Pure Sodium Nitrite is toxic to humans when eaten in sufficient quantity. It would only require a person weighing 10 stone (64 Kg) to eat about 4.5 grams (half a teaspoon) of pure Sodium Nitrite for it to be potentially fatal. However, this needs to be put into perspective. To consume this amount of Nitrite by eating bacon that contains Nitrite within UK permitted levels you would need to eat AT LEAST 30 Kg of it at a single sitting. Although most vegetables have low levels of Nitrite some do contain high levels of Nitrate – which when eaten can be converted to Nitrite by enzymes and bacteria in the gut. Whilst the maximum permitted (Added) levels of Nitrite in bacon is 150 mg/Kg, some leafy vegetables (e.g. spinach and some lettuce) contain Nitrate levels up to 3,500 mg/Kg. Many commonly eaten vegetables (including cauliflower, carrots and asparagus) can contain Nitrate levels up to 1,000 mg/Kg.

Safe permitted levels
Once it has been added to the meat the Nitrite and Nitrate begin to undergo changes that makes it difficult to know exactly how much is present without the use of laboratory testing. Because of this the amount that we can safely use is calculated using the “Added” or “Ingoing” amounts. This ensures that the theoretical maximum levels of Nitrite and Nitrate are known, and with most immersion or dry cured meats the residual levels of Nitrites and Nitrates will actually be lower than this.

The maximum Added levels permitted in the UK are:
•    Nitrite 150 mg/Kg for most cured products but only 100 mg/Kg for sterilised meat products
•    Nitrate 150 mg/Kg but only for products that are not heat treated.

There are exceptions made to these levels for some traditional products however these are regulated by the amount of residual cure levels in the meat – which are not readily measurable by the home producer. 

If using PURE Sodium Nitrite then to add the maximum permitted added amount of 150 mg/Kg it would only require the addition of 0.15 grams to each 1 Kg of meat. This is far too small an amount to weigh accurately on most home scales and so the cures we use at home are usually pre-diluted with salt to make the amounts we need to weigh larger and therefore more manageable. For example when using Nitrite pre-diluted as Cure#1 we would need to add 2.4 grams per 1 Kg of meat to achieve 150 mg/Kg.

The use of pre-diluted cures also adds to the safety. The photo below shows the potential fatally amounts of Cure #1 (left) and pure Sodium Nitrite (right) for a 10 stone (64 Kg) person. 

5a01ab76b8577_Cure1vsNitritelethaldoses.thumb.jpg.0e282ff064e8c1ba605c13c53160b6e9.jpg

Common types of pre-diluted cure mixes

Common names

Contains

 

Maximum cure permitted per Kg *

Cure #1
Prague Powder #1
InstaCure #1

Sodium Nitrite
Salt

6.25%
93.75%

2.4 grams

Cure #2
Prague Powder #2
InstaCure #2

Sodium Nitrite
Potassium Nitrate
Salt

6.25%
4.75%

89.0%

2.4 grams

Morton Tender Quick

 

Sodium Nitrite
Sodium Nitrate
Salt, Sugar and Propylene Glycol

0.5%
0.5%
99.0%

30 grams

Supracure

 

Sodium Nitrite
Sodium Nitrate
Salt

0.6%
0.6%
98.8%

25 grams

* When dry curing this is the weight of the meat. When immersion curing this is the weight of the meat plus the weight of the water used in the brine. When using the cure as an ingredient this is the weight of all of the ingredients combined. 

Although the above table shows the recognised standards used for these cure mixes in the UK, sometimes suppliers can deviate from these proportions. It is therefore important to check the label for the exact contents of every cure that you buy.

Just as important as the cure content is that you should only buy it from a reputable source. Only buy your cure from a recognised commercial supplier - and preferably one who can provide laboratory test certificates for the batch of cure that you are buying. 
If you buy from unknown “cheap” suppliers online you really do not know what you are buying. Inconsistent mixing of the cure batches can result in your cure having either significantly more or less of the curing ingredients than you are expecting. I even have experience where the Cure #1 I purchased through a supplier on Amazon actually contained NO Nitrite at all.

How do I calculate how much cure to use?

The most important thing to remember when using cure that contains Nitrite and/or Nitrate is DO NOT GUESS. You should never just sprinkle the cure over the meat and hope. It is important to know how much of the active ingredients you are adding to your meat.

One of the simplest ways of calculating your cure ingredients is to use one of the online cure calculators – a couple of tried and tested ones are shown below.

www.localfoodheroes.co.uk
www.diggingdogfarm.com

It is also very straightforward to calculate the cures manually with sufficient precision. The examples below assume we are using Cure #1 and, whilst the curing purists amongst us could argue that the calculations below are not exact, we are dealing here with biological systems where things do not function “exactly”. The calculations, although simplified, are sufficiently accurate to ensure that the cure used is calculated safely.

Dry Cure – assuming 2 Kg of pork and a salt level of 2.5%

•    For each 1 Kg of meat we require 2.4 grams of Cure #1, therefore for 2 Kg of meat we require 4.8 grams of cure.
•    For each 1 Kg (1,000 grams) of meat we require 25 grams of salt to achieve levels of 2.5%, therefore for 2 Kg of meat we requite 50 grams of salt.
•    As the cure #1 is actually 93.7% salt we can assume that it is almost all salt and therefore we need to subtract this from the weight of the salt that we are adding
•    Therefore, our basic dry cure will consist of 4.8 grams of Cure #1 and 45.2 grams (50 - 4.8) of salt.


Immersion Cure – assuming 2 Kg of pork, 3 litres of brine and a salt level of 2.5%

•    The total weight of the meat and the brine is 5 Kg - 2 Kg of meat + 3 Kg of Water (1 Litre of water weighs 1 Kg)
•    For every 1 Kg of meat and brine we require 2.4 grams of Cure #1, therefore for 5 Kg of meat and brine we require 12 grams of cure.
•    For each 1 Kg (1,000 grams) of meat and brine we require 25 grams of salt to achieve levels of 2.5%, therefore for 5 Kg of meat and brine we requite 125 grams of salt.
•    As the cure #1 is actually 93.7% salt we can assume that it is almost all salt and therefore we need to subtract this from the weight of the salt that we are adding
•    Therefore, our basic brine will consist of 3 litres of water, 12 grams of Cure #1 and 113 grams (125 - 12) of salt.

If you wanted to add sugar to either of these cures it is best used at a rate of 50% of the salt. For the dry cure example you would add 25 grams of sugar and for the immersion cure you would add 62.5 grams of sugar.

Once you have increased your confidence in the curing process you can then begin to experiment. Remember though that the incorrect use of cure can be hazardous and so if in doubt ask. There are plenty of people in here and in other forums with the knowledge and expertise to be able to help you proceed with confidence. 

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Once again Wade, a fantastic description on using Nitrite and Nitrate safely.

Some people may thing why do I need to know this stuff? 

As long as you know the basics and stick to the guidelines then everything will be safe.

I’ve read about people curing bacon with shop bought cure, that keep adding more cure everyday.

Practises like this is very dangerous to human life, and that’s whey Wade and myself look at how people are curing and will comment on their procedures good or bad. 

We are not the Curing Police, we simply want people to stay safe and enjoy there Home Cured Products.

 

 

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I am starting to do some cold smoking beyond the basic cheese, salmon etc, and your commentsabove, Wade, are very useful.  One question, though - accuracy of weight is obviously highly important, so can you recommend any scales that will measure to decimal points in grammes?

TIA

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So long as you are using Cure#1, #2 or another pre mix (rather than pure Nitrite) then digital scales that are accurate to 0.1 gram are absolutely fine. These can be bought from most kitchen suppliers. I have a couple of scales I use - one is a Salter and the other is a Heston one which I bought from John Lewis. You don't need to spend a fortune and you should be able to pick some up for <£30. Here is one from Argos http://www.argos.co.uk/product/2785763 that would be fine.

With the safety margins involved even if you were to measure to the nearest gram you would be fine - but it is whatever you feel most comfortable doing. Personally, I prefer to go to the nearest 0.1 g.

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  • 10 months later...
On 11/7/2017 at 1:08 PM, Wade said:

 

Dry Cure – assuming 2 Kg of pork and a salt level of 2.5%

•    For each 1 Kg of meat we require 2.4 grams of Cure #1, therefore for 2 Kg of meat we require 4.8 grams of cure.
•    For each 1 Kg (1,000 grams) of meat we require 25 grams of salt to achieve levels of 2.5%, therefore for 2 Kg of meat we requite 50 grams of salt.
•    As the cure #1 is actually 93.7% salt we can assume that it is almost all salt and therefore we need to subtract this from the weight of the salt that we are adding
•    Therefore, our basic dry cure will consist of 4.8 grams of Cure #1 and 45.2 grams (50 - 4.8) of salt.

 

Using the Diggindogfarm calculator I am struggling to match those figures. What ppm Nitrite figure are you using.

To get 2.4 grammes of cure I need to drop the Nitrite figure down to 150 for a kg piece of pork but the salt at 2.5% shows 22.75g which would drop the the normal salt added down to  20.35g after cure amount subtracted. This is clearly less than your figures, so I must doing something wrong?

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Comparing the 2 calculators localfoodheroes (EU Setting) and diggingdogfarm side by side (localfoodheroes has no Nitrite adjustment) they give quite different cure results based on typing in  1kg of pork keeping their initial default settings but changing salt to 2.5% on diggingdogfarms to match the localfoodheroes one?

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The Nitrite in the calculation is 150 Ppm

Using my calculator you get the following

image.thumb.png.dac684ec19324208192ce2227f9a9450.png

Using Martins (DDF) calculator you get the following

image.thumb.png.719c9738e7c6ea6e18a8a45f134598f2.png

Both give the required amount of cure to be 2.40 g
My calculator gives the added salt required to be 22.6 g and DDF gives 22.75 g. These are to all intents and purposes the same and the difference will be down to rounding in the calculations. My calculator is in Excel and so probably just calculates to more decimal places than DDF.

As the amount of salt shown in the calculators already accounts for the salt added in the cure, you do not require to subtract the cure weight from the salt weight shown.

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You can check the calculations for yourself using the following formula

To calculate the amount of pure Nitrite...

<Weight of Nitrite> = <%Nitrite in cure> * <Weight of Cure > / 100
Weight of Nitrite = 2.4 * 6.25 / 100 = 0.15

To calculate the resulting Ppm from that amount of Nitrite...

Ppm = <Weight of Nitrite> / <Weight of meat> * 1,000,000
Ppm = 0.15 / 1000 / 1,000,000 = 150
 

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6 minutes ago, Wade said:

The Nitrite in the calculation is 150 Ppm

Using my calculator you get the following

image.thumb.png.dac684ec19324208192ce2227f9a9450.png

Using Martins (DDF) calculator you get the following

image.thumb.png.719c9738e7c6ea6e18a8a45f134598f2.png

Both give the required amount of cure to be 2.40 g
My calculator gives the added salt required to be 22.6 g and DDF gives 22.75 g. These are to all intents and purposes the same and the difference will be down to rounding in the calculations. My calculator is in Excel and so probably just calculates to more decimal places than DDF.

As the amount of salt shown in the calculators already accounts for the salt added in the cure, you do not require to subtract the cure weight from the salt weight shown.

That has reassured me thanks. The taking off the cure amount from the salt threw me, reading through your post. But as you you say the calculator does that for you automatically. Out of interest do you have a rough idea what Nitrites ppm bog standard Smoked supermarket bacon runs at?

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23 minutes ago, Justin said:

Good discussion because I agree the cures has salt in o think so must be taken into account. I find cures too salty and I have to rinse tons.  

Pepper has been my problem in the finished flavour as it is is too strong for me (szeuchuan or black peppercorns grinded) Last couple of attempts I have used Tellicherry Peppercorns and it provides a pleasant finished aromatic and slightly citrusy flavour to the bacon, without the heat of the others I have tried. Available at most supermarkets

A blog on the difference between Black and Tellicherry peppercorns here if interested Tellicherry I use it as a replacement in my homemade rubs and brines now as well. But I am a bit of a wimp when it comes to spicy or heat in my food and don't have the palate for it, so glad to have found a less strong and more aromatic alternative.

 

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1 hour ago, sotv said:

 Out of interest do you have a rough idea what Nitrites ppm bog standard Smoked supermarket bacon runs at?

Before I answer that we need to be clear about what we mean by ppm. When we are curing the bacon we are applying the Nitrite at a specific concentration - called "INGOING" or "ADDED" Nitrites. This is different to the amount of Nitrite that actually occurs in the end product - "RESIDUAL" Nitrite. Both are measured in Ppm but both will be different. Curing meat is not an exact science as we are dealing with variations in biological systems and the residual Ppm could be either higher or lower than the ingoing Ppm.

For example... If we apply Nitrite at a rate of 150 Ppm during the curing phase, not all of it will be taken up and some will remain in the brine surrounding the meat. The Ppm of that which is taken up into the meat will change depending on what we do to the meat as we are processing it - as we lose moisture during the salting, hanging or smoking phases the Ppm of the nitrite that is taken up will increase as the overall weight of the meat decreases. Some of the Nitrite will also be metabolised. When we finally cook the meats before eating more water will be lost but also the Nitrites will be broken down by the heat.

The reason we calculate the amount of Nitrite as "Ingoing/Added" nitrite when curing is that this is something we can measure. It is impossible to know the "Residual" Nitrite of the food without having samples lab tested - which for most producers is simply impractical.

Here is a link to the FSA Food additives legislation and guidance where on page 26 (bullet point 69) it tells us " the legislation limits the use of potassium and
sodium nitrite in meat products to a maximum amount added of 150 mg/kg
". however it also says in bullet point 68 that "However, a degree of compromise has been introduced in the legislation in order to allow the continued production of certain traditional products. These compromises include provisions which permit traditional UK meat products such as Wiltshire cured ham, bacon and similar products to be produced based on residual amounts." as these are traditionally made using Nitrite levels higher than the recommended ingoing maximum.

Up until a few years ago the maximum amount of ingoing Nitrite in the US and EU was ~170 Ppm but this has subsequently been reduced to its current levels. These levels are set to protect the most vulnerable amongst us - and those that eat a lot of processed meat. This is very reassuring as it is clear that there are large margins of safety built into the legislation. If we make our bacon using ingoing Nitrite at 151 Ppm it is not going to poison us and if we only use 149 Ppm we are not going to die from Botulism poisoning. When making our bacon at home (non commercially) then we would ideally want to use 150 Ppm but if we are somewhere between 125-175 Ppm that that is fine too.

Now to answering your question...

Most supermarket bacon is pump cured as it speeds up the curing process and so increases throughput. This is done by making a brine that is ~10x the concentration if the required ingoing Ppm and then injecting the meat with brine that is equal to 1/10th of its weight. This has 2 advantages for the producer - It gives a faster cure and the added water increases the weight of the bacon that is produced. The amount of brine injected will work on averages, as each piece of meat will not weigh exactly the same, and their specific process will have been approved by their local FSA inspector. Most will be producing their bacon at between 125-150 Ppm in order to maximise the colour.

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1 hour ago, Justin said:

Right, I get it know.  Are you able to share your spreadsheet mate so we can do our own calcuations without bothering you?

It will not allow me to upload Excel files here. I will rename a version when I can and upload it.

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Another quick question for information thanks. |I have always used Kosher Salt for the curing as it is a pure form of salt with no additives or caking agents. I have recently bought some Cornish Sea Salt to try in rubs, it is meant to be all Natural with no additives, but considerably larger flakes, do they need grinding if so. Can you use it as part of the cure mix or am i best sticking with the Kosher?

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There is a bit of a myth and some snobbery when it comes to the differences between salts. It is very rare that the salt we buy is actually pure Sodium Chloride (NaCl) as commercial cooking salts are either mined or evaporated from the sea. In fact all natural salt is actually sea salt as even the mined salt was formed by oceans that evaporated millions of years ago. The salt we eat is predominantly Sodium Chloride but depending on where it has come from it will have differing amounts of  "impurities" (0.2%-10% other salts) which give each their particular qualities.

Kosher salt is no different in composition to many other types of salt - it is simply the shape of the crystals that distinguish it. The reason it is called Kosher salt is that the shape of the grains make it ideal for use in the meat koshering process. The sea salts typically contain more impurities than the rock salts however these impurities should not be seen as something bad. The impurities are what give the "speciality" salts their distinctive tastes. There is a myth too about some salts being "saltier" than others as most differences in perceived saltiness are down to the way the salt grains interact with our tongues. Course salt is often used when plating up to give specific concentrated bursts of salt flavour without making the overall dish taste over salty.
The grain size will also affect the amount of salt added and it is important that salt is weighed if you are looking for consistency of flavour. The example below shows the different weights of 1 rounded tablespoon of different types of salt...

  • Table salt    12 g
  • Diamond kosher salt    9 g
  • Morton kosher salt    17 g
  • Maldon salt    9 g
  • Sea salt    20 g
  • Hawaii Gold Sea Salt    17 g

The differences in weights are due to the size of the crystals and also their shape - which allows some to pack together more efficiently.


When it comes to using salt in a cure or a rub then, to be honest, the only salt you should probably avoid is table salt as it has been iodised and this has been reported to give a flavour taint when used in curing delicate meats/fish. However, on the rare occasions I have used it I have not found this to be the case. Whether a salt has an anti-caking agent will depend on the size of the grain in the pack. Almost all fine salts will contain an anti-caking agent as this is necessary to absorb moisture and prevent the salt from solidifying into a block. The actual anti-caking agent used will depend on the salt producer but all have been declared safe by both the US FDA and the UK FSA. Most large grain salt will not need an anti-caking agent. If you want to use a specific type of salt that does not have an anti-caking agent added you will usually need to buy it in its course grain form and then grind it yourself. If you look hard you can find some fine salts with no additives but they are not common. 

For all of my curing I use plain old supermarket fine cooking salt. Whilst it does not have added iodine salts it does contain an anti-caking agent. For my rubs (where taste is more important) I use course grain Dead Sea salt which is then ground fine with all of the other ingredients. I buy the sea salt in 25 Kg sacks and to indicate how "pure" sea salt is... I frequently find small salt-grain sized stones still in it. 

There is a lot of snobbery when it comes to which salt to use and it really depends on what you are using it for as to which you buy. If you are preserving a big barrel of salt beef then it is traditionally done using course grain salt called "Corns" (yes the origin of the phrase "corned beef") however if you are curing a single piece of meat or fish then you are best using fine grain salt to ensure an even coverage. When making a rub then you will almost always use a fine grain salt that is then reduced to a powder.

To answer your question, you could use either the Kosher salt or the Cornish sea salt but as they both have course crystals they are both best ground before using as a cure. Will there be any noticeable difference to the end result - almost certainly not. Use whichever you feel most comfortable with :thumb1:

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Thanks for the detailed and informative  reply. I am no salt aficionado, but I do feel sea salt tastes for instance different on the tongue almost sweet, rather than salty in its raw form to say cooking salt, but that may just be my palate.

I tend to use the Diamond Kosher salt for my needs, but I take your point about how little difference there is overall, you jut get used to something and comfortable with it, that works for your needs. I have always been wary about the amount of fillers used in some normal salt and the reason, why I chose to use this. 

The link you provided for the fine salts, no additives has been bookmarked for my next order. Already use this site regularly for my paella spices and rice and they have the more unusual ingredients I have used recently like Wild Fennel Pollen and Raspberry Vinegar for some of my different smoking attempts. I think it is an excellent site has some hard to find ingredients and reasonable prices to.. 

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9 minutes ago, sotv said:

I have always been wary about the amount of fillers used in some normal salt and the reason, why I chose to use this. 

These should not be considered as "fillers" but more as a texture preservative. Without them any salt left open to the air would quickly start to clump. Even salt with added anti-caking agents that is left open to the air in a humid kitchen will soon begin to form solid lumps of crystals. A common anti-caking additive that is used in restaurants is rice. You often see rice grains that have been added to the salt shakers on the tables to stop it from clumping.

As you say, in the end it comes down to personal preference :thumb1:

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7 minutes ago, Justin said:

And of course in brines the salt dissolves anyway? So the crystal structure is irrelevant.

True, but it is more common for fine salt to be used when making brines as it dissolves more easily in cool water. I have tried making immersion brines using course sea salt and no matter how much you stir it never seems to fully dissolve... Obviously it does all dissolve eventually but it can take a long time!

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Yes as this will help to ensure that the cure is homogeneous and will coat the surface of the meat evenly. I have a "Waring Commercial" spice grinder which has removable grinding bowls and so when making a dry cure just I weigh all of the ingredients (salt, cure, sugar and any spices) together straight into the spice grinder bowl and then blitz it to a fine powder before applying.

Image result for Waring Commercial WSG30K Spice Grinder

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