Last reviewed: 8 May 2026
The slow-release partner to E250 in long-cured bacon, ham and salami
If you've ever turned over a UK pack of bacon, ham or salami and seen both E250 and E251 listed in the ingredients, this is why. Sodium nitrate (E251) is the storage form. Sodium nitrite (E250) is the active form. Bacteria in the meat slowly convert one to the other over the weeks of a long cure, and that controlled drip-feed of nitrite is what gives traditionally-cured products their characteristic pink colour, flavour and protection against botulism.
Both end up triggering the same chemistry. When nitrite-cured or nitrate-cured meats are heated — frying bacon, grilling sausages, roasting a gammon — N-nitroso compounds form. Those compounds are why the World Health Organization's IARC classified processed meat as a Group 1 human carcinogen in 2015. The verdict applies to nitrate-cured products as much as nitrite-cured ones, because the chemistry funnels through the same intermediate.
This page is a label decoder for UK shoppers. We explain what each substance does in the curing chemistry, why dry-cured Parma ham uses E251 but supermarket wet-cured bacon usually doesn't, why "nitrate-free" celery-powder cured meats produce identical chemistry, and what the IARC and NHS guidance actually say.
Sodium nitrate is an inorganic salt with the formula NaNO₃ — a white crystalline powder. By itself it does very little to cured meat. It's not a direct preservative, it doesn't kill bacteria, and it doesn't create the cured-meat colour. What makes it useful is what bacteria in the meat do to it during curing.
The chemistry runs in stages:
So nitrite is doing the work. Nitrate is the slow-feed reservoir that keeps nitrite levels topped up for as long as the cure runs. In a fast wet cure (hours to days) you don't need nitrate — you can dose nitrite directly. In a long dry cure (weeks to months) you do, because nitrite added at the start would be exhausted long before the cure was finished.
Curing time is the deciding factor.
Short cures — minutes, hours or a few days. Most UK supermarket bacon and cooked ham is wet-cured: brine is injected into the meat, the meat is tumbled, the cure is finished within a day or two, then the product is cooked or smoked. There is no need for a slow nitrite-release reservoir, so manufacturers typically use sodium nitrite (E250) on its own. You'll often see only E250 listed on these packs.
Long cures — weeks to many months. Dry-cured products like Parma ham, Serrano, Bayonne, traditional UK air-dried ham, and dry-cured salami are buried in salt or rubbed with cure mix and left to mature. The cure has to keep nitrite present throughout that whole window. Adding nitrite alone would mean it was used up — by reaction, by reduction, by bacterial metabolism — long before the meat finished maturing. Adding nitrate as well lets the meat's own bacteria keep generating fresh nitrite throughout the cure. This is why dry-cured products typically list both E250 and E251, or sometimes E251 only with the nitrite generated entirely by bacterial reduction in situ.
If you see both E250 and E251 on a UK bacon or ham label, it usually means the producer is doing a longer or more traditional cure rather than a fast industrial one. It does not mean the product is doubly preserved or doubly chemical — the two additives feed into the same nitrite pool.
Less common than E250 in UK retail, but routine in the following categories:
UK and EU labelling rules require it to be declared on the ingredient list as "E251", "sodium nitrate" or "preservative: sodium nitrate". Where both nitrite and nitrate are used, you'll usually see both numbers in the preservatives line.
In 2015 the WHO's International Agency for Research on Cancer (IARC) published Monograph 114 on the carcinogenicity of red meat and processed meat. Its conclusion on processed meat was unambiguous: processed meat is Group 1 — carcinogenic to humans, on the basis of consistent epidemiological evidence linking processed-meat consumption to colorectal (bowel) cancer.
"Group 1" is the highest category IARC uses. It is the same category as tobacco smoking and asbestos. It does not mean processed meat is as risky as smoking — it means the evidence that it causes cancer is at the same level of certainty. Risk per portion and risk per cigarette are different conversations.
IARC's definition of processed meat covers any meat that has been transformed through salting, curing, fermentation, smoking or other processes to enhance flavour or improve preservation. Bacon, ham, salami, sausages, hot dogs, corned beef, biltong and pâté all fall inside it. The classification is on the category, not on a single additive — so nitrate-cured products and nitrite-cured products are both inside.
The mechanism most plausibly responsible is N-nitroso compound formation. When nitrite (whether added directly or generated from nitrate by bacterial reduction) reacts with amines from the meat protein, particularly under high heat (frying, grilling, charring), N-nitroso compounds form. Several of these are established animal carcinogens. The same chemistry can occur in the stomach during digestion. Both E250 and E251 feed into the same nitrite pool, so both contribute to the same risk pathway. Producers can reduce nitrosamine formation in-pack by adding ascorbate (E300 / E301), but cooking the product at high heat reintroduces the chemistry.
Source: IARC Monograph 114, Red Meat and Processed Meat, 2018 (working group review 2015).
Following the IARC finding, the NHS Eatwell guidance — drawing on SACN's 2010 Iron and Health report — advises that anyone eating more than 90 g of red and processed meat per day should cut down to 70 g per day. Seventy grams is roughly:
The 70 g/day cap is the official UK public-health number. We don't editorialise on it — that's the NHS line, available at the NHS Eatwell guide and the SACN Iron and Health 2010 report.
Most of the nitrate in a typical UK diet does not come from cured meat. It comes from leafy green vegetables: spinach, rocket, lettuce, beetroot, celery, chard. These can contain anywhere from 500 to 4,000 mg of nitrate per kilogram of fresh weight, far higher than the residual amounts in cured meat.
That sounds alarming until you read the chemistry. Vegetables come with vitamin C, polyphenols and other antioxidants in the same matrix. Those compounds are the reason vegetable nitrate does not produce the same nitrosamine load on digestion. EFSA's 2017 re-evaluation of nitrites and nitrates as food additives explicitly distinguishes the two exposure routes: vegetable nitrate is the larger source by mass but is not associated with the same epidemiological cancer signal as nitrate from cured meat.
The IARC processed-meat finding does not extend to vegetables, and the NHS 70 g/day cap is on processed meat, not on dietary nitrate as a whole.
You may have seen UK products labelled "no added nitrites or nitrates", "naturally cured" or "uncured bacon". Read the ingredient list. In most cases the cure is provided by celery powder, celery juice powder or another vegetable concentrate. Celery is naturally very high in nitrate (often above 1,000 mg/kg), and the cure works exactly as it does with sodium nitrate added directly: nitrate-reducing bacteria convert celery-derived nitrate into nitrite during curing, and that nitrite then reacts with the meat protein and pigment in the same way.
The chemistry is the same. The nitrite is the same molecule. The N-nitroso compounds that form on cooking are the same. The labelling distinction is meaningful for marketing and for some certification schemes, but it is not a chemical distinction — and the IARC processed-meat verdict applies regardless of whether the nitrate source is sodium nitrate (E251) or celery powder.
We state this neutrally. Buyers who choose celery-powder products may have other reasons (sourcing, additive avoidance for non-cancer reasons, brand preference). On the carcinogenicity question, "no added nitrate" cured meat is not chemically different from added-nitrate cured meat.
EFSA (EU food-safety regulator). The 2017 re-evaluation of nitrites and nitrates set the Acceptable Daily Intake (ADI) for sodium nitrate at 3.7 mg NO₃⁻ per kg of body weight per day. EFSA noted that exposure from food additive use is generally within the ADI for the average consumer, but flagged that some children's total nitrate exposure (including from vegetables and drinking water) can exceed it. The bigger overall contributor to dietary nitrate is leafy vegetables, not cured meat.
UK and EU labelling. Sodium nitrate must be declared on the ingredient list as "E251", "sodium nitrate", or under the preservative category, when used as an additive. Maximum-use levels in finished cured-meat products are set by Regulation (EC) No 1333/2008 and assimilated UK law.
FDA (US). Sodium nitrate is regulated for use in cured meat with maximum-residual-level limits and ingoing-level restrictions. It is permitted under the GRAS framework for the specific use of meat curing.
Regulatory approval for the additive is not a statement on the IARC processed-meat finding. The two operate on different questions: does the additive work and is its use level controlled (regulator), and what is the human-cancer evidence for the food category that contains it (IARC).
A few practical pointers for the supermarket aisle.
For the cancer-risk question, the most relevant line on the pack is not the E-number list at all — it's the product category. If it is processed meat (cured, smoked, salted, fermented), it sits under the IARC Group 1 finding, regardless of whether the cure used E250, E251, both, or celery powder. The NHS 70 g/day cap is the practical number to hold in mind. We track the totals so you can decide where you sit relative to it.
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