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Found 8 results

  1. I've had some success curing & smoking my own bacon over the last few months (both streaky & back) using a couple of different cures (one fairly plain with juniper, bay, pepper) and one sweeter with maple syrup but I'm always interested in finding new and unusual cures & smokes to use. Has anyone got anything a bit left-field that they can share that works well? I've mainly smoked in cherry and maple.
  2. Hi all. New member from Manchester here and new to smoking & curing. Got the bug after doing a course down at River Cottage in February. Have had some success with my own smoked bacon and currently have my first air-dried ham (speck) hanging in the shed which will be ready in a few months (as long as I've got the cure right!!!). I have a question regarding a brine though and thought someone on here might be able to help. I have had a boned out leg of pork brining in cider & apple juice for the last 10 days. I have used the correct amount of salt etc and the ham appears okay (I have removed the ham this morning) but there were some small specks of mildew on the brine surface when I removed it. I am hanging it for 24 hours before smoking & cooking. Will it be okay to eat or does the mildew signify that the meat is spoiled? It was completely submerged for the whole time in a bucket in the house (too big for the fridge). Any advice appreciated.
  3. 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. 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.
  4. My main fridge has unexpectedly given up the ghost and I have been forced to replace it. That has now left me with a stainless steel fridge that will be perfect to convert into a curing cabinet. I will need to add some temperature and humidity control and ventilation but it should do nicely. I now just need to find the time to actually get around to converting it... Oh yes... and somewhere to put it that is acceptable with SWMBO
  5. Time to Cure and Cold Smoke your own Bacon. "FORUM WARNING" Once you have made your own Bacon, you will not buy Supermarket Bacon again! Curing and Cold Smoking Bacon
  6. Using Nitrite and Nitrate safely when curing
  7. To begin the Smokevember month here is an explanation of the roles of the different processes used in curing and preserving. Everyone who cures, smokes or preserves food will use a combination of these methods, often without realising why. When you first begin curing food it can be quite stressful to know whether, what you have just created, is safe for you or your family to eat. However, with even a basic understanding of what you are doing will help you to eat with confidence. The saying "If in doubt chuck it out" is generally good advice, however this can often lead to food that is perfectly safe to eat being thrown away. Fitstly, the more you understand about the processes the less doubt you will have and therefore the less that will be "chucked". Secondly, there are a lot of people who cure and preserve food regularly who are here and can offer you advice. I would therefore recommend that the advice be updated to "If in doubt ASK before you chuck it out" What is curing when applied to food? Curing is a method of preserving food to prevent spoilage. It refers to various preservation and flavouring processes, especially of meat or fish. Spoilage can be prevented (or delayed) by using several processes. Most curing processes involve applying a combination of these to achieve the desired taste, texture and storage time. Sometimes the extended storage time is only measured in days (as in traditional smoked salmon), weeks (as in dry cure bacon) or months/years (as in jerky, salamis and Palma/Country style hams) The different processes that can be used in combination: Reducing available water – including dehydration The growth of bacteria and bacterial spores is significantly affected by the availability of water in their surroundings. Water is also required by the natural enzymes in foods that cause autolysis – the self-destruction of cells by their own enzymes. If the water is removed or made unavailable, the storage life of most foods will be prolonged. Although we could totally remove the water from the food to have the preservative effect, it only really needs it be made unavailable to the spoilage organisms/enzymes. This can be done though several different processes. Removing the water – This is often achieved by warming the food in a relatively dry environment which enables the water in the food to evaporate. The smoking process is a good example of this, where the air that includes the smoke passes across the surface of the food causing the water to evaporate and pass out of the chamber with the smoke. This is why is us usually important to maintain good air flow through your smoker when cold smoking. Changing the state of the water – For bacteria to utilise water it must be in liquid form. One of the effects of placing food into a freezer is that it changes most of the water into ice and therefore make is unusable by bacteria. Freezing, however, does not remove liquid water completely as even when frozen some of the ice will be transitioning from solid to liquid and then back to solid. The lower the temperature in the freezer the less water there will be in liquid form at any point in time. Removing water from the bacteria cells – This is done by increasing the amount of salt and/or sugar around the bacteria, causing the water within their cells to be drawn out by a process called Osmosis. The removal of water from the cells prevents the bacteria from metabolising and growing and often results in their cell walls rupturing and the bacteria being destroyed. Binding the water – Various substances, including sugar, will chemically bind large quantities of water to their molecules and will therefore make it unavailable to the bacteria. This process is one of the important steps when making a BBQ sauce or ketchup that is not going to be eaten immediately. There is still water within the sauce so that it remains pourable, however much of it is bound to the sugars that are also present and which become more concentrated as the volume of the sauce is reduced through simmering. As you can see, you do not need to physically remove the water from the food to have a preservative effect - You just need to make it unavailable for any spoilage organisms to use. Jargon alert: The available water in food is known as Water Activity (aw) and to totally inhibit most spoilage bacteria and moulds an aw of 0.8 or below is required. Many commercial food processers will use an (aw) meter to check that their products are safe for long storage, however these are very expensive and are outside the pockets of most home curers. Even though most home curing processes will not achieve an (aw) of 0.8 or below, there will still be a preservative effect, though more limited, at higher (aw) levels. Increased Salinity – adding salt Salt is usually added in one of three ways – applying directly to the outside (Dry Brining), applying as a liquid solution (immersion brining or injecting), adding salt as an ingredient. There are several ways in which salt will inhibit microbial growth. The most notable is through osmosis, or dehydration (see above). Salt’s other antimicrobial mechanisms include interference with a microbe's enzyme activity and weakening the molecular structure of its DNA. When used as an effective bacterial inhibitor it requires salt solutions of ~10% to make most food spoilage organisms inactive, however salt at this concentration in our food would be unpalatable. Lower salt concentrations will also reduce bacterial growth but to a lesser extent. Many bacteria are very hardy organisms though and as salt concentrations fall the activity of many will again begin increase. The ways of applying salt through the differing curing methods will affect the storage time of the final product. A good example is the difference between Dry cured and Immersion cured bacon. Both methods can be used to produce an end product that contains 2.5% salt, however the resulting shelf life of both methods is very different. Unsliced Dry cure bacon can be safely stored refrigerated for up to 6 weeks whereas the equivalent safe storage life for immersion cured bacon is only 2 weeks. One of the reasons for this is the levels of salt that the bacteria are exposed to during the curing process. With Immersion cure bacon the levels of salt in curing solution will depend on the volume of immersion cure being used and the weight of the meat however it will usually not exceed twice the desired end concentration – therefore will rarely exceed 5% (and will frequently be lower when using larger volumes of cure solution). Although this will inhibit the growth of most bacteria it will not inhibit it completely. When Dry curing bacon you are applying crystalline salt directly onto the surface of the meat – where most of the bacteria will be present. As this salt dissolves in the water from within the meat it results in the surface bacteria being exposed to a saline solution of 100%. As the salt diffuses towards the middle of the meat this concentration will reduce however during normal curing times the surface brine concentration is unlikely to fall below 10% until the salt concentration in the meat is fully equilibrated. Another difference between the two curing methods is that the process of immersion curing will result in an increase in the water content of the meat by about 10%, whereas the process of dry curing will decrease the meat water content. Commercially the levels of salt in brining solution will be measured using a saline meter. These are fairly inexpensive and are often affordable by the home preserver. The electronic salt meters are best as they measure the salt through its ionic properties. Another common saline meter is an optical refractometer. These should ONLY be used for saline solutions that do not also contain sugars, as the presence of sugar will make the resulting "salt" readings highly inaccurate. Increasing sugar Sugar will have a similar osmotic effect on the bacteria cells as salt, causing them to dehydrate, however sugar molecules will also bind water molecules lowering the (aw) and making them unavailable for the bacteria to use. Sugar may also provide an indirect form of preservation by serving to accelerate accumulation of antimicrobial compounds from the growth of certain other organisms. Examples include the conversion of sugar to ethanol in wine by fermentative yeasts or the conversion of sugar to organic acids in sauerkraut by lactic acid bacteria. Increasing acidity (decreasing pH) Increasing the acidity of foods, either through fermentation or the addition of weak acids, has been used as a preservation method since ancient times. In their natural state, most foods such as meat, fish, and vegetables are slightly acidic while most fruits are moderately acidic. Only a few foods such as egg white are alkaline. Generally most food spoilage bacteria thrive within a narrow pH range and as you move away from this range they become increasingly inhibited. The effect differs though between organism. For example, a pH of 4.6 is sufficient to control most spore forming organisms (e.g. C. Botulinum) however a pH of 4.2 is required to control other vegetative pathogens (e.g. Salmonella). Increasing the acidity (reducing the pH) can be achieved in several different ways. The adding of an acid directly (e.g. Vinegar in sauces, pickles and chutneys), adding acidic fruit or juices (e.g. orange juice pH 4; lemon/lime juice pH 2; tomatoes pH 4.2) or adding a bacteria that increases the acidity of its environment as it grows (e.g. the use of a lactobacillus in salamis) Commercially the acidity levels are monitored by using a pH meter and these are inexpensive and can often be afforded by the home curer. Addition of Nitrite (and sometimes Nitrate) When added to foods such as cured meats, nitrite has at least three functions. Firstly, it contributes to the flavour - the nitrite is responsible for imparting the characteristic “bacon” flavour. Secondly, it reacts with myoglobin in the meat which gives the characteristic pink colour of cured meat. Thirdly, it inhibits the growth of food spoilage bacteria, most importantly Clostridium botulinum. The chemistry of nitrite when curing meat is quite complex and the exact mechanism by which it inhibits the growth of C. Botulinum is still a matter of scientific discussion. Nitrite is known to be effective at levels of less than 50mg per Kg of meat. Without laboratory analysis it is not possible to know with certainty how much of the nitrite remains in the meat following the curing process, as within the meat it will undergo a number of different reactions where it can remain free, be bound up byother molecules or cell components, it can be metabolised and broken down. Because of this the use of Nitrite in curing is actually calculated using “ingoing” amounts of Nitrite. Until a few years ago permitted Nitrite levels were ~350 mg/Kg (Ppm) however recently the EU, FSA and USDA have reduced the limits of ingoing nitrite to 150 mg/Kg (Ppm) for uncooked cured meat (and 100 mg/Kg for cooked meat). There are some exceptions for some traditional regional products where higher levels of Nitrite are permitted, however these exceptions limit the amount of residual nitrite in the meat which would have to be established through laboratory testing. As nitrite is gradually broken down in the food it will lose its effectiveness if time for controlling C. Botulinum. For foods that are stored chilled and have a short shelf life this is not a problem however for longer term storage (e.g. Parma/Country style hams and salami style sausages) Potassium Nitrate is also added. The nitrate does not play a direct role in the biological control but over time it is slowly broken down to form Nitrite, replacing the nitrite levels as they are lost. In the USA the use of Nitrate in bacon is no longer permitted as, when heated to high temperatures (e.g. when bacon is fried), the nitrates are converted to nitrosamines which have been linked to cancer in rats. In the UK the situation is less clear however the FSA stipulate that “The use of potassium and sodium nitrate is permitted only in non-heat-treated meat products, to a maximum amount added of 150 mg/kg”. Frying bacon before eating would be considered a heat treatment. Unfortunately, some of the manufacturers of ready-to-use cures (e.g. Supracure) have yet to change their usage instructions to comply with current regulations. When used at the recommended 5%, Supracure will result not only in an ingoing Nitrite level of >300 mg/Kg and will result in Nitrate being included in the bacon cure, but it will also produce a salt level of 5% which most people will find unpalatable. Exclusion of oxygen Preventing oxygen from reaching most bacteria will stop them from growing and increase the shelf life. This can be simply achieved by vacuum packing but can also be achieved by canning. The use of set sugar can also be used to form an oxygen barrier, as in jam. Care needs to be taken when excluding oxygen, as spore forming bacteria (e.g. C. Botulinum) require an oxygen free environment to produce their toxins. It is therefore important that food that is going to be stored this way should also have additional methods of spore control. This could be the use of added nitrite, by reducing the pH through pickling, or by suitable heat treatment. Heat treatment The only way to ensure that your food is effectively free of food spoilage organisms is to heat treat it, although this requires specialist equipment as some bacteria spores (e.g. C. Botulinum) are not killed by boiling water. At 120 C in a pressure cooker/canner (retort) it will take between 10 and 30 minutes kill the C. Botulinum depending on the acidity of the food. Chilling or Freezing The storage life of most foods can be extended by chilling or freezing. Although freezing would appear to be just an extension of chilling they actually work in different ways. The process of chilling food results in the slowing down of the metabolism of food spoilage organisms so that their effect is delayed. Even when chilled to 4 C they will still remain active and will eventually result in the food becoming unsafe to eat. The chilling effect is on both vegetative and spore forming bacteria. When stored at 4 C or below it will take C. Botulinum in excess of 10 days to produce levels of toxin that could begin to become hazardous to vulnerable individuals. The process of freezing works in three ways. Firstly, it continues to reduce the metabolism of the bacteria. Secondly it changes most of the available water to ice which cannot be used by the bacteria. Thirdly it causes ice crystals to form within the bacteria cells which can cause them to rupture – although only some of the bacterial cells will be destroyed. Freezing can help with the removal of water. Fish or meat that has been frozen will undergo some internal cell rupturing (though this usually does not affect the end product) and will result in approximately a 3% loss of water upon thawing. Freezing can also be used to control parasites and flukes in fish that is to be eaten raw. Flukes require to remain frozen at -20 C for 7 days (or -35 C for 15 hours) in order to be killed. Smoking Smoke adds flavour and is both a mild antimicrobial and antioxidant, but since it does not actually penetrate far into meat or fish is insufficient alone for preserving food. When smoking food the smoke is really there for flavouring, however the smoking process can play an important role in the removal of water. The process and effects of curing Examples of different foods and the usual cure methods Type of food Cure/preserving methods Expected shelf life Traditional Smoked Salmon Dehydration Salt Smoke 10 days at 4 C Immersion cured bacon Salt Nitrite Smoke (opt) 14 days at 4 C (unsliced) 1 week when sliced Dry cure bacon Dehydration Salt Nitrite Smoke (opt) 60 days at 4 C (unsliced) 1 week when sliced Hard/Dry Sausage Dehydration Salt Nitrite Nitrate Smoke (opt) Surface mould Whole, 6 weeks in pantry; indefinitely in refrigerator. 3 weeks when cut Salami style sausage Dehydration Salt Nitrite Nitrate Lactobacillus Surface mould Whole, 6 weeks in pantry; indefinitely in refrigerator. 3 weeks when cut Meat or fish Jerky Dehydration Salt Heat Nitrite (opt) Home produced – 1 to 2 months Commercially packaged - 12 months Country (Parma) style ham Dehydration Salt Nitrite Nitrate Whole, uncut ham can be stored safely at room temperature for up to 1 year. The ham is safe after 1 year, but the quality may suffer. Chutney Reducing water Reducing pH Excluding oxygen Unopened, up to 2 years at room temperature 4 weeks once opened Jam Reducing water Sugar Reducing pH Excluding oxygen Unopened, up to 2 years at room temperature Up to 3 months once opened and refrigerated Fermented vegetables Salt Reducing pH (by fermentation) Heat Excluding oxygen 4 months if not boiled, 18 months if boiled.
  8. To begin the Smokevember month here is an explanation of the roles of the different processes used in curing and preserving. Everyone who cures, smokes or preserves food will use a combination of these methods, often without realising why. When you first begin curing food it can be quite stressful to know whether, what you have just created, is safe for you or your family to eat. However, with even a basic understanding of what you are doing will help you to eat with confidence. The saying "If in doubt chuck it out" is generally good advice, however this can often lead to food that is perfectly safe to eat being thrown away. Fitstly, the more you understand about the processes the less doubt you will have and therefore the less that will be "chucked". Secondly, there are a lot of people who cure and preserve food regularly who are here and can offer you advice. I would therefore recommend that the advice be updated to "If in doubt ASK before you chuck it out" What is curing when applied to food? Curing is a method of preserving food to prevent spoilage. It refers to various preservation and flavouring processes, especially of meat or fish. Spoilage can be prevented (or delayed) by using several processes. Most curing processes involve applying a combination of these to achieve the desired taste, texture and storage time. Sometimes the extended storage time is only measured in days (as in traditional smoked salmon), weeks (as in dry cure bacon) or months/years (as in jerky, salamis and Palma/Country style hams) The different processes that can be used in combination: Reducing available water – including dehydration The growth of bacteria and bacterial spores is significantly affected by the availability of water in their surroundings. Water is also required by the natural enzymes in foods that cause autolysis – the self-destruction of cells by their own enzymes. If the water is removed or made unavailable, the storage life of most foods will be prolonged. Although we could totally remove the water from the food to have the preservative effect, it only really needs it be made unavailable to the spoilage organisms/enzymes. This can be done though several different processes. Removing the water – This is often achieved by warming the food in a relatively dry environment which enables the water in the food to evaporate. The smoking process is a good example of this, where the air that includes the smoke passes across the surface of the food causing the water to evaporate and pass out of the chamber with the smoke. This is why is us usually important to maintain good air flow through your smoker when cold smoking. Changing the state of the water – For bacteria to utilise water it must be in liquid form. One of the effects of placing food into a freezer is that it changes most of the water into ice and therefore make is unusable by bacteria. Freezing, however, does not remove liquid water completely as even when frozen some of the ice will be transitioning from solid to liquid and then back to solid. The lower the temperature in the freezer the less water there will be in liquid form at any point in time. Removing water from the bacteria cells – This is done by increasing the amount of salt and/or sugar around the bacteria, causing the water within their cells to be drawn out by a process called Osmosis. The removal of water from the cells prevents the bacteria from metabolising and growing and often results in their cell walls rupturing and the bacteria being destroyed. Binding the water – Various substances, including sugar, will chemically bind large quantities of water to their molecules and will therefore make it unavailable to the bacteria. This process is one of the important steps when making a BBQ sauce or ketchup that is not going to be eaten immediately. There is still water within the sauce so that it remains pourable, however much of it is bound to the sugars that are also present and which become more concentrated as the volume of the sauce is reduced through simmering. As you can see, you do not need to physically remove the water from the food to have a preservative effect - You just need to make it unavailable for any spoilage organisms to use. Jargon alert: The available water in food is known as Water Activity (aw) and to totally inhibit most spoilage bacteria and moulds an aw of 0.8 or below is required. Many commercial food processers will use an (aw) meter to check that their products are safe for long storage, however these are very expensive and are outside the pockets of most home curers. Even though most home curing processes will not achieve an (aw) of 0.8 or below, there will still be a preservative effect, though more limited, at higher (aw) levels. Increased Salinity – adding salt Salt is usually added in one of three ways – applying directly to the outside (Dry Brining), applying as a liquid solution (immersion brining or injecting), adding salt as an ingredient. There are several ways in which salt will inhibit microbial growth. The most notable is through osmosis, or dehydration (see above). Salt’s other antimicrobial mechanisms include interference with a microbe's enzyme activity and weakening the molecular structure of its DNA. When used as an effective bacterial inhibitor it requires salt solutions of ~10% to make most food spoilage organisms inactive, however salt at this concentration in our food would be unpalatable. Lower salt concentrations will also reduce bacterial growth but to a lesser extent. Many bacteria are very hardy organisms though and as salt concentrations fall the activity of many will again begin increase. The ways of applying salt through the differing curing methods will affect the storage time of the final product. A good example is the difference between Dry cured and Immersion cured bacon. Both methods can be used to produce an end product that contains 2.5% salt, however the resulting shelf life of both methods is very different. Unsliced Dry cure bacon can be safely stored refrigerated for up to 6 weeks whereas the equivalent safe storage life for immersion cured bacon is only 2 weeks. One of the reasons for this is the levels of salt that the bacteria are exposed to during the curing process. With Immersion cure bacon the levels of salt in curing solution will depend on the volume of immersion cure being used and the weight of the meat however it will usually not exceed twice the desired end concentration – therefore will rarely exceed 5% (and will frequently be lower when using larger volumes of cure solution). Although this will inhibit the growth of most bacteria it will not inhibit it completely. When Dry curing bacon you are applying crystalline salt directly onto the surface of the meat – where most of the bacteria will be present. As this salt dissolves in the water from within the meat it results in the surface bacteria being exposed to a saline solution of 100%. As the salt diffuses towards the middle of the meat this concentration will reduce however during normal curing times the surface brine concentration is unlikely to fall below 10% until the salt concentration in the meat is fully equilibrated. Another difference between the two curing methods is that the process of immersion curing will result in an increase in the water content of the meat by about 10%, whereas the process of dry curing will decrease the meat water content. Commercially the levels of salt in brining solution will be measured using a saline meter. These are fairly inexpensive and are often affordable by the home preserver. The electronic salt meters are best as they measure the salt through its ionic properties. Another common saline meter is an optical refractometer. These should ONLY be used for saline solutions that do not also contain sugars, as the presence of sugar will make the resulting "salt" readings highly inaccurate. Increasing sugar Sugar will have a similar osmotic effect on the bacteria cells as salt, causing them to dehydrate, however sugar molecules will also bind water molecules lowering the (aw) and making them unavailable for the bacteria to use. Sugar may also provide an indirect form of preservation by serving to accelerate accumulation of antimicrobial compounds from the growth of certain other organisms. Examples include the conversion of sugar to ethanol in wine by fermentative yeasts or the conversion of sugar to organic acids in sauerkraut by lactic acid bacteria. Increasing acidity (decreasing pH) Increasing the acidity of foods, either through fermentation or the addition of weak acids, has been used as a preservation method since ancient times. In their natural state, most foods such as meat, fish, and vegetables are slightly acidic while most fruits are moderately acidic. Only a few foods such as egg white are alkaline. Generally most food spoilage bacteria thrive within a narrow pH range and as you move away from this range they become increasingly inhibited. The effect differs though between organism. For example, a pH of 4.6 is sufficient to control most spore forming organisms (e.g. C. Botulinum) however a pH of 4.2 is required to control other vegetative pathogens (e.g. Salmonella). Increasing the acidity (reducing the pH) can be achieved in several different ways. The adding of an acid directly (e.g. Vinegar in sauces, pickles and chutneys), adding acidic fruit or juices (e.g. orange juice pH 4; lemon/lime juice pH 2; tomatoes pH 4.2) or adding a bacteria that increases the acidity of its environment as it grows (e.g. the use of a lactobacillus in salamis) Commercially the acidity levels are monitored by using a pH meter and these are inexpensive and can often be afforded by the home curer. Addition of Nitrite (and sometimes Nitrate) When added to foods such as cured meats, nitrite has at least three functions. Firstly, it contributes to the flavour - the nitrite is responsible for imparting the characteristic “bacon” flavour. Secondly, it reacts with myoglobin in the meat which gives the characteristic pink colour of cured meat. Thirdly, it inhibits the growth of food spoilage bacteria, most importantly Clostridium botulinum. The chemistry of nitrite when curing meat is quite complex and the exact mechanism by which it inhibits the growth of C. Botulinum is still a matter of scientific discussion. Nitrite is known to be effective at levels of less than 50mg per Kg of meat. Without laboratory analysis it is not possible to know with certainty how much of the nitrite remains in the meat following the curing process, as within the meat it will undergo a number of different reactions where it can remain free, be bound up byother molecules or cell components, it can be metabolised and broken down. Because of this the use of Nitrite in curing is actually calculated using “ingoing” amounts of Nitrite. Until a few years ago permitted Nitrite levels were ~350 mg/Kg (Ppm) however recently the EU, FSA and USDA have reduced the limits of ingoing nitrite to 150 mg/Kg (Ppm) for uncooked cured meat (and 100 mg/Kg for cooked meat). There are some exceptions for some traditional regional products where higher levels of Nitrite are permitted, however these exceptions limit the amount of residual nitrite in the meat which would have to be established through laboratory testing. As nitrite is gradually broken down in the food it will lose its effectiveness if time for controlling C. Botulinum. For foods that are stored chilled and have a short shelf life this is not a problem however for longer term storage (e.g. Parma/Country style hams and salami style sausages) Potassium Nitrate is also added. The nitrate does not play a direct role in the biological control but over time it is slowly broken down to form Nitrite, replacing the nitrite levels as they are lost. In the USA the use of Nitrate in bacon is no longer permitted as, when heated to high temperatures (e.g. when bacon is fried), the nitrates are converted to nitrosamines which have been linked to cancer in rats. In the UK the situation is less clear however the FSA stipulate that “The use of potassium and sodium nitrate is permitted only in non-heat-treated meat products, to a maximum amount added of 150 mg/kg”. Frying bacon before eating would be considered a heat treatment. Unfortunately, some of the manufacturers of ready-to-use cures (e.g. Supracure) have yet to change their usage instructions to comply with current regulations. When used at the recommended 5%, Supracure will result not only in an ingoing Nitrite level of >300 mg/Kg and will result in Nitrate being included in the bacon cure, but it will also produce a salt level of 5% which most people will find unpalatable. Exclusion of oxygen Preventing oxygen from reaching most bacteria will stop them from growing and increase the shelf life. This can be simply achieved by vacuum packing but can also be achieved by canning. The use of set sugar can also be used to form an oxygen barrier, as in jam. Care needs to be taken when excluding oxygen, as spore forming bacteria (e.g. C. Botulinum) require an oxygen free environment to produce their toxins. It is therefore important that food that is going to be stored this way should also have additional methods of spore control. This could be the use of added nitrite, by reducing the pH through pickling, or by suitable heat treatment. Heat treatment The only way to ensure that your food is effectively free of food spoilage organisms is to heat treat it, although this requires specialist equipment as some bacteria spores (e.g. C. Botulinum) are not killed by boiling water. At 120 C in a pressure cooker/canner (retort) it will take between 10 and 30 minutes kill the C. Botulinum depending on the acidity of the food. Chilling or Freezing The storage life of most foods can be extended by chilling or freezing. Although freezing would appear to be just an extension of chilling they actually work in different ways. The process of chilling food results in the slowing down of the metabolism of food spoilage organisms so that their effect is delayed. Even when chilled to 4 C they will still remain active and will eventually result in the food becoming unsafe to eat. The chilling effect is on both vegetative and spore forming bacteria. When stored at 4 C or below it will take C. Botulinum in excess of 10 days to produce levels of toxin that could begin to become hazardous to vulnerable individuals. The process of freezing works in three ways. Firstly, it continues to reduce the metabolism of the bacteria. Secondly it changes most of the available water to ice which cannot be used by the bacteria. Thirdly it causes ice crystals to form within the bacteria cells which can cause them to rupture – although only some of the bacterial cells will be destroyed. Freezing can help with the removal of water. Fish or meat that has been frozen will undergo some internal cell rupturing (though this usually does not affect the end product) and will result in approximately a 3% loss of water upon thawing. Freezing can also be used to control parasites and flukes in fish that is to be eaten raw. Flukes require to remain frozen at -20 C for 7 days (or -35 C for 15 hours) in order to be killed. Smoking Smoke adds flavour and is both a mild antimicrobial and antioxidant, but since it does not actually penetrate far into meat or fish is insufficient alone for preserving food. When smoking food the smoke is really there for flavouring, however the smoking process can play an important role in the removal of water. The process and effects of curing Examples of different foods and the usual cure methods Type of food Cure/preserving methods Expected shelf life Traditional Smoked Salmon Dehydration Salt Smoke 10 days at 4 C Immersion cured bacon Salt Nitrite Smoke (opt) 14 days at 4 C (unsliced) 1 week when sliced Dry cure bacon Dehydration Salt Nitrite Smoke (opt) 60 days at 4 C (unsliced) 1 week when sliced Hard/Dry Sausage Dehydration Salt Nitrite Nitrate Smoke (opt) Surface mould Whole, 6 weeks in pantry; indefinitely in refrigerator. 3 weeks when cut Salami style sausage Dehydration Salt Nitrite Nitrate Lactobacillus Surface mould Whole, 6 weeks in pantry; indefinitely in refrigerator. 3 weeks when cut Meat or fish Jerky Dehydration Salt Heat Nitrite (opt) Home produced – 1 to 2 months Commercially packaged - 12 months Country (Parma) style ham Dehydration Salt Nitrite Nitrate Whole, uncut ham can be stored safely at room temperature for up to 1 year. The ham is safe after 1 year, but the quality may suffer. Chutney Reducing water Reducing pH Excluding oxygen Unopened, up to 2 years at room temperature 4 weeks once opened Jam Reducing water Sugar Reducing pH Excluding oxygen Unopened, up to 2 years at room temperature Up to 3 months once opened and refrigerated Fermented vegetables Salt Reducing pH (by fermentation) Heat Excluding oxygen 4 months if not boiled, 18 months if boiled.
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