Fermented Sausages : Background – Control Theory
Includes Chuckwagon on Are “Fermentation Chambers” And “Curing Chambers” Really Necessary?
You can review the posts from the original Project “A” (135+ pages, divided into thirds ) by clicking one of the following:
Wisdom Gleaned from the Original Project “A” (part 1) (part 2) (part 3)
SECTION ONE – BACKGROUND – CONTROL THEORY
In order to make fermented sausages, we need a short introduction to the fermentation process. Chapter 6 of “The Art of Making Fermenting Sausages” covers that well. Up until now in our sausage making, we used the recipe to control the process. However, for fermented sausages, we will need to control temperature and humidity as well as the recipe. In order to control temperature/humidity, we rely on engineering practice. That is best illustrated by talking about fundamental control challenges. So, without further ado…
Early Temperature Control Problems
Practical temperature control for fermentation is similar to controlling temperature for the comfort of other living organisms, namely, people. It has always presented a fundamental challenge- – temperature can deviate both above and below a desired level.
For example, until recently, large buildings (especially older buildings) were able to provide adequate heating in the winter months and adequate cooling in the summer months. The problems came in spring and fall, when cool mornings give way to warm days. It was quite a chore to convert a Heating / Ventilating / Air Conditioning (HVAC) system from heating mode to air conditioning mode, so during the in-between days, ventilation (open windows) became the norm and the occupants got the chance of being too cold AND too hot on the same days.
HVAC engineers came up with a solution. They modified the system so they could run both the cooling AND the heating systems at the same time, then blend the air, on those awkward days. It was inefficient, but the systems were difficult to change over very quickly and this seemed to be the only adequate method. Today, it is less difficult to switch over, so that in some buildings, when heating is called for on the shaded side and cooling on the sunny side, individual room controls can heat or cool a given room from a common supply of air.
Home systems with central heating and air conditioning can be changed over “at the flick of a switch,” nowadays, with little trouble. The “next big thing,” though, is to have a “smart” thermostat decide when to automatically switch over.
Early versions of these thermostats (I remember a Carrier heat pump system built in the ‘90s) suffered from one problem: if you set cooling to come on at, say, temperatures above 72 degF and heating to come on at temperatures below 72, what happens RIGHT AT 72? Worse, what if cooling comes on at 71, and heating at 73? Answer: the heating and cooling systems will work against each other, cycling back and forth, each trying to overcome each other, which is obviously not good. The HVAC folks decided to force the equipment to recognize that the two functions needed to be separated by a small adjustable amount, often 2 degrees in house-sized HVAC equipment.
As long as the equipment is fairly responsive, it works well. However, the temperature can continue to coast downward after cooling cuts off, while the liquid refrigerant in the reservoir is evaporated. Likewise, if a large mass of material is heated up, the excess heat accumulated in the mass has to cool down by heating the surrounding air, until the excess is used up. Minimizing system mass and reservoir volume helps but, as you will see, there is still a two- to five-degree range in which your system will have to operate.
This functionality is becoming more and more popular. The inefficiency is the price you pay for comfort and flexibility. Good design means minimizing this inefficiency.
Split Range Temperature Control
The control system we described above is called “split range” control. Below a certain setting, one system tries to raise the measured value. Above a certain slightly higher setting, a different system tries to lower the measured value. It’s sometimes complicated, and requires two different but integrated systems, but when properly tuned, it works well. In my own field, chemical manufacturing, split range systems to control distillation column pressure are very common. Below the desired pressure, a valve is opened by a small amount, introducing inert gas into the distillation column. This way, pressure is controlled by the process itself, by blanketing a heat exchanger called the condenser, making it less efficient. Less condensing means the pressure will rise. Conversely, pressure is decreased by venting the inert gas, allowing the condenser to become more efficient.
Pressure systems move rapidly, compared with temperature systems. Humidity systems move even more slowly. So, how does this impact fermenting/curing chambers? Suppose you need to want to control the temperature to 75 degF. It’s a warm summer day, and the internal temperature soon climbs to 76 degrees. A line voltage thermostat switch turns on the refrigerator, which begins to cool. There is always a lag due to “thermal inertia”- – the sausages, the internals of the refrigerator, the air all retain heat, some of which must be removed. So the refrigerator compressor runs until temperature drops below 75 or so (depending on how good the instrument is and what “offset” is built into it), and the temperature switch stops the compressor.
This cycle continues until the day cools off, at which point the temperature drops below, say, 73 degrees, at which point the problem changes entirely! Instead of cooling, the controls must now heat the system.
A small heater switches on. It warms the sausages, air, walls, etc. until the temperature rises above, say, 74 degrees and it switches off. This cycle continues through the night and into the next day, at which time it swaps over to cooling mode again.
Suppose it stays cool. The heating portion of the cycle will continue to operate. Suppose it stays warm. The cooling portion of the cycle will continue to operate. It’s those in-between times when there is potential for the two to fight each other that you have to be careful of, and you must “tune them out” by widening the temperature difference between the two, which is called the “dead band.”
Clear as mud, huh? Well, if you pick the right time of the year for your first batch of salami, maybe you can get away with heating only, or cooling only. I wouldn’t count on it, though, so let’s build something better.
The traditional Armenian pastrami, or pastirma, is made with almost complete reliance on natural seasonal conditions. (The Eastern European evolution of what is called pastrami in Jewish delicatessens has evolved in a slightly different direction, and is made differently nowadays.) A Turkish friend of mine tells me that the Armenians still do it this way. In the fall, the temperature drops. People hang beef up, let it naturally ferment for a week or ten days, by which time the temperature drops ten or more degrees, cutting back on bad bacterial action, and the beef dries to a desired level.
However, problems occur when there’s a weather condition which we in the West call “Indian Summer” (a prolonged period of warm weather following a freeze). Turks call it a “Pastrami summer” instead, because it plays havoc with Armenian pastirma production. This can be viewed as a fundamental process control problem, one in which the traditional “work around” works most times but sometimes goes badly. …frequently enough that it has entered folklore. Fortunately, we can build some simple equipment that allows us to avoid the problem.
(to be continued…)
Chuckwagon on Building a Chamber:
From the first Project “A” comes this item on refrigerators, with Ross Hill:
Posted: Thu Jun 09, 2011 09:27
I have a refrigerator that is used for overflow food storage and I can adjust the thermostat for most any temperature. It is frost free so the humidity is always very low. My house is air conditioned and kept below 80 degrees F. What am I lacking?
Ross, your refrigerator might not work for a curing chamber as it may need to be kept warmer than the controls are designed to keep it. Also, we need to raise the relative humidity rather than keep it low. You would have to disconnect the frost-free mechanism. How about reading the material found at the bottom of this article, titled Are “Fermentation Chambers” And “Curing Chambers” Really Necessary?
As you are a craftsman, you may wish to build a box of plywood and line it with thick-gauge plastic sheeting. You may possibly be able to place a pan of salt and water in the bottom to produce enough humidity to support fermentation. It will be necessary to also heat the box slightly, using some type of heater – perhaps a slow-cooker heating unit or an aquarium heater. We’ll cross that bridge in a few days. Can you give me an idea how much relative humidity you have where you live?
I’ll assume here that you already have (or will purchase) a used refrigerator. We’ll be working on our project well into warmer weather (in the northern hemisphere), and they’re inexpensive. (Mine cost $35.) However, if you live in a cool climate, feel free to build your own cabinet. We will operate at 20 degC/68 degF for a few days, then at 14 degC/57 degF for two or so months. It’s easy to rig up an incandescent light fixture or soldering iron for heat. Cooling is a little tougher unless you use a refrigerator.
Split Range Humidity Control:
Temperature split range control is straightforward (see above). Humidity split range control is more complicated. Let’s have a look at this similar but slightly more complicated problem, compared with temperature control.
There is always heat leakage into, or out of, the chamber. The temperature inside the chamber can be either (1) hotter than desired, or (2) colder than desired. Likewise the humidity inside the chamber can be either (1) more than desired, or (2) less than desired, but there’s a complicating factor- – water can be introduced into the chamber by means of makeup air, which can be higher or lower than the desired level. Note that water is NOT generated by fermentation. Lactic acid is the product of the fermentation reaction, starting out fast, then tapering off. This is responsible for the rapid “nosedive” in pH.
Water is introduced with the meat. The water content of meat, often estimated as 75% water, may be higher if additional water is injected by the meat packer. A portion of this water must be removed from the sausage (lowering the water activity, Aw) in order to inhibit microbiological activity. There is always water evolution from inside the chamber, although its rate of evolution varies with time- – higher at first, tailing off toward (but never quite reaching) zero. The rate of water removal must be carefully slowed, controlled to a high humidity level, to avoid “case hardening,” where the outer layer of the sausage becomes too dry too soon and is almost impervious to water diffusion outward from the sausage into the air. So, how do you remove the water at a regulated rate?
Obvious first answer- – vent the air from inside the chamber, removing moisture, and make up with outside air. But what if the outside air is more humid than the inside air? …or what if you are just starting fermentation?
We introduce the concept of a balance, here. For maintaining a steady temperature:
heat added – heat removed + heat generated + heat accumulated = zero
with the consequence that, if the heat flowing in and out didn’t equal each other, heat would accumulate and the temperature would change. (Heat effects of the fermentation reaction can be ignored. They’re pretty small.)
Heat can be added by leakage in through the sides of the chamber, or by turning on a heater. Heat can be removed by leakage out through the sides of the chamber, or by turning on the chamber’s refrigeration system.
For maintaining a steady humidity:
water added – water removed + water generated + water accumulated = zero
The equation always adds up to zero, so without removing water somehow, the meats will remain too wet, to the delight of spoilage bacteria. If too much water is removed, the meat will dry up. (Jerky, anyone?)
Water can be added by adding humidified air (as long as the makeup air is more humid than the vented air), or by using a humidifier. Water can be removed by venting water-laden air, as long as the makeup air that replaces it is less humid than the vented air. You can get into trouble two ways- – too wet (if you need to get rid of water and the outside air is too humid), or too dry (if you need to add water and the outside air is too dry.) The consequence of the air being too dry is the evaporation rate from your meats being too high, which will lead to “case hardening.”
Think of the humidity difference between the environment inside the sausage and the environment outside the sausage as a driving force: the bigger the difference, the bigger the driving force and therefore, the faster the rate of moisture movement. …also, note that if the environment outside the sausage is too wet, water will go INTO the sausage, whereas if the environment outside the sausage is too dry, water will move outside, the bigger the difference, the faster. At this stage, you could get highly technical and dive into the mathematics. Let’s not do that, please. Instead, just remember that we want the humidity difference to be “just right” as specified by those “wise guys (and gals) who know better than we, and they have both tradition and experience on their side. Fortunately, they believe in sharing, and have written it down in recipes. We’ll follow the recipes, thank you.
Okay- – group hug, a couple of choruses of Kumbaya, enough of the theory, and let’s get on with how to control temperature and humidity.
Control System Requirements:
At this stage, let’s look at the requirements. Your temperature and humidity targets are as follows (for Project “A” salami):
• Ferment at 68˚ F. (20˚ C.) for 72 hours, in 85% to 90% humidity, using T-SPX bacteria..
• Spray with “Mold-600” mold. Dry at 57˚ F. (14˚ C.) in 80-85% humidity for 2 to 3 months (until 30-35% weight loss is achieved).
• Store at 55˚ F +/- 4 degrees. (13˚ C.) in 75% humidity.
Several options come to mind. There’s a process control solution, feeding back a control signal to a humidifier if outside air is dry, as for example, in the desert Southwest. It may involve drying the inlet air if outside air is humid, such as on the Gulf Coast. In most climates, it may require both at one time or another. The usual condition is for the air in the chamber to start off too dry, then become too humid as water evaporates from the meat and accumulates in the chamber. We would like to control both conditions.
For small operations, there is a cheaper, more stable method. This one, advocated by many people including Chuckwagon in his Summer Sausage recipe, exploits the physical properties of salts, and uses a bed of rock salt to fix the humidity at close to 75% over a surprising range of temperatures. Exposing your fermenting/curing chamber to a bed of rock salt (good ol’ sodium chloride, NaCl) wetted with water fixes the humidity. Excess water evaporating from the meat drives the humidity above 75%, so you need to vent that excess water occasionally, to maintain humidity control. (Note that case hardening was a problem during the original Project A. This may be the reason- – people were “dumping” water too often, and the lowered humidity “driving force” caused evaporation rate to be too high.) The water pan actually will take care of that extra water. Amazing! (…that is, unless there’s a large pool of water condensing on the insides of your chamber. …but more about that later.)
As for maintaining the 85% humidity, there is a similar non-toxic salt which you can use- – the “light salt” sold in most grocery stores which became widely available when the “low salt” food craze hit the market, a few decades ago. Technically, it’s known as potassium chloride or KCl.
In an article named “Humidity Fixed Points of Binary Saturated Aqueous Solutions,” which you can find at http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.333.7394&rep=rep1&type=pdf you will find a compilation and regression analysis of 28 different combinations of various types of inorganic salt-and-water. Ideally we can find a non-toxic salt which will give the desired humidity, and this is indeed the case:
• Without a salt present, water provides 100% humidity, which varies with temperature.
• Potassium chloride (marketed as “light salt,” a salt replacer, available at most grocery stores) fixes humidity at 88.6% (0 degC, 32 degF) to 84.3% (30 degC, 86 degF). At 68 degF (20 degC) fermentation conditions, it fixes humidity at 85.3%. At 14 degC drying conditions, it fixes humidity at 85.9%. Therefore, potassium chloride appears to be ideal for salami fermenting needs.
• Sodium chloride (table salt) fixes humidity at 75.5% at 0 degC, going down only a little bit to 75.1% at 30. It could be used for storage.
However, vacuum packed storage is probably a better answer.
Our ol’ buddy Shuswap reminds me to include some words on storage. At issue, the requirement “Store at 55˚ F +/- 4 degrees. (13˚ C.) in 75% humidity. “ Here’s an excerpt from a “three-way” exchange between him, me, and Chuckwagon, heavily redacted by the CIA or the DVD or the Sausage Police or somebody:
Hey, hey, Phil! How are you sir? I’ve got El DuckO at my house for a week and we’re having a ball…
- A cool basement is the place to store the pepperoni…
- If we vacuum pack the stuff when it is at 75%, then the humidity is a “moot point”…
- … in Cuba, they push the sausages down into a can of lard to keep it moist.
- … a tray of salt will produce about 75% humidity. Do you have a cold, damp, cellar there in B.C.?
P.S. Hi, Phil. Duck here.
The idea on vacuum packing is that the sausage, which is already at close to water equilibrium conditions, gets packed in a container (vacuumed bag) where the water has little room to expand, so it stabilizes pretty close to the same humidity that it had. As to temperature, it’s probably not sensitive.
Traditionally,,,[sausages] were stored in cellars at moderate temperatures, but you can stash them [vacuum-packed] in the refrigerator with no adverse effect. …except that they’re visible, and therefore subject to being eaten by …“others.”
Are “Fermentation Chambers” And “Curing Chambers” Really Necessary?
Posted: Mon Jan 10, 2011 04:43 by “Chuckwagon”
Yes, they are. Have you ever cut into a salami and found a gray ring around red meat? This condition occurs when the humidity has been too low during curing, causing quick dehydration (and thus hardening) of the casings – not allowing the correct amount of moisture to naturally dissipate from the sausage as it cures. Trapped moisture can also cause the sausage to spoil. Ol’ Rytek Kutas used to compare case hardening to stuffing a pipe full of sausage. He said, “When the ends of the pipe are welded shut, there is just no way for the moisture to escape from the sausage”.
It is important to understand there are two atmospheric conditions that we must be able to control if we are to produce dry-cured sausage. They are simply (a.) temperature and (b.) humidity. For fermenting sausage, the ideal temperature range is between 40° F. and 55° F. (4° C. and 13° C.), while maintaining a relative humidity of about 70%, depending upon the sausage being made. Inside a typical refrigerator, the humidity is only about 30% to 40% – much lower than that needed to cure sausages. Many people have tried to maintain 70% humidity by placing a pound of salt into a shallow pan of water. Although, the humidity indeed increases, this method is not recommended as it is not easily regulated or controlled. [Ed. Note: We will use a variation of this, using potassium chloride (“lite” salt) instead of sodium chloride (“table” salt). Depending on the size of your chamber, this may be a better answer.]
Again, dry-cured sausages at the outset need more than 70% relative humidity to start the fermentation process and keep them from drying too quickly. For the first few days (depending upon each recipe), they are placed into a controlled, heated, and moist fermentation chamber to promote fermentation through the development of any number of strains of lactobacilli or pediococci (lactic acid producing) bacteria. Directly responsible for fermentation, the bacteria consume sugar and produce lactic acid, giving the sausage a sour, tangy, taste. The more sugar added, the more “tangy-tasting” the sausage becomes.
Hey! Did you notice I used the word taste – not flavor. Actual flavor-producing bacteria are another strain altogether. Later in the process, the humidity and temperature are usually lowered a bit as they are placed into a “curing chamber” for further slow, controlled dehydration. In dry climates particularly, sausages must be cured inside a chamber capable of sustaining a high degree of moisture at varying temperatures. Typically, different “holding periods” are required for dry-cured sausages in an environment of 70 – 75% relative humidity at assorted lower temperatures specified by individual recipes, although the greatest fermentation takes place between 100°F. (38°C.) and 110°F. (43°C.).
Without fermentation and curing chambers, your sausage will probably spoil. Professional chambers or rooms may cost thousands of dollars – not an investment all hobbyists are willing to make. However, using a little imagination and applying a bit of skill, many people transform old refrigerators or freezers into top-quality curing chambers. Some sort of humidifier/dehumidifier with an exterior control must be employed to effectively produce top-quality, fermented sausages, and hobbyists have come up with every sort of contraption imaginable; many are first-rate! As I was in the piano building business for nearly half a century, for decades, I effectively used a DamppChaser™ piano humidifier/dehumidifier system, that I incorporated into a modern refrigerator with all sorts of added shelving and hangers provided for stocking meat sausages. If you prepare dry-cured, smoked, fermented sausages, bacon, or ham, you must:
1. Purchase a reliable thermometer for constantly monitoring the dry-curing temperature.
2. Purchase a hygrometer for monitoring relative humidity.
3. Build or use some type of “fermentation chamber” (described below)
4. Build or use some type of “curing chamber” (or drying room) having controlled specific relative humidity for a specified time period.
5. Install a means of controlling the temperature and controlling the relative humidity in your fermentation chamber as well as your curing chamber.
6. Provide for a “storage chamber” or storage room for long-term storage if necessary.
So, what is the bottom line? A small humidifier (use only distilled water please) and an in-line voltage humidistat (which senses relative humidity, operating on the same principle in which we control temperature) must be purchased. [Ed. Note: In dry climates, this may be true. However, in locations near water, more likely de-humidification will be needed. In fact, during early parts of the first Project “A”, most participants had to open the door of their chamber daily to vent water vapor. …which, don’t get me wrong, is entirely “fair.” Just don’t overdo it.]
An effective method for heating and cooling the chamber becomes necessary and a “single-stage, line-voltage thermostat” does the trick, alternately controlling a small ceramic heater and a cooling fan. Mine came complete with a temperature sensor, a temperature control with a relay switch, and instructions. The line voltage thermostat solved the problem of having the refrigerator’s controls limiting the operational temperature from only 32°F. (0°C.) to 40°F. (4°C.). In total, I spent a bit more than I perhaps should have, but I purchased first class controls and equipment with ability to control a wider range of temperatures and humidity. Later, I changed the “single stage thermostat” for a “two-stage line voltage thermostat”, enabling me to control two independent devices – such as the ceramic heater and a computer fan (used for cooling) or even a small cooler. The two-stage unit is more expensive, but may be just the item you are looking for. For smaller operations, the proper thermostat could be as near as your local pet supply store where reptile terrariums are found. If you wish to incorporate ultimate convenience, a “two-stage line voltage thermostat” may be just the device you require. Nutone makes a model, and Green Air (www.greenair.com) yet another.
If you are not inclined to develop your own temperature and humidity controls, search sausage-making supply catalogs that provide them pre-built and ready to simply plug in. The Sausagemaker in Buffalo, New York, offers top quality controls and humidifiers, as do other suppliers. Quality controls for monitoring temperature and humidity may seem pricey, but their reliability is critical and you really wouldn’t want to purchase a second-rate product that will break down in time. Some models even have all the controls contained in a single handy unit. The publication “The Art Of Making Fermented Sausages” by Stanley Marianski, includes much information as well as some great ideas for building and equipping your own fermentation and storage chambers. Mr. Marianski has even included a few sources for ordering supplies over the internet. For the true “do-it-yourselfer”, there are also some great plans available from Phil Young, a moderator called “Wheels”, at sausagmaking.org. “Wheels” has published them on the site’s bulletin board free of charge.
At the beginning of the fermentation process, some sort of fan must be used to carry away moist, stale air as the sausage dries. The moisture content is at its highest as the process begins, although it usually only requires a smaller computer fan to move air away at about 2 miles per hour. [Ed.Note: See a later discussion on boundary layers. The function talked about here is mixing the air in the chamber. This sounds mysterious at the moment?? It will become clearer, shortly.] Halfway through the process, depending upon how much moisture is being dissipated, the air speed may be safely decreased to only about one mile per hour. Without this minimal draft being provided, the moisture collecting on the surface of the sausage could become slimy, promoting the growth of unwanted microorganisms. If moisture continues to collect on the surface, the relative humidity must be lowered slightly. The ideal device is a sturdy computer fan, capable of continuous operation. A vast array of them is available at your nearest computer supply store.
Best wishes, Chuckwagon
Things to come:
In the next post, we’ll go into some specifics. Specifically, we’ll design and build a fermenting/curing chamber using a small “dorm” refrigerator, a “two-stage” temperature controller, and a “two-stage” humidity controller, the whole shebang for less than $100 USD. You might go ahead and find a used refrigerator, plus (maybe the tougher task, if your spouse is like mine) a place to put it.
This finishes our section titled
SECTION ONE – BACKGROUND – CONTROL THEORY