Smoking Meats and Humidity Control

When smoking meats in a smokehouse, or preparing sausages in the kitchen, we should know how to control humidity. The humidity and temperature control is of utmost importance when smoking salmon. When making dry sausages the salting and moisture removal are two main methods of meat preservation. We must eliminate as much moisture as possible since the moisture is the main culprit that spoils the meat. We can employ fans blowing hot air at the sausages, but this will immediately harden the surface area of the meat and will create a barrier that will trap moisture inside. The sausage will be dry on the outside but raw and moist inside. Cold smoked or air dried sausages are processed at the beginning at very high humidity levels and low temperatures. Low temperatures prevent bacteria growth and high humidity allows for slow moisture removal without hardening the surface of the sausage. By controlling humidity (moisture in the air) we can create proper conditions for drying and smoking products at different temperatures. When cutting meats we don't want moisture to condense on knives, stainless steel tables or even walls as this will help bacteria to multiply and will shorten the useful life of the product.

Humidity or better said the "relative humidity" defines how much water (vapor) is present in the air at a particular temperature. In technical terms the relative humidity is the percentage of moisture air is holding compared to the maximum moisture it can hold. The air almost always contains some water vapor and although we don't see it, it is there and it has a certain mass (weight). This amount of moisture will greatly depend on a climate in which a person lives. There is always more humidity in areas rich with bodies of water, like lakes, rivers or the sea shore. Arid areas like deserts or mountains have less rivers and lakes and subsequently less humidity. In hot weather when humidity is also high, we feel even hotter than it is. The reason being that by perspiring, (removing moisture) our body cools us and provides a relief. If the humidity is high outside our perspiration has nowhere to go and we sweat even in the shade.

The air at certain temperatures is capable of holding a fixed amount of moisture in it. The higher the temperature the more water can be held by air and vice versa.  As the amount of moisture in the air is fixed for at least some time (the clouds can bring moisture and rain), raising the temperature lowers the relative humidity. There is a point for each temperature reading when the air can hold the maximum possible amount of water and we call it a saturation or a dew point. At this point the relative humidity is 100%. If the dew point is below freezing, it is called the frost point and the water vapor will form the frost or the snow. Air with a relative humidity of 50% contains half of the maximum moisture it could hold. If the room is at 100% humidity and we spilled a bucket of water on the floor, this water will never evaporate as the air can not absorb it anymore. The only solution is to wipe it off or raise the temperature of the room what will lower the relative humidity and the air will be able to hold more moisture. Keep in mind that in a confined room  we can adjust relative humidity by increasing/decreasing temperatures, nevertheless, the mass/weight of moisture remains the same. In order to change this amount of water we will have to either remove some of it using dehumidifier or bring more of it into the room (humidifier, placing a water dish on a heater, boiling a kettle etc). Note that a reading of 100% relative humidity means that the air is totally saturated with moisture, creating a chance of rain. This does not mean that we only get the rain when humidity on the ground is 100%. To get the rain the relative humidity must be 100% where the clouds are forming, but the relative humidity near the ground could be much less.

You can see in the following table how much water vapor can be held by air at different temperatures:

In the same room at 100% relative humidity, if we suddenly lower the temperature, the air can now hold less moisture and the droplets of water will start condensing on smooth surfaces like mirrors, knives, or even meat itself. You may say that the water is coming out of the air and it is almost like raining. This phenomenon can easily be observed in hot climates for example in Florida. In the early morning (6 AM) when the temperature is low, there is so much humidity that there is water all over the car: tthe mirrors, the glass and all over the body. The roof of the house is so wet that the water is dripping down. It is impossible to cut the wet grass as the mower will keep on stalling. We are at 100% relative humidity, the saturation. Then the sun gets up, the temperature starts to raise and the moisture goes back into the air. After a few hours everything is dry again and the grass can now be cut with the machine.

 

To see how the temperature affects humidity in real life, we have taken hourly readings of the temperature and relative humidity  in Florida on November 10/11, 2006. The resulting table and the chart follow below:

As documented on the graph, there was a steep rise in humidity levels (from 60 to 90%) when the temperature dropped from 70° F (6 PM) to 62° F (11 PM). These high humidity levels continued until 7 AM. Those would be the best humidity levels for cold smoking. The fire should be kept very low in order not to increase the temperature too much. Then during the day the product should be placed in a cooler at 85% humidity levels. At 7 PM the same product would be taken from the cooler and cold smoked again.

 There was a big drop in humidity levels from 90 to 36%, when the temperature increased from 60° (7AM) to 77° F (12 AM-noon). Also at 7 AM there was so much humidity that there was a fog all over the area which disappeared completely one hour later.

7 AM - fog - 90% humidity	8 AM - clear - 84% humidity

Note: The above chart proves that the cold smoked products can be produced from the middle of November to February, even in a hot Floridian climate, as long as we pay attention to the time of smoking, the temperature and the humidity levels.

 Smokehouse and Humidity

There are some expensive factory made smokehouses that permit humidity control. Most smaller factory made smokehouses cannot even produce cold smoke and humidity control is out of the question. Regulating humidity in a home made smokehouse can be done indirectly, and is relatively simple and cost free. What is required is a fair understanding of a smoking process and humidity behavior.

A particular climate and ambient temperature are the most important factors that a sausagemaker must learn how to manipulate. Thus when smoking in a home made smokehouse the humidity can be controlled by:

• choosing the time of the smoking

• placing a water filled pan inside the smoker

• using moist wood chips or sawdust

The amount of needed humidity is dictated by:

• type of a product - hot smoked sausage, cold smoked sausage, smoked and air-dried ham, or just air-dried ham

• the smoking method that will be employed - cold smoking, hot smoking

Geographical location plays a crucial role here. There is  more humidity in areas containing a lot of water like lakes, rivers or the sea shore. Arid areas like deserts or mountains  have less water and subsequently less humidity. If you live in the Eastern part of the USA or Gulf states, you have a lot of humidity. If you live in the West (Arizona, New Mexico, California) you get less of it. As you cannot change the physical location of the smokehouse, you have to learn how to go around it and how to choose the time of smoking to your maximum advantage.

The most important rule to remember that when the temperature goes up, the humidity goes down. When the temperature goes down, the humidity goes up (night). That holds true when the weather is relatively stable or when smoking inside. When the clouds come in and it starts to drizzle, the humidity will go up immediately.

Different smoking methods require different humidity levels:

• cold smoking -  75 - 85 %. It is important to employ high humidity levels when cold smoking.

• warm smoking - 50 - 70 %. It is advisable to start smoking at high humidity levels.

• hot smoking - 40 - 50 %. In case of hot smoking which is a relatively short process (about 2 hours), humidity control is of secondary importance.

In dry climates like New Mexico or Arizona the relative humidity stays  low at 15 - 20 % during day time and it will not be advisible to smoke meats at such conditions. The meat will prematurely dry out. The remedy will be to place a water pan inside of the smoker and moist wood chips. The best solution is to smoke at night time when the temperature will drop and the humidity will increase.

An often heard complaint when smoking in outside smokehouses is that the meat is wet on the surface and the final product tastes sour. In most cases it is a humidity problem. Outside smokers in most cases have a free standing firebox that is connected to a smoker by a digged in trench or pipe (clay or metal). After rain the ground is soaked wet and this moisture will travel with smoke together. The remedy is to heat up the smokehouse well so that the moisture will evaporate away. Another problem is that when smoking in a popular metal drum at  very low temperatures there might be a case that the smokehouse temperature will be lower than the temperature of the entering smoke. Moisture from the outside or even moisture from the wood or the meat itself will condense on the walls of the drum. Then it will combine with soot and other unburnt particles and will start condensing on the meat or sausages. That of course will affect the color of the product and even worse, it will impart a soury flavor to the finished product. The solution is to insulate the drum on the outside with some material and heat up the drum before smoking.

Note: controlling humidity levels is very important for commercial manufacturers who produce thousands of sausages a day. Proper humidity control during production and storage will decrease meat loss and will increase profits. It is of lesser importance for a home sausagemaker unless he is making fermented sausages.

Manufacturers of humidity sensors that could be inserted into a smokehouse can be located  on the Internet although the prices are rather steep.

On the other hand indoor/outdoor humidity meters are reasonably priced. For a home made system the most economical way to go will be the dry bulb and the wet bulb system like the one below:

Before the reading is taken the muslin bag that covers bulb of the wet bulb thermometer must be moistened by dripping it in clean water. Then the thermometer is inserted into the smokehouse and after about 30 - 60 seconds the reading is taken. At the same time the temperature of the dry bulb thermometer is also taken and the difference from both readings is obtained. Then the table is consulted to determine the relative humidity. This procedure is explained in details below in the Dry and Wet Bulb Method. The thermometers should be placed horizontally on the same level. If they were placed vertically with the wet bulb thermometer below the dry bulb thermometer, we could obtained incorrect readings as the smoke and air would be cooled by the evaporation of moisture on the wet bulb. It can easily be determined from the wet bulb and the dry bulb tables that the flow speed of the smoke will influence the reading. The slower the flow rate of the smoke, the smaller the difference in temperatures and the higher the relative humidity. The faster smoke flow, the lower relative humidity and the faster drying (moisture removal) from the smoked product.

Sausage Making and Humidity Control

Moisture (humidity) control is of utmost importance in meat processing facilities. Any moisture that will show on meats as water droplets will create perfect conditions for the development of bacteria. The products will also feel "slimey". The recommended humidity levels for meat processing rooms are:

• meat cutting room    -    45 - 60% relative humidity at 10° - 12° C (50 - 54° F)

• coolers                    -    85 - 95% relative humidity at 0° - 4° C (32 - 36° F)

In coolers the higher humidity is required to prevent the drying of the meat products as that will lead to weight loss and cut in profits. The humidity control in a meat plant is based on dew point control. Dew point is the temperature at which condensation forms. When air comes in contact with a surface (often metal or glass surfaces) that is at or below its Dew Point temperature, condensation will form on that surface. In a meat plant the item that is at risk is meat taken out from the cooler as its temperature will be about 2° C (35° F). In the processing room the temperatures are about 10° - 12° C, though they may reach even up to 16° C (60° F) if the meat will not remain there longer than one hour. By adjusting the room temperature and its humidity levels we can control the temperature of the dew point.

In a well designed meat plant the temperature will stay more or less the same. If the facility is climate controlled the amount of relative humidity should also remain at the same level. The meat taken out of the cooler for processing should also have the same temperature. In the kind of "improvised" facility without automatic control the relative humidity can be controlled by any of the following factors:

• meat temperature - the worst solution as the meat's temperature will have to be increased which will lead to bacteria growth and shorter shelf life of the product

• room temperature - will have to be lowered which is acceptable in a cutting and processing room. Bad idea in coolers where air dried and fermented sausages must be kept for a long time at precise temperatures and humidity.

• room humidity - the best idea as it allows moisture removal (dehumidifier) or moisture introduction (humidifier) by separate devices. Those simple units will control the relative humidity without the need for room temperature adjustments or worrying about meat temperature.

It is very unlikely that a home sausagemaker will ever bother with humidity control but for those interested the following table will show how it is done. Only a part of the table that contains temperatures that might be encountered in a meat processing facility is quoted. Tables that include all temperature and humidity readings can be obtained on the Internet.

Dew Point Table in ° F

 

Air Temp. in °F	% Relative Humidity
	100	95	90	85	80	75	70	65	60	55	50	45	40	35	30	25	20	15	10
65	65	63	62	60	59	57	55	53	50	48	45	42	40	36	32
60	60	58	57	55	53	52	50	48	45	43	41	38	35	32
55	55	53	52	50	49	47	45	43	40	38	36	33	32
53	53	52	50	48	46	44	43	41	39	37	35	32
52	52	50	48	46	44	44	43	41	37	35	33	32
50	50	48	46	44	44	43	39	37	35	34	32
45	45	43	43	39	39	37	35	34	32
40	40	39	37	35	34	32
35	35	34	32
32	32

Note: numbers in red color denote the Dew Point. For example if the temperature in the sausage factory is 60° F (16° C) and the relative humidity is 50%, the intersection of the two shows that the Dew Point is reached at the temperature of 41°F (5° C), or below. This means that the moisture that is present in the air at 60° F (16° C) will condense on any surface that is at or below the Dew Point temperature of 41° F (5° C). This also means that if the meat having a temperature of 35° F (2° C) was brought from the cooler into this room (60° F,  16° C) the moisture would condense on its surface. The meat's temperature of 35° F (2° C) is below the Dew Point limit of 41° F (5° C).

If the meat's temperature (35° F, 2° C) and room's humidity (50 %) remain constant, the only way to correct the problem will be to lower the room's temperature to 52° F (11° C). At the intersection of  air temperature of 52° F (11° C) and 50 % relative humidity the Dew Point becomes 33° F (0.5° C) which is below meat's temperature of 35° F (2° C).

If we decide not to change the room temperature and leave the meat temperature at 35° F (2° C) the only way to correct the problem would be to lower relative humidity in the room. Going to the right at 60° F (16° C) air temperature we look for the Dew Point which is below the temperature of the meat (35° F, 2° C). It is found below the 35% relative humidity column and its temperature is 32° F (0° C). At 60° F (16° C) and 35 % relative humidity we will not have problems with moisture condensing on the meat.

Looking at the table we can see that when processing meats at 50° F (10° C) and humidity of 60 % or less, we should not have any problems with moisture control. Meats are normally processed at 50° - 53° F (10° - 12° C). Although processing meats at lower temperatures will be even better, lower temperatures will present too much of a hardship for people that would work many hours under such conditions.

Dew Point Table in ° C

 

Air Temp. in °C	% Relative Humidity
	100	95	90	85	80	75	70	65	60	55	50	45	40	35	30	25	20	15	10
18	18	17	17	16	15	14	13	12	10	9	7	6	4	2	0
16	16	14	14	13	12	11	10	9	7	6	5	3	2	0
13	13	12	11	10	9	8	7	6	4	3	2	1	0
12	12	11	10	9	8	7	6	5	4	3	2	0
11	11	10	9	8	7	7	6	5	3	2	0.5	0
10	10	9	8	7	7	6	4	3	2	1	0
7	7	6	6	4	4	3	2	1	0
4	4	4	3	2	1	0
2	2	1	0
0	0

Humidity Measurement

The devices that measure humidity are called hygrometers and there are many to choose from.

 

inexpensive hygrometer	digital hygrometer from NovaLynx Company	hygrometer and thermometer from Maximum Weather Instruments

Traditionally humidity was measured by the dry and the wet bulb method.

Dry and Wet Bulb Method

Humidity can be measured indirectly with dry and wet-bulb thermometers. The dry-bulb is a common mercury/liquid thermometer to measure the air temperature. The wet-bulb is a second mercury/liquid thermometer whose bulb is covered by a muslin bag which is kept moist. Both thermometer readings are taken and the difference between them allows us to calculate the humidity using tables.

 

The simplest hygrometer known as "a sling psychrometer" can be made from two thermometers attached (tape, string or wire) to a wooden board and the mercury or liquid filled ends sticking over the edge of the board about 1" (2.5 cm). This thermometer is called the dry-bulb thermometer. The second thermometer has a wet cloth (gauze, muslin bag) around the thermometer bulb, and secured  with the rubber band or other ways, This thermometer is called the wet-bulb thermometer. The fan is needed to blow the air on the thermometers until both temperatures will stabilize and the readings are taken. Water will evaporate from a little bag cooling the wet-bulb thermometer. The temperature readings are taken and substracted to get  the difference. The humidity table is consulted. Find the dry thermometer temperature in the row on the left, then find the difference between two temperatures in the column on the top. Follow the air temperature to the right and follow the difference in temperature column down. The point where the row and column intersect is the relative humidity. The examples follow below. A better model can be made by drilling a hole in the top of the board and attaching a handle with a rope or a short piece of chain so that the whole assembly can be whirled around (no fan needed now). During the whirling, the water evaporates from the wick, cooling the wet-bulb thermometer. For the most accurate reading, swing your psychrometer for several minutes, until the thermometer wrapped in cloth gives a constant temperature reading. If the ambient air is dry, more moisture is removed from the bag or wick, cooling the wet-bulb thermometer more and the temperature difference between two thermometers will be greater. The wet-bulb thermometer always gives lower readings than the dry-bulb because of the cooling effect of moisture evaporating from the muslin bag. If the air is very humid the difference will be smaller. If the relative humidity is 100 %, there is no difference between the two temperatures.

 

	A pocket sling psychrometer. Note the muslin bag on wet-bulb thermometer. Photo courtesy NovaLynx Corporation
	A sling psychrometer Photo courtesy NovaLynx Corporation

Relative Humidity Table

The following table is just a small section of the complete humidity tables:

Note: Numbers in blue color denote relative humidity.

Example 1: Dry bulb thermometer shows reading of 70° F and the wet bulb thermometer shows 60° F. Find the relative humidity. The difference between readings is: 70 - 60 = 10° F. Following 70° F dry bulb temperature to the right and 10° F difference between dry bulb and wet bulb temperature down we can see that they intersect at 55 % relative humidity.

Example 2: Dry bulb reads 76° F and the wet bulb reads 62° F. Find the relative humidity. The difference is 76 - 62 = 14° F. Following 76 °F dry bulb temperature to the right and 14° F difference column down we can see that they intersect at 44 % relative humidity.

Note: there are also tables in  ° C and they can be found on the Internet.

National Weather Service Relative Humidity and Dew Point Tables for Different Elevations using Dry-bulb and Wet-bulb temperatures

Without a doubt the most complete set of tables come from the National Weather Service. There are 7 sets of tables, each for a different elevation. Different readings will be obtained when taken at the sea level (altitude 0 feet) and different readings will be obtained in Denver, Colorado also known as the 1 mile city. Denver lies over 5,000 feet above the sea level. At first these tables may seem to be a little intimidating, but they are very accurate and the dry and the wet bulb temperatures, relative humidity, and the dew point, all are included in one table.

Below we present a part of the National Weather Service table that covers dry bulb temperatures from 61° - 65° F for the elevation 0 - 500'.

Wet Bulb Temperatures (40, 41, 42 etc)

First left column - Dry Bulb Temperatures (61, 61, 63, 64 and 65).

Example 1: Find the relative humidity if the wet bulb temperature is 54° F and the dry bulb temperature is 61° F?

Answer: Find the wet bulb temperature at the top of the table (54° F), then move down the column. Find the dry bulb temperature at the left side of the table(61° F), then move to the right. The intersection of the wet bulb column and the dry bulb row is a cell  with two numbers: 48 and 63. The lower number in blue (63) is the relative humidity and the upper number in red (48) is the dew point temperature.

Example 2: Find the dew point temperature when the wet bulb reads 65° F and the dry bulb reads 50° F?

Answer: The 65° F dry bulb temperature row and the 50° F wet bulb temperature column intersect at the block  of numbers 34 and 31. The red number 34 is the dew point temperature.

Example 3: Let's assume that you would like to double check the data from a different table with the National Weather Service table. All you have is the dry bulb temperature of 64° F and the difference between the dry and wet bulb of  10° F.

Answer: We have to find out the wet bulb temperature and we know that the wet bulb temperature is always lower. 

64 (dry bulb temp) - x (wet bulb temp) = 10

The wet bulb temperature is 54° F and at the intersection of the 64° F dry bulb temp and the 54° F wet bulb temperature column we find a block with 46% relative humidity and 51° F dew point temperature.

Notes:

• http://www.wrh.noaa.gov/sto/rhtbl.php - complete relative humidity and dew point tables for different elevations from the National Weather Service
• In air conditioned houses the relative humidity remains at the same comfortable level of about 40 - 45 %. The coils of the air handler act as a dehumidifier and remove the moisture of the air. This moisture is water that is dripping from a little drain pipe on the outside.
• In a home refrigerator the humidity remains at about 45% at 40° F (4° C) and about 70% at 0° F (-18° C) in a freezer.

Page added on November 12, 2006.

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