Donut Frying Fat Technical Help

Donut Frying Shortening is the major part of the processing environment which all donuts must perform in.  The fat acts as the heat transfer medium and it will also be a major component of the finished product. Fat in donuts strongly influences flavor. Many flavor components are fat soluble and are held in this phase and are slowly released during consumption. Fats also react with sugar and proteins during the frying process giving the pleasant fried flavors.

The frying fats used in the bakery can have different compositions which can cause profound differences in the performance of donuts.  Using the wrong fat can result in excessive fat absorption resulting in greasy donuts that are not palatable. Various compositions of frying fats are used in frying donuts for such reasons as price, availability, dietary laws and regional preferences.  In addition, fats can change chemically in the frying process. And this can increase the variations of frying fat compositions donuts must be subjected to.

Frying fats used for donuts has 1 major difference when compared to traditional food frying fats: Free fatty acid levels need to be higher. Fresh fat (low in free fatty acids) will result in low fat absorption and pale crust color.

There are many good frying fats,  but we must remember that no two bakeries are the same, and it pays to pre-test and select the correct frying fat for your operation and the field conditions.

Bakers will have many questions on frying fats,  and it is wise that they not only talk to the shortening manufacturers, but also, the mix manufacturers. 

Function of Donut Frying Shortening

Frying fat serves as a heat transfer medium, as well as being absorbed into the donut to improve the eating quality and shelf life.  Fat contributes to the flavor of the product and causes the sugar coating to adhere to the donut.

Frying fat is one of the more costly ingredients in a finished donut.  When frying fat breaks down with use, the product quality not only suffers, but the cost of the donuts goes up due to the increase in the amount of fat absorbed by the donuts.

Composition of Donut Frying Shortening

Fats are compounds of glycerine and fatty acids.  The various fats differ in the type of fatty acids in their composition:

Examples:
Saturated fatty acids, such as stearic and palmitic, when bound to glycerine, form the hard fats.  Unsaturated fatty acids such as oleic, linoleic and linolenic, when bound to glycerines form liquid fats or oils.

 

Trans Fatty Acids in Donut Shortening

We can assist you with converting to trans fat free oils. Be aware that there are limitations. Generally speaking going trans fat free means converting to Palm oil based shortenings. These are not significantly healthier.

Trans fats are formed when liquid oils go through a process called hydrogenation. Hydrogen is added to make the oils more saturated or solid. Hydrogenated oils are used by bakeries for many technical reasons, specifically, longer rancid free shelf life and proper texture. Trans fatty acids also occur naturally in beef, butter, milk and lamb fats and in commercially prepared, partially hydrogenated margarines and solid cooking fats. Partially hydrogenated vegetable oils were developed in part to help displace highly saturated animal and vegetable fats used in frying, baking and spreads.

Evidence suggests that consumption of trans fats raises LDL (bad) cholesterol and lowers LDL (good) cholesterol, increasing the risk of heart disease and stroke.

With states now banning trans fat from restaurant use, it is only a matter of time before trans fats are an ingredient of the past. Unfortunately trans fats are being replaced with palm oil.

The only choices for frying donuts at this point are:

1. Partially hydrogenated Vegetable oil ( contains trans fat)

2. Animal Fats (contain some trans fat)

3. Vegetable oils containing  High levels of Palm oil blended with other oils

As you can see, none of the choices are healthy. 

Donuts can not be fried in canola oil, soy oil or any other liquid oils. Many articles are talking about replacing trans fats with canola oil. This can not be done. Oils that are liquid at room temperature will leach out of the donut and will make an oily mess. Solid fats are needed for sugar white and glaze stability. Donuts fried in liquid oils are VERY greasy and unsalable.

Esterified oils are available, but they are expensive and can have flavor issues.

Fat Breakdown of Donut Shortenings

Palm oil based shortenings are not as stable as the old Trans containing partially hydrogenated shortenings. Palm oils start out with a high level of Total Polar Materials. Total Polar Materials is a measurement of all non triglycerides in the donut shortening. Total Polars is one of the best indicators of donut frying shortening quality. The old standard test of Free Fatty Acids is not as good an indicator of used donut frying shortening quality. p-Anisidne Value is a good indicator of flavor deterioration of donut frying fats.

Total Polar Materials

The fryer, the volume of oil, the temperature of the frying oil, and the condition of the food entering the fryer are all generally controlled and may, therefore, be considered constants in most fryer operations. Yet the quality of the food as it exits the fryer changes over time. The changing variable is the frying oil itself. What begins as a nearly homogeneous mixture of triglycerides (fresh palm oils are 92-95 % pure triglyceride) is altered through exposure to the food, high temperatures, and metals in the fryer, the air, and reactions between food and degradation products in the oil to become a mixture of literally hundreds of compounds. Individually, most of these compounds have little effect on the food being produced, but taken as groups, they can be shown to do so.

The best measurable index of oil quality, especially in regard to oil discard point, is the total polar materials (TPM). Polar materials may be simply defined as all non-triglyceride materials in an oil. For example, the fresh palm oil described earlier contained 92-95% triglycerides. The remaining 5-8 % are considered the polar fraction.

As an oil breaks down, the triglycerides break down and the total polar materials increase. In measuring TPM, you are measuring accumulated degradation products.

p-Anisidine Value

The oxidative process of fryer fats is one of the main causes of the deterioration of the principal flavor characteristics of donuts.

The complex oxidation process can be summarized into two phases:
The fatty acids react with oxygen and produces odorless compounds such as peroxides
The peroxides further degrade into many substances as volatile aldehydes which are responsible for the rancid odors and flavors.

The primary oxidation products are normally measured with Peroxide Value test (PV) and the secondary products with p-Anisidine tests.

The oxidative status of a fat should be evaluated considering both its primary and secondary oxidation. In fact a fat that has initially a high peroxide value, kept in storage for a long time in absence of oxygen, has a secondary oxidative process that decreases the peroxide value but increases the anisidine value.

The following are some of the general indicators of fat breakdown:
                    Darkening of the fat
                    Development of off flavors
                    Smoking of the fat
                    Foaming on the fat surface
                    Gum formation on exposed metal parts of the fryer


Some of the Chemical changes of the frying fat due to  breakdown:
          Density                       Increases
          Viscosity                     Increases
          Titratable Acidity        Increases
          Melt Point                    Decreases
          Flash Point                  Decreases
          Solid fat index SFI     Decreases
          Congeal Point              Decreases
          Iodine Value                 Decreases
          Crystallization Rate      Decreases
          Cloud Point                  Decreases

Free Fatty Acids
Donut fat breakdown at normal frying temperatures is caused by hydrolysis of the fat at the point where the fatty acid connects to the glycerol. The addition of a water molecule at this point will release a fatty acid. The result is a free fatty acid (FFA)and a diglyceride. The normal frying process releases steam which will cause this reaction to occur. In addition oxidation (from air or air jets blowing into the fat) can cause an increase in the FFA.

A small amount of FFA in the donut frying fat is desirable. Fats with a FFA of over 0.1% will just begin to smoke. FFA must be present in the donut shortening to obtain a quality product. FFA in the fryer should be between 0.3% and 0.75%. Ideal levels are .4 to .5%. Donut shortening that is too fresh or not broken in will have too low a FFA content. The FFA content increases as the donuts are fried and the addition of fresh shortening will lower the FFA. It is a balance between these two that maintains the FFA level.

Fresh fat with no break-in period may contain less than the optimum amount, the result being a ragged break, low fat absorption, and a pale crust on the doughnut. Excessive free fatty acids will produce excessive fat absorption, dark crust, misshapen sugared doughnuts. Excessive free fatty acids can be determined by darkness of color in the frying fat, excessive foaming, and excessive smoking above the fat

Free Fatty Acid Testing

2 oz ss ladle   

250 ml PTFE beaker

250 ml drop bottle polyethylene

15 ml self zero self supporting burette

Chemicals
0.1N Sodium Hydroxide 1 liter size 

Ethyl Alcohol 90% denatured  

Phenolphthalein 

hotplate stirrer

stir rod     

       
Prep
1.  Fill drop bottle with Phenolphthalein and label
2.   Fill burette bottle with .1N Sodium Hydroxide

Sampling
1.  Use SS ladle to remove fat from fryer and place in PTFE Beaker

Testing
1. Wear Eye protection
2.  Weigh 50 g of fat into clean PTFE beaker.  Record Weight
3. Add approximately 100ml of ethyl alcohol to fat. 
4.  Add 5 drops of phenolphthalein to fat/alcohol.
5. Put stir bar into beaker
6. Place beaker on hot plate and heat on med low  heat.  PTFE Beaker will melt above 500F.  Heat until alcohol boils.
7. Add sodium hydroxide to burette so that it reads zero (0)
8. Turn on stirrer
9. Slowly drip sodium hydroxide into boiling solution until the color changes and stays light pink.  Record ml of sodium hydroxide added.  Do not add to fast or you could go past endpoint

FFA=  ml of sodium hydroxide*.1*28.2
                         Grams of Fat

 

Types of Donut Frying Shortening

There are several sources of stock materials for frying fats.

Animal Fats
Beef Tallow and Lard

Vegetable
Soy Oil, Cottonseed Oil, Palm and Coconut Oils are the most common.  Corn, peanut, Safflower, sunflower and Canola are not as common due to flavor, cost and functionality issues.

Animal fats have been used for years in the baking business.  Animal fats have been phased out of most  bakeries for health and religious reasons.  However, they are making a comeback due to the lack of hydrogenation and thus trans fats. The majority of bakeries on the east and west coasts need to be Kosher certified for the large Jewish populations found there.  There are several other groups such as vegetarians and Muslims who look for the kosher label to indicated the absence of these fats as well.  Animal fats are still used on a limited basis in the central United States.  Animal fats will impart a distinct flavor and are usually more cost effective.  Animal fats can impart a very strong off flavor that gets stronger over time that can be of concern.

Vegetable Fats are the most popular with soy oil being by far the most predominate fat.  Soybean oil is partially hydrogenated to increase the melt point.  Very often a second fat such as cotton seed is added for flavor reasons.  The use of palm and coconut oils are becoming more common as more and more bakeries go trans fat free. Palm oil also has a distinct flavor and a highly deodorized palm oil should be considered.


 

Specifications of Donut Frying Shortenings

Most large producers of frying fats offer seasonal changes in frying fats (summer and winter blends).  The summer formula will be slightly harder and will have a higher SFC in the 30C range which will cause it to set faster in the hot conditions of a bakery. Seasonal blends are very important in areas with large differences in temperatures between summer and winter. Summer fats will have more solids/higher melting point fatty acids to reduce oiling out on hot summer days.


 Solid Fat Index vs. Solid Fat Content

Solid Fat Content (SFC) is the percent of shortening which is solid at various temperatures . The whole SFC curve is required in order to understand the properties of the shortening at different temperatures.

SFC is measured using pulsed nuclear magnetic resonance technology. An older method, using dilatometry, gives a Solid Fat Index (SFI) profile. Because of certain difficulties in the methodology the maximum SFI measurable is about 85 in a fully hydrogenated fat. The relationship between SFC and SFI is rather complex. Both methods are still in use, and either one may be found in specifications for commercial shortenings.

The plastic range refers to the range of temperatures over which shortening the plastic properties listed above. Assuming the shortening has the proper beta crystal structure, it will be plastic over a range of about 10 to 30 SFC units. The choice of upper and lower limits of plasticity depend upon the the application. For most purposes a broad plastic range is preferable to a narrow one.