Introduction. Materials and Methods. How to Estimate Injection Percentage

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1 How to Estimate Injection Percentage Introduction The Marel IN33-3 injector for pork bellies is a 5 needle, low-pressure conveyor type machine which utilizes a 3-gpm positive displacement pump and control valve giving it tremendous repeatability and consistency. As normal injection conditions change during a production day, the machine settings need to be adjusted. The settings that can be readily changed are needle pressure, machine rpm, needle pattern (conveyor belt stroke distance), and stripper pressure. Understanding how one may alter these parameters to quickly dial in the target percentage is extremely useful. Development of a multiple parameter formula or equation would create a tool to enable quick estimates or training for anyone needing this knowledge. Materials and Methods The data used to prove out this formula was acquired by injecting pork bellies at commercial production facilities with a prototype machine. Before and after weights determined the injection percentage. Belly characteristics in general varied widely and the bellies came from various suppliers. All product tested was made into American style bacon for retail, restaurant, and food service customers. Belly temperatures at injection ranged from 3-5F and belly characteristics of fat and lean were noted if exceptional. Needle pressure ranged from 33 to 51 psi, injector rpm settings tested were 75, 1, and 115 rpm, and needle patterns of 3.75 and 3.5 inches were used. Needle pattern is the same as the stroke distance of the conveyor. The definition of injection percentage is: IP=(wI-w/w)x1 where w=raw weight, wi=injected weight, and IP=injection percentage.

2 Results and Discussion The early version of the multiple parameter formula developed to estimate IP is as follows: IP= (needle pressure / needle pattern) This was developed out of the observation that a common needle pressure setting of 3 psi and a common conveyor stroke setting of 3.75 inches, when divided, resulted in a common injection percentage of about 1%. It becomes clear in this formula that as needle pressure increases, IP would increase, and as needle pattern decreases, as long as needle pressure is constant, IP would again increase. All based on this simple fraction. This is known information in bacon injection and since there was no available data gathered using multiple needle patterns, a standard 3.75 inch needle pattern was used in the formula. It is the highest throughput setting of the Marel IN 33 and used during the majority of testing. A few tests were conducted using a 3.5 inch needle pattern. Stripper pressure was excluded as a factor in the equation since its effects on IP are marginal. The formula was continually changed to include machine speed, since speed has an effect on IP. Through trial and error, it was discovered that (needle pressure / needle pattern) multiplied by (1 / actual machine speed) was accurate. The 1 comes from the machine s top speed and any other speed placed in the denominator under it, would create a fraction which grows approximately in proportion to an IP increase (due to needle dwell time) at lower speeds. Therefore, formula # for the IN 33 became: Estimated IP = (injection pressure/3.75) x (1/actual rpm) The results of version two were a little high, so a square root was applied to the dividend of (1 / actual machine speed). It lowers the answer slightly when estimating results below 1 rpm. At 1 rpm, the dividend of (pressure/3.75) works well alone and the speed multiplier becomes one, since (1/1) =1, which negates speed as a factor in this case. At speeds lower than 1, (pressure/3.75) is multiplied by factors increasing from one and form a multiple resulting in an estimated IP close to actual results. Note the similar lines of slope between the actual and predicted results in Fig.1. So the final version of the formula to predict injection percentage is: Estimated IP = (needle pressure/3.75) x (1/actual rpm)

3 Fig. 1 Equation v. Actual 5 Sample 3.75" Stroke, 3-5 psi EQ. 115 RPM EQ. 1 RPM EQ. 75 RPM Actual 75 RPM Actual 75 RPM Linear (EQ. 115 RPM) Linear ()

4 Injection Percentage % Figures, 3, and show formula predictions. These are for three different rpm s each with needle pressure ranging from 3-5psi. Needle patterns were held constant at 3.75 inches. These graphs show that injection percentage increases in a positive linear manner as needle pressure increases. Higher machine rpm shifts the injection percentages lower because at higher rpm s, the residence or dwell time of needles in the product decreases, allowing less time for brine to be injected and consequently less IP. This is why it was important to add a speed part to the formula. Fig RPM, 3.75 Stroke Results: approx. 1-1% IP (Pressure/3.75) * SQRT(1/actual rpm) Fig RPM, 3.75" Stroke Results: approx. 9-1% IP (Pressure/3.75)* SQRT(1/actual rpm)

5 Fig RPM, 3.75 Stroke Results: approx. -15% IP (Pressure/3.75) *SQRT (1/actual rpm) The faster the machine injects, the lower the injection percentage. The opposite is also true. When the residuals for the 59 samples available for this study were calculated and graphed, the resulting correlation coefficient was.51. To achieve a 99% confidence for a data set this large, a correlation coefficient of only.115 is required. Regression and residual symmetry were calculated using Excel. (see Figure 5) Fig.5. Residual Symmetry.... y =.3x Linear (Trend) Number of Samples: 59

6 From Figure below, it can be observed that there is an inverse relationship between injection percentage and needle pattern, with injection percentage declining as needle pattern distance increases. This is due to fewer piercings into an injected area as the needle pattern is increased. Fig. 1 RPM, psi pressure, with varying stroke settings (.9375"-3.75"; IP=.7-11.%) Stroke distance in inches (Press/Patt'n)*SQRT(1/actu al ) While the chart above is factual in its estimation of the effect of conveyor stroke on IP, there is no data presented here to quantify it. As stated previously, only stroke settings of 3.75 and 3.5 were tested. However, the formula has the ability to estimate IP at lower stroke settings as is shown, when replacing 3.75 inches with some lower figure. Summary The formula, Estimated IP = (injection pressure/3.75) x (1/actual rpm), is a means to estimate injection percentage results prior to running bellies or to inform interested customers or sales persons of the IN 33 s capability. It works well for this machine and was created by observation and trial and error. Variants of the formula could be developed for any injector or any meat product. The first part of the formula accounts for needle pressure and conveyor stroke distance and gives a result with these two settings. The nd part adds to and predicts changes when machine rpm is considered. These three factors are the primary settings to consider when injecting any product. Bill Scarpino Research & Development Technician Marel Bill.Scarpino@Marel.com