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From farm to table

Storage

While in transit from farm to table, food products require storage along the way. For canned goods, this storage typically consists of space available in the distribution warehouse, on store shelves or in a kitchen cabinet. However, for refrigerated and frozen products, storage in appropriate temperature-controlled units, such as refrigerators and freezers, is required. The energy associated with such storage is not insignificant.

Storage of refrigerated and frozen goods occurs in three relatively distinct units:

1 – Walk-in Refrigerators and Freezers used in distribution facilities and back of retail outlets 2 – Temperature controlled display (reach-in) cases at point of purchase
3 – Self-contained combination refrigerators/freezers within the home.

Walk-in coolers and freezers are room-sized insulated compartments which are refrigerated. As the name implies, walk-ins have an access door large enough for entry of people. They are used primarily for refrigerated storage of food and other perishable non-food items, such as flowers. In addition to use in the distribution chain, walk-ins are also used at retail centers for temporary storage of food prior to transfer to display cases. In supermarkets, walk-ins are generally served by larger central refrigeration systems which also serve display case circuits. In the distribution chain, the walk-ins generally have dedicated refrigeration systems.

As shown below in Table 5-1, energy consumption for refrigerated walk-ins is estimated at 0.41 mj/day/cf , assuming a 50% effective capacity for food storage. For a walk-in freezer, energy consumption is estimated to be 0.51 mj/day/cf.

Table 5-1 Energy consumption for different refrigerated and frozen goods storage

Storage MechanismTheoretical Storage Volume Energy Consumption 
 cfkwH/yrMJ/yrMJ/dayMJ/day/cf (50% effective storage)

Distribution Storage1

         
Walk In Freeze 607 15555 55998 153 0.505
Merchandising Walk In Cooler 2040 42306 152301.6 417 0.409

Retail Storage and Display1

         
Med Temp System          
Med Temp Racks   485700 1748520 4790  
Med Temp Display - 380 LF 3167 129600 466560 1278  
Med Temp Walk-Ins   83800 301680 826  
Condensers   49650 178740 489  
Med Temp Total 3167 748750 2695500 7384 4.66
Low Temp System          
Low Temp Racks   373300 1343880 3681  
Low Temp Reach In - 268 LF 3752 348200 1253520 3434  
Low Temp Single Level Open - 128 LF 640        
Low Temp Walk-Ins   50000 180000 493  
Condensers   49650 178740 489  
Low Temp Total 4392 2956140 2695500 8099 3.68

Residential Storage2

         
Side by Side 4.91*AV + 507.5 22 615.52 2215.872 6.070882 0.551898
Sid by Side with ice pass through 10.10*AV + 406 22 628.2 2261.52 6.195945 0.563268

1 Source-Westphalen et al
2 Source – Energy Star, 2004, Residential. AV = Adjusted Volume (1.63 x volume)


Retail refrigeration is typically divided into two distinct segments which have different technology and which are governed by different issues. The most visible, and energy intensive, part of these systems are the display cases which hold food for the self-service style of supermarkets. Hence they are primarily evaluated considering two criteria: food preservation and sales enhancement. The most common case types are:

  • Glass-Door Reach-Ins (commonly used for milk, butter, boxed frozen goods)
  • Open Multi-Deck (commonly used for fresh fruit and vegetable display, meats, cheese)
  • Open-Tub Freezers (commonly used for bagged frozen products and frozen meats & poultry)
  • Seafood/Deli Display Case.


A typically supermarket will have from 60 to 80 or more display cases. About half with be low and very low temperature cases (-15F to -35F) and the remainder medium temperature cases (10F to 35F)
As shown in Table 5-1, the energy consumption associated with the low and medium temperature retail displays is considerable, averaging 3.68 MJ/day/cf for low temperature systems and 4.66 mj/day/cf for medium temperature systems. The higher energy load for the medium temperature systems can be attributed to the higher percentage of open display footage in lieu of closed door display. For open displays, the air flow is blown over the open section of the case, creating an air curtain which separated food from the warmer store air. This is inherently a more energy intensive system than continuous cooling within a closed container.
While in previous times, stand-alone refrigerators and freezers for home storage were common, in today’s households they are typically combined into a single unit. In order for a home refrigerator (side-by-side unit) to carry an Energy Star certification, it must consume less than 4.91xAV+507 kw-hrs/yr., or 10.10xAV+406 kw-hrs/yr. for a side-by-side unit with an ice pass through. Assuming a 22 cu.ft. volume refrigerator and a 50% effective storage rate, this translates to 0.55 mj/day/cu.ft. for the side-by-side, and 0.56 mj/day/cu.ft. for the side-by-side with the ice pass through.
For purposes of the home refrigeration/freezing energy load, we have utilized the 0.55 mj/day/ cu.ft. consumption rate.
In addition the energy requirements to run the refrigerator/freezer, one must consider the duration of time that products are stored. Personal behavior and literature references inform us that refrigerated product typically is stored for five days within the distribution system, two days at retail display and three days at home, whereas frozen products can be assumed to be stored 30 days in the distribution chain, 15 days at retail and 45 days at home, for a total of 90-day shelf life.
The storage space requirement for these different types of packaging is shown below in Table 4-2 in the previous section. Combining these storage factors with the energy and time requirements indicates that the energy consumed for the storage of refrigerated goods ranges from 142 to 158 kcal/lb, with approximately 25% of this associated with home storage, the remainder for distribution chain storage (see Table 5-2 below). In the case of frozen goods, the energy requirements are significantly higher due to both the longer storage time and the higher energy Scientific Certification Systems – March 16, 2005 18 demands for keeping product frozen. The calculated energy consumed for the storage of frozen goods ranges from 940 kcal/lb to 1253 kcal/lb with approximately 80% of the energy associated with the distribution chain and 20% with home storage energy requirements.

Table 5-2: Energy consumption during distribution, retail and home storage

 Bulk RefrigeratedPortion RefrigeratedAverage
 MJ/kgKcal/lb% TotalMJ/kgKcal/lb% TotalKcal/lb% Total
Distribution 0.36 38.99 3.39% 0.31 34.12 2.02% 36.55 2.70%
Retail 1.64 177.70 15.43% 1.44 155.48 9.19% % 166.59 12.31
Home Storage 0.29 31.52 2.74% 0.29 31.52 1.86% 31.52 2.30%
TOTAL - Refrigerated Goods 1.93 209.21 18.17% 1.73 187.00 11.05% 198.11 14.61%
 Bagged Frozen GoodsBoxed Frozen GoodsAverage
 MJ/kgKcal/lb% TotalMJ/kgKcal/lb% TotalKcal/lb% Total
Distribution 1.34 144.71 6.01% 1.00 108.53 4.82% 126.62 5.42%
Retail 4.87 527.66 21.93% 3.65 395.74 17.59% 461.70 19.76%
Home Storage 2.18 236.37 9.82% 1.64 177.28 7.88% 206.83 8.85%
TOTAL - Frozen Goods 7.05 764.03 31.76% 5.29 573.02 25.47% 668.53 28.61%

Examining the total energy inputs in the ‘farm to table’ food chain, the range of percentages of energy consumed in storage activities (including both distribution chain as well as home) as a percent of the total energy consumption across the food chain ranges from negligible or zero for canned goods to over 40% for frozen items.

meal preparation

While there are many different ways to prepare products in the home, for purposes of this assessment we are evaluating the use of a microwave oven, as it is a common tool for heating or cooking fresh, frozen and canned product. On average microwaves consume approximately 1500 kilowatts when running.

According to manufacturers’ directions, the estimated time required to microwave 14 ounces of frozen beans is 5 1/2 to 7 1/2 minutes; for 8 ounces canned beans 2 1/2 to 3 1/2 minutes; and for fresh green beans, 5 to 7 minutes for 14 ounces. For canned soup, the recommendation is 2 to 3 minutes. Using the average time, we find that that the energy consumed for preparation of these products ranges from 0.7 mj/kg (canned soup) to 1.47 mj/kg (frozen green beans) (see Table 6-1 below).

Table 6-1: Energy consumption to heat select products using a microwave

 Power InputTimeEnergy consumedWeight of product heatedEnergy Consumed per product weight
 WattsMinkwhmjkgmj/kgkcal/lb
Frozen Green Beans 1500 6.5 0.16 0.59 0.40 1.47 159.34
Fresh Green Beans 1500 6 0.15 0.54 0.40 1.36 147.08
Canned Green Beans 1500 3 0.08 0.27 0.23 1.19 128.70
Canned Soup 1500 2.5 0.06 0.23 0.40 0.57 61.28

Examining the total energy inputs in the farm to table food chain as shown below in Table 6-2, the range of percentages of energy consumed in meal preparation (as applied to products that are heated) as a percent of the total energy consumption across the food chain ranges from 5% to 13% of the total energy consumed.

Table 6-2: Preparation Energy Inputs

MethodPackagePackaging Energy Inputs% of Total Energy Inputs
  MJ/kgKcal/lb%
Refigerated Bulk 1.35 146.25 12.70%
Portion 1.35 146.25 8.64%
Average 146.25 10.67%
Frozen Bagged 1.47 159.25 6.62%
Boxed 1.47 159.25 7.08%
Average 159.25 6.85%
Canned Ready Meal 0.57 61.42 5.41%
Fruit & Vegetable 1.18 127.83 7.96%
Average 94.63 6.68%

It should also be noted that there are many situations where products may be used directly from the package without heating. For example using canned green beans directly in a three-bean salad, using canned chicken in chicken salad, or using frozen blueberries in making a smoothie. In these situations, the energy consumed for food preparation is assumed to be negligible (i.e. zero). Therefore when performing a comparative evaluation across product options (e.g. fresh, frozen of canned green beans), energy used for meal preparation should be noted accordingly. For example, in preparing a three green salad, fresh and frozen beans would require cooking before use, whereas the canned beans can be used directly without additional heating.

Conclusions

As shown below in Table 7-1, the energy consumed in delivery products from farm to table is both significant in quantity as well as significantly variable across package options,

 Bulk RefrigeratedPortion RefrigeratedAverage
 MJ/kgKcal/lb% TotalMJ/kgKcal/lb% TotalKcal/lb% Total
Production 2.96 320.00 27.79% 2.96 320.00 18.91% 320.00 23.35%
Processing 0.08 8.83 0.77% 0.08 8.83 0.52% 8.83 0.64%
Packaging 1.50 160.64 13.95% 6.24 669.43 39.57% 415.04 26.76%
Transport 2.86 306.39 26.61% 3.36 360.32 21.30% 333.36 23.96%
Storage 1.93 209.21 18.17% 1.73 187.00 11.05% 198.11 14.61%
Meal Preparation 1.35 146.25 12.70% 1.35 146.25 8.64% 146.25 10.67%
TOTAL - Refrigerated Goods 10.68 1151.32 100.00% 15.72 1691.83 100.00% 1421.57 100.00%
 Bagged Frozen GoodsBoxed Frozen GoodsAverage
 MJ/kgKcal/lb% TotalMJ/kgKcal/lb% TotalKcal/lb% Total
Production 2.96 320.00 13.30% 2.96 320.00 14.22% 320.00 13.76%
Processing 7.62 825.00 34.29% 7.62 825.00 36.66% 825.00 35.48%
Packaging 1.67 179.70 7.47% 2.20 236.34 10.50% 208.02 8.99%
Transport 1.47 157.99 6.57% 1.27 136.51 6.07% 147.25 6.32%
Storage 7.05 764.03 31.76% 5.29 573.02 25.47% 668.53 28.61%
Meal Preparation 1.47 159.25 6.62% 1.47 159.25 7.08% 159.25 6.85%
TOTAL - Frozen Goods 22.25 2405.96 100.00% 20.81 2250.12 100.00% 2328.04 100.00%
 Canned Ready MealsCanned Fruits & VegetablesAverage
 MJ/kgKcal/lb% TotalMJ/kgKcal/lb% TotalKcal/lb% Total
Production 2.96 320.00 28.17% 2.96 320.00 19.92% 320.00 24.04%
Processing 2.41 261.36 23.00% 2.41 261.36 16.27% 261.36 19.64%
Packaging 3.48 373.85 32.91% 6.14 658.56 40.99% 516.20 36.95%
Transport 1.11 119.49 10.52% 2.23 238.98 14.87% 179.24 12.70%
Storage 00.0 00.0 0.00% 00.0 00.0 0.00% 00.0 0.00%
Meal Preparation 0.57 61.42 5.41% 1.18 127.83 7.96% 94.63 6.68%
TOTAL - Canned Goods 10.54 1136.13 100.00% 14.92 1606.74 100.00% 1371.43 100.00%

Based on this data, it appears the most energy effective method for product delivery is canned ready meals (1136 kcal/lb) followed by bulk refrigerated (1152 kcal/lb), canned fruits & vegetables (1607 kcal/lb), refrigerated portion (1692 kcal/lb), frozen boxed products (2250 kcal/lb) and frozen bagged products (2406 kcal/lb). In essence, bulk refrigerated items and canned goods such as soups move to market with the same level of energy consumption (1150 kcal/lb).. Canned fruits and vegetables, along with portion refrigerated product consume an additional 30% energy, increasing consumption to 1650 kcal. The most energy intensive methods, frozen bagged and boxed product require 100% more energy to bring the food from farm to table than the less energy intensive bulk and canned meals.

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