Warehoused cheese can help to lessen the summer electricity crunch in Wisconsin, a study at the UW-Madison”s College of Agricultural and Life Sciences has shown.
Each year, Wisconsin cheesemakers produce nearly a billion pounds of Cheddar and other cheeses that must be aged before they’re eaten. Aging occurs in refrigerated warehouses that hold millions of pounds of cheese. Using this stored cheese for “thermal storage” could cut the industry’s electrical bills and reduce peak electrical demand, according to Doug Reinemann, a milking systems researcher at CALS.
Thermal storage evens out electrical demand by using more electricity at night, when there is less demand, and using little or no electricity during the day. This can be crucial during hot weather when daytime demand strains generation and transmission capacity. Many utilities offer lower off-peak rates to industrial users, so banking cooling energy at night can save money.
The technique involves “depositing” cooling energy in stored cheese at night, by running the refrigeration system on high when demand and rates are lowest. The cooling energy is “withdrawn” during the day, by turning down the system when demand and rates are highest. A refrigerated warehouse may contain several million pounds of cheese that is aged for 60 days or more, thus providing plenty of thermal mass for this storage scheme.
Reinemann and his colleagues developed a computer model to simulate the effects of thermal storage, and they also built an experimental chamber to age real cheese under thermal-storage conditions.
In the computer simulation, the researchers created a worst-case scenario: a hot summer day (92 degrees F outside the warehouse); cheese entering the warehouse at 97 degrees F; a day”s production moved into the warehouse instantaneously rather than incrementally; and new cheese moved in at the beginning of the 12-hour “day” cycle.
Conventional cheese warehouses maintain constant temperatures of 40 degrees to 45 degrees F. In the computer simulation, the cooling system maintained air temperatures of 30 degrees F for 12 “night” hours. The system was shut off during the 12 “day” hours. The simulation showed that warehouse temperatures would reach 48 degrees F by the end of the “day” period.
Based on this simulation, the cheese in the experimental chamber was held at 30 degrees F for 12 hours and then at 48 degrees F for 12 hours over a 90-day aging period. This represented the most extreme temperature variations that cheese might experience during thermal storage, Reinemann explains. During that time, cheese temperatures varied by 6 degrees F in the center of the cheese block, and by 15 degrees F near the surface of the block.
A previous study showed that thermal storage offered considerable demand and cost savings. However, that study didn”t look at how temperature variations during aging might affect cheese quality. As cheese ages, milkfat, milk proteins and the bacteria in cheese cultures interact to produce the rich flavors and textures of good cheese. Swings in temperature can upset these interactions.
Three researchers from UW-Madison”s Center for Dairy Research sampled the cheese from the experimental chamber, and compared it with cheese aged at a constant 45 degrees F. The taste-testers had all served as judges in national and international cheese competitions.
Their verdict: the temperature cycling did no harm. They decided that the cycled cheese hadn”t aged quite as much as the constant-temperature cheese, probably because the average aging temperature was slightly lower for the cycled cheese.
Two cheese-industry groups also conducted informal tests. They sampled cheese from the face of the block, where temperature varied the most, and from the core of the block, where temperature varied least. They found no differences in flavor or texture between the two.
“Will cycling cheese warehouses save Wisconsin? Maybe not, but every little bit helps,” Reinemann says. “The technique could also be used for other refrigerated commodities.”
By the way, don”t try this at home unless you”re storing nothing but cheese in 40-pound blocks. The 48-degree peak temperature is too high to ensure the safety of other refrigerated foods, and most residences don”t get price breaks for shifting to off-peak electricity use.
This research was supported by a grant from the Energy Center of Wisconsin, which finds ways to use energy more efficiently by providing research, education and energy information.