I’ve read the two major books (Joann Grohman’s and Dirk Van Loon’s) on keeping milking cows, and I’ve read just about every article and subsection on the topic I’ve ever come across. To date I’ve found no one that has given an plan for an efficient, inexpensive, and easily available refrigerator for storing raw milk (or really any milk).
Small upright refrigerators are 1) expensive and 2) inefficient. They are generally at least $300 new and are usually much larger than is needed for one cow (especially when the calf is left with her). Any upright refrigerator allows much of the cold air inside them to simply fall out on the floor every time you open them, and their gaskets are not kept tight by gravity. Their principal advantage is that that they are easy to get stuff into and out of, their factory equipped thermostat is in the proper temperature range (33-40 degrees F), and they generally have a small fan in them that circulates the air to prevent thermal stratification (since hot air rises any insulated box will have warmer air at top and colder air at the bottom unless it is circulated).
To me, the considerable negatives to an upright refrigerator outweigh the small benefits when compared to a “hacked” chest freezer.
We bought a 5 cubic ft. chest freezer at Sam’s Club for an incredible $55 because it was a floor model (with dents and no cardboard box), but ordinarily costs $130 (less than half an upright of the same size). Chest freezers, because they are expected to operate below freezing temperatures, often have much better insulation and have their doors on top, which is a great advantage, since gravity helps keep it shut. They also don’t allow all the cold air to fall out the way a side door does. They do have some disadvantages, however. First their thermostat often cannot be adjusted to a range above freezing, and even if it could, it would probably would not be accurate enough. Also, they lack any type of fan to circulate cold air, so they have relatively severe thermal stratification. Without thermal ballast our freezer would freeze the bottoms of half-gallon milk jars and the safety thermometer at the top would be consistently above 40 degrees—the danger zone.
The solution to the thermostat is an easy one. Get a temperature controller. I recommend an Inkbird. These handy gadgets have a thermocouple that you can place inside the chest freezer and a power outlet that you plug the chest freezer into. It basically overrides the thermostat on the chest freezer and allows for very precise and accurate temperature control in the desired range (33-38 degrees or so).
The solution to thermal stratification remained elusive for a few weeks. I blundered around first by trying every conceivable position of the thermocouple inside the chest freezer and every conceivable programming for the Inkbird. I was thinking of installing one of those low-wattage cooling fans for a computer inside to circulate the air, but then an idea sort of mutually dawned on my wife and I. The problem with filling the chest freezer with water (as was historically done in springhouses and other places milk was kept) is that it can both freeze and will almost certainly someday leak and leave you with a mess. Then I thought that maybe I needed to put something in there that doesn’t freeze but has a reasonably high heat capacity and is clean: washed pea gravel.
I thought at first that it was pretty silly filling up a 5 cubic foot chest freezer with 2 cubic feet of washed pea gravel (which cost an outrageous $10 because I bought it in bags from Home Depot instead of a gravel company), but we found that it actually holds nearly as much milk as it did before, and doesn’t need to be shuffled around, and that you just pop the lid and grab the milk and you are out. In this tiny chest freezer we can easily fit 15 half-gallon wide mouth jars—that’s 7.5 gallons of milk—for our cow 3-4 day’s production (the calf gets the rest). Thermal stratification is now working to our benefit. Frost is forming about 2 inches above the gravel, which means the gravel is just below freezing. And all that thermal mass (about 100 pounds of it) helps even out fluctuations when new warm milk is added. The bottoms of the milk jars no longer freeze and even at the very top of the milk fridge it doesn’t get above 40 and usually hovers around 38 degrees.
So our milk fridge works out to be quite a deal:
-$55 for 5 cubic ft chest freezer
-$30 for the Inkbird
-$10 for the pea gravel (washed by hand with a pasta colander and a hose and then dried in the sun on boards).
-A bit of duct tape, a metal screw, and a wire holder (~50 cents)
That comes in at under $100 and should use well less than $15 per year of electricity since the Energy Star label has both a higher kWh rate that what we pay and assumes operation at below freezing temperatures. Such systems use so little electricity I’ve read of off gird folks powering these with solar panels and windmills!