Production of Bacteria-Free Walnut Kernels
ROGER W. PEASE, Assistant Hillculturist, West Virginia University,
Morgantown, West Virginia
Mr. Pease: Before I go into any detail about the construction of the pasteurizer, I am going to review the bacillus that causes the trouble very briefly. Most of you will know more about it than I do, but some of you may know less.
When the farmer takes the hulls from the black walnuts he generally spreads his hulled crop to dry almost anywhere. Rats will go over them, and these rats or mice infect the hulled walnuts with an organism called Bacillus coli that is on the outside of the shell. They go from there to the cracking plant, go through the cracker which thoroughly mixes up the infected nuts with the clean ones. They go from there to the separator, which does a better job at spreading the bacteria. Then they go on the market. If they are shipped from one state to another they are subject to inspection by Federal authorities. If they find this organism in the kernels, they may at their discretion heave the whole shipment into the river. They don't always do it. They haven't worked out yet a definite scheme to follow. In other words, they will not tell us, "If your kernels have a certain number of these B. coli in them we will let them by." As it reads, there should be not one organism there, and I can assure you that's almost impossible to get if a rat has crawled over those things.
Now, to get rid of poison ivy the best way is not to get it, and it's just the same with this organism. The place to get rid of it would be for the farmer to store the nuts to dry where the rats and mice cannot get to them and for the cracking plants to do the same. Unfortunately, this isn't done and sometimes isn't practicable. The next place to hit them would be before they are tumbled, that is, before the black powder on the outside of the shells is shaken off in a tumbler, or immediately after that to disinfect the shell without hurting the kernel.
That is where we should have started at West Virginia, but we didn't. We began at the other end after the thing was through and began studying pasteurization. The Government had recommended, I believe, temperatures of up to 300°F. for pasteurization. We found out right away—that is, I didn't, Dr. Colmer and Harvey Erickson, who are now—one of them—in Baton Rouge and the other one in Seattle, and they would know about it. They found out that after temperatures of over 300° the nuts tasted toasted and they would not keep nearly so well or so long as an unpasteurized nut.
After inspecting what pasteurizers they could get access to they concluded some work was necessary, so they spent 12 months and found that at a temperature of 160 and humidity of 80 per cent a more efficient job of pasteurization was done, and at the same time the kernel was not hurt at all. The taste was identical with an unpasteurized nut, and it would keep just as long. At that point one of them, as I say, went to Louisiana and the other went to Washington, and the research fell on my shoulders, that didn't know much about it.
We started to construct the machine. Meanwhile, Mr. Erickson told me he had developed a new strain of bacteria which was much more hardy and 160 degrees at 80% humidity would not kill the thing. So we constructed our machine to run a temperature of 180 at 70% humidity for 30 minutes, and that will kill them.
Now, in 15 minutes I can't give you anywhere near all the details of construction of that machine. I can give you a few of the principles. On the outside, of course, is a well insulated box. The nuts are fed through the top with a revolving drum with fins on it. They comes down to a belt that travels this way for six feet, drops to another, travels back, a series of five belts. It takes them just half an hour to go through. The layer of nuts is perhaps three-eighths of an inch thick. The temperature is kept up with electric coils. It is regulated with a thermostat.
We had some difficulty with the humidity. Try it and see. As we raised our temperature it was hard to keep our humidity up. Finally we went back to the simplest thing, which usually works. We just took a pan of water, with a solenoid valve and float such as you have in the modern hot air furnaces and put a magnetic switch on it. As the water boiled it helped raise the temperature, and it gave off vapors. The automatic switch and the wet and dry bulb from the thermometer and thermostat will shut the water off and shut the heat off automatically when you get the required temperature and the required humidity. In that machine our nuts start at the top, take 30 minutes to travel through. From the time they start at the top until the time they get to the bottom they have a standard temperature of 180° plus the 70% humidity.