This year's harvest has many folks harvesting in colder than normal conditions. Frosty mornings and the threat of snow in the coming week's forecast across much of the midwest raises questions about frozen chaffers and sieves.
The problem arises when frosty or snow-covered corn is harvested. Frost or snow crystals melt or turn to sticky slush in the threshing cylinder. That moisture condenses or freezes when it passes over the chaffer and sieve, coating the louvers with either a frozen slush or a cement-like gray paste. Eventually the louvers are so clogged that the combine spews a golden trail of grain out the back no matter how wide open the operator runs the sieves.
Frozen sieves must be thawed, either by ambient temperatures warming above 40 degrees, or by moving the combine inside a heated building. I've heard of guys using tarps and kerosene-powered torpedo heaters to direct warm air into the back of combines, but I hesitate to encourage that procedure for fear of setting a combine on fire. I've also heard of guys using steam cleaners to clear clogged sieves--but that's a miserably messy job. Depending on the brand and style of combine, it's sometimes not terribly hard to remove the sieves and chaffers so they can be manually cleaned.
The best practice is to be cautious any time corn is frosty or snow covered. Don't harvest until frost or snow is totally gone or melted. Be wary of corn that has been snowed on---the snow may be melted off the outside of the husks and stalks, but it doesn't take a lot of still-frozen snow between the shucks or nestled in the tips of the ears or the stalk/leaf junctions to create big problems in the sieves.