My perspective (as an agronomist and former licensed grain grader) may shed some light on bitter millet, which also makes other grains and milk have an off-flavor or bitter. Harvesting proso or any grain prematurely does not allow chlorophyll to finalize conversion to mature sugars and starch. It would be like the bitterness of eating green bananas compared to yellow ripe ones. 1.) *Odor *can be from many causes. Cows milk tastes different in spring after cows transition from winter (dry) forage to grazing spring grass. As a kid milking cows and drinking milk, no doubt milk taste changed. I used to think it was cows eating wild onions in our spring pasture. Later I realized it was the cows' rumen bacterial profile had to change and digest a different forage. Within a couple weeks, the milk went back to what I will call "good winter flavor." Therefore, as it relates to millet tastes, bacterial contamination from harvest, transportation and storage often caused by "wet spots" (especially in storage) that produces billions of bacteria/fungi which when the bin is emptied spreads the contaminant throughout the grain handling system--thereby contaminating all grain. Also, grain, including millet, transported or stored near fertilizer, pesticides, fuel, or other smelly products may not contaminate the grain, but can give it an odor. (That is why cereal is not stocked with soaps or dryer sheets in grocery stores.) *Suggestion*: To prevent, or minimize, millet's bitterness, the incoming grain sample should be smelled (off odor), inspected and rejected for moldy kernels, insects and rodents, and consider using electronic light detection (ULV), infrared (NIR), and ultraviolet (for rodent contamination) methods. See: a.) The use of polarized light and image analysis in evaluations of the severity of fungal infection in barley grain - ScienceDirect <https://www.sciencedirect.com/science/article/abs/pii/S0168169918304812>; b.) Study: Innovative light technology is safe, effective for mitigating fungal contamination of cereal grains | Food Science & Human Nutrition | Illinois <https://fshn.illinois.edu/news/study-innovative-light-technology-safe-effective-mitigating-fungal-contamination-cereal-grains> ; c.) Techniques for insect detection in stored food grains: An overview - ScienceDirect <https://www.sciencedirect.com/science/article/abs/pii/S0956713518303372>; d.) Book1.pdf <https://www.ams.usda.gov/sites/default/files/media/Book1.pdf> (which is USDA's FGIS handbook) specifically see pgs. 1.19-22; e.) (PDF) Rodent pest of stored grain and their management <https://www.researchgate.net/publication/361184266_Rodent_pest_of_stored_grain_and_their_management> ; f.) B-260 UV Lamp Detects Rodent Contamination - Pest Control Technology <https://www.pctonline.com/news/b-260-uv-lamp-detects-rodent-contamination/> . 2.) *Premature harvesting* millet can have excessive green kernels (seeds) placed in storage. Proso, especially, is known for developing secondary and tertiary seed heads--after rains up to two weeks before physiological maturity. In windrows those seeds will dry with the hulls turning very white even if not pollinated. If millet is harvested under 15% moisture, those immature seeds may not be detectable in the combine grain tank because they are likely, and should be, blown out with the straw and chaff. Growers get anxious to harvest and generally harvest proso several days too early (to minimize shattering, or avoid expected bad weather). *Suggestions*: a.) Do not prematurely swath millet. Three years ago I published a special YouTube video on when to harvest proso. As of this morning, it had 11,411 views. See https://youtu.be/6kxx9Wt2jdo?si=2Hgi-A4b2d6mfCb2. b.) Increase air on combine. That will blow off light, immature seeds and increase test weight. c.) Food and beverage processors should buy heavier (# 1 Grade =>56/lb./bu.) test weight millet. 3.) *Weed seeds* can cause off-odors in millet and other grains. That is why I have "Certain Quality Determinants" in proso grading standards. All incoming millet should be inspected for cockleburs, pennycress, crotalaria, and castor beans. Crotalaria and castor beans are toxic but not normally found in proso millet fields. Cockleburs have very large seed and should have been separated on the top combine sieve and carried out with straw. Pennycress is especially garlic-smelling in spring and should be killed by spray or tillage before planting proso. It is a winter-annual, so could possibly germinating and greening before proso harvest. I've never seen pennycress seeds in proso millet grain because their thin-flat "penny" (shape and color) should have been separated by combine sieves, and blown out with straw and chaff. *Suggestions*: a.) Before unloading incoming proso, smell load and reject if it has an odd smell. b.) Inspect and reject load containing cockleburs, crotalaria, castor beans, and pennycress seed. c.) Ask farmers if they saw or smelled any pennycress when swathing or combining proso. Even driving down roads with fields contaminated with pennycress the odor can be smelled even if vehicle windows are rolled up. Fall germinating pennycress (a winter annual) will have very small roundish leaves and should be too short to get cut with swather. However, proso swaths laying on pennycress infested fields can pick up pennycress's garlic odor. All food processors should inspect and smell all loads of proso and other grains before unloading. That is why we must adopt Proso Grain Standards to separate low quality (#2, #3 and Sample) grades from # 1 proso millet....Gary Wietgrefe On Tue, Feb 4, 2025 at 9:50 AM Don Osborn <don@milletsalliance.org> wrote:
Millets sometimes have a bitter aftertaste. What are the causes and how to deal with them?
We had a short discussion offline, and Gary Wietgrefe's thoughts with regard to proso in particular wee detailed and specific. I'll copy them in a reply to this email, for your information.
First, if I may, I personally haven't noticed problems with the millets I consume, apart from one batch of little millet (our millet-of-the-month in February, by the way) which became musty - I think the batch was a bit old to begin with.
In any event, bitterness is an issue that consumers do bring up, and it stands in the way of wider use and acceptance of any grain or food (apart from those always bitter by nature, like bitter melon).
In millets, bitterness may be related to issues like premature harvest or poor grain quality. In some cases, I understand that the variety or cultivar of a millet may be naturally more bitter than other varieties of the same grain.
Don
DO, EL, MI, US NAMA