Coffee grounds tend to be rather high in nitrogen so in large quantities they will heat up the bin like in traditional composting. All the common bedding materials are high carbon sources in traditional composting. On this observation alone I would not consider the used grounds to be bedding.

I've seen mixed results on used-coffee-ground pH levels. Some say that the acidity leaches out into the coffee drink while some say they remain rather acidic. My step father, a PhD ag-chemist, collected grounds to mulch in around his acid loving plants.

As a side note UCG's are ready to use in the garden as they are. There is no need to compost them prior to mixing into the soil. They will break down in place and act as a time release fertilizer. I did this with great results until I noticed that my dog also ate the grounds. A caffeine-wired terrier is not what I want as a pet.

Food. Yep they have nitrogen (considered greens for composting) and they don't hold water at all. You can load them in soaking wet in big mounds, but a couple of days later in a fabric bin system they can be bone dry, a bit of a pain. Why I mix them with other stuff.

In that orange monster you could run two sections side by side. Regular worm stuff, your coffee/hay mix beside. Once it's 'aged' the worms can move over by themselves. If each is in it's own section (above a harvest hole) you can see if there's any different in the end product also.

This is taken from my files...I take no credit for this information and have no idea of its propriety.

STAR BUCKS COFFEE GROUNDS ABSTRACTS
Star Bucks coffee grounds provide generous amounts of phosphorus, potassium, magnesium, and copper. They also release nitrogen into the soil as they degrade. And they are slightly acidic.
Use of Starbucks coffee grounds in amending mineral soils up to 35 percent by volume coffee grounds will improve soil structure over the short-term and over the long-term. Use of the coffee grounds at the specified incorporation rates (rototilled into a 6- to 8-inch depth) will substantially improve availabilities of phosphorus, potassium, magnesium and copper and will probably negate the need for chemical sources of these plant essential elements.
The nitrogen, phosphorus, potassium "guaranteed analyses" would be as follows for the coffee grounds:
Nitrogen: 2.28 percent
Phosphorus: 0.06 percent
Potassium: 0.6 percent
Available nutrient levels: The pH or reaction of the coffee grounds is considered slightly acidic and in a favorable range at 6.2 on the pH scale.
Salinity (ECe) is a measurement of total soluble salts and is considered slightly elevated at 3.7 dS/m. The primary water-soluble salts in this product are potassium, magnesium, sodium and chloride. The potentially problematic ions in sodium and chloride are each sufficiently low as to be inconsequential in terms of creating problems for plants.
The availabilities of nitrogen, calcium, zinc, manganese and iron are quite low and in some cases deficient. Thus, the coffee grounds will not supply appreciable amounts of these essential plant elements when used as a mineral soil amendment.
However, the availabilities of phosphorus, potassium, magnesium and copper are each sufficiently high that there will be a very positive impact on improving availabilities of these elements where the coffee grounds are used as a mineral soil amendment. The coffee grounds will negate the need for additional sources of phosphorus, potassium, magnesium and copper when blended with mineral soils.
In summary, the available plant essential elements which will be substantially improved where the coffee grounds are used as a soil amendment, include phosphorus, potassium, magnesium and copper.
Total nutrient levels: Each cubic yard of these coffee grounds contains a total of 10.31 lbs. nitrogen, of which 0.01 lb. (0.09%) are available. Thus, even though available nitrogen is considered deficient in this product, there still remains over 10 lbs. of total nitrogen per cubic yard of coffee grounds. Thus, nitrogen is primarily bound in the organic fraction and is unavailable to plants until soil microorganisms degrade the organic fraction. Through this process, the nitrogen is converted to plant available forms. Over the long term the coffee grounds will act like a slow release fertilizer providing long-term nitrogen input which can then be utilized by plants.
Nearly all potassium and all magnesium are in the available forms. This means that immediate availability improvements for these two elements will take place when the coffee grounds are blended with mineral soils. About half of the copper and calcium are in their immediately available forms.
All other plant essential elements are primarily bound in the organic fraction and will thus be subject to slow release over time as soil microbes continue to degrade the organic fraction.
Physical properties: Virtually all particles passed the 1 millimeter (mm) screen resulting in a product which is very fine textured. Each cubic yard of the coffee grounds will supply an excellent amount of organic matter, measured at 442 lbs. organic matter per cubic yard. At the use rates indicated in this report, the input of organic matter will be substantial and will result in considerable short-term and long-term improvement of mineral soil structure.
Carbon/nitrogen ratio: On the basis of dry matter bulk density (452 lbs. per cubic yard), organic matter content (97.7%) and total nitrogen (2.28%), the estimated carbon/nitrogen ratio is about 24:1. This means that there is more than sufficient nitrogen present in the coffee grounds to provide for the nitrogen demand of the soil microorganisms as they degrade the organic fraction.
Use rate: Based on the overall chemistry and physical properties of the coffee grounds, they can be utilized at rates similar to other organic amendments when used in amending mineral soils. These data indicate that 25-35 percent by volume coffee grounds can be blended with mineral soils of any type to improve structure of those soils.

I'm finding my fabric flowthru systems are drying out fast and one experiment I have thought about trying is use coffee to water them. If you steep the water with the used grounds some nutrients should leach out then you're left with grounds to mix directly into garden beds.

I did this once and mixed the top few inches of my fabric FT and it did warm up a little by the next day. It was warmer than ambient but by no means hot.

Morgan3. Thanks for the coffee info. I'll have to copy this to my files.

Thanks, everybody!

If you can, compost your hay and UCG on the ground for a month or so. A few years back I made several compost piles using straw, large bags of starbucks UCG, and aged horse manure. In the spring these piles had more worms than my bins!

Mr Yan, I've never watered my inn with coffee, but I certainly have soaked my cardboard/eggcarton material in waste/french press coffee before adding when I've had it around (or if I've got a dryish mix, bread etc.). I don't worry about experimenting with stuff when worms have the choice to go in it or not and/or wait a while until it's ready, not so much when I'm dumping it on them or the worms in them directly. You could always do a mad scientist test on a few worms.

The dry sides on the inn are tough. The top sides you can keep moist with watering, the bottom sides seem to get processed due to compression of all that moist VC sitting on it. But there's that below the top, above the bottom sides where it does get try. I've ending up leaving it as trying to get it wet got me water coming out the bottom and that can drip for days lol. Water aways seems to deflect to the center. I've found it all gets processed in the end anyway.

In worm composting vernacular anything high in nitrogen is food. That includes coffee grounds.

As for nesting in them vs eating them, worms nest in both bedding and food, Worms eat both bedding and food. You will often see more worms in the food, because it breaks down faster, so it has more microbes in it than the bedding. Microbes are what the worms are really eating.

My experience is that coffee grounds decompose slowly at first. They will grow fungus on them, at which time they decompose faster. Worms tend to leave them alone until after the fungus appears.