Why does my horchata have too much sediment?

One technique which seems to be effective at straining out fine sediment is gel clarification with gelatin or agar. Dave Arnold's research on agar clarification culminated in an approach which uses agar, an ice bath, a whisk, a cheesecloth or muslin, and about an hour.

• Measure out 0.2% agar by weight (as a fraction of your total liquid quantity).
• Whisk it into 1/3 of the liquid to disperse, then bring to a simmer while stirring and hold it there until the agar is hydrated.
• Pour in the rest of the liquid slowly while whisking, keeping the temperature about 35C.
• Leave to set in ice bath.
• Gently break up the gel with the whisk and then sieve through the cheesecloth.

The gel will trap the sediment, but leak liquid.

Does the sediment "settle" at the bottom of the container if you let it sit for a few hours, undisturbed?

If so, it might be an option to use a siphon.

We have one for our beer brewing. It looks like this:

(image from Amazon)

Attach a piece of vinyl tubing to the top and it has a pump action to start the flow. As long as your receptacle is lower than your starting container, you're golden.

But, as I've said, this will only work if the particles settle out of the solution and you have to be very careful not to stir them up when you start siphoning and to cut off the flow before you suck up the particles.

The softer rice is, the easier the mix can be homogeneus. You left it 3+ hours after blending it, other ones left it 1-12 hours before crushing it on a blender. Some use mortar and pestle (There are hardcore ones called "Molcajetes" made of volcanic stone in México).You can even forget about crushing rice when you acquire rice flour instead of simple rice.

If you use boiled rice, instead of the unboiled one, the mix can remain homogeneous easier, and the Horchata will have a nice taste closer to the dessert rice pudding (known in other cultures as simply rice+milk) preferrably adding some milk-related, vanilla flavor or the other ones used adecquately in the dessert. There will be less sediments that way. In fact, horchata can be the answer for when you've made too much rice pudding to be consumed on time.

Alternative uses for remanents are already covered in site.

My method is I COOK the rice, then blend, then sift. The flavor is so much better and creamier and there is NO grit, just a little bit of sediment, which is normal.

Wow I had no idea horchata was so easy! I'm going to try it. Maybe my mead making can come in handy...

• Try adding guar gum. It is like cornstarch, but 8x as strong, so you don't need as much (1/2 teaspoon). It is an emulsifier so it binds fats with water, and thickens up smoothies and lattes. I use it when I make green tea frappuchinos to prevent the milk from separating from the ice water. I don't know if it will work for this as there doesn't appear to be any fats, but it can't hurt and it will definitely thicken it a little.

• To clarify mead, I use bentonite clay and Sparkalloid. One attaches to the to the positive particles, and the other attaches to the negative particles, and they drop out as sediment. After it settles (about a week), I rack it with an auto-siphon (mentioned in another answer) to siphon off the top liquid and leave the sediment behind. I don't know if this will help or hurt you. Cinnamon flavor does not settle out as I use cinnamon flavor in mead too. However it may strip too much of the rice flour out. Try with only the siphon, then with either bentonite, or Sparkalloid, then finally both. You would have to keep it in the fridge long enough to settle (about 4-5 days with bentonite and 7 days with Sparkalloid).

• Strain with a coffee filter after you use your other filter.