Grinding Seeds at Home: Blender, Coffee Grinder or Mortar and Pestle?

Some seeds, such as flax, are far more useful once ground. Others, like cumin or coriander, taste stronger and fresher when you grind them yourself. The tool you pick makes a difference to the texture and to the mess, so here is a plain-English guide.

Why grind at all

Whole flaxseeds often pass through the body largely intact, which means you miss out on much of what is inside. Grinding breaks the hard shell. For spice seeds, grinding releases aromatic oils, and pre-ground spices lose their punch within months. Ground chia, sesame and sunflower seeds also blend more easily into batters, porridge and smoothies.

The coffee or spice grinder

A small blade grinder is the best all-round tool. It gives a fine, even powder in 10 to 20 seconds. Work in short pulses and never run it for more than 15 seconds at a time, because friction heats the seeds and turns the oils into paste. Keep a separate grinder for spices if you can, or clean it by grinding a spoonful of dry rice and wiping it out.

A few tips:

Fill the grinder only a third to half full.

Shake it between pulses so the seeds near the lid fall down.

Tip the powder out and let it cool before storing.

The blender

A high-speed blender handles larger amounts, such as 1 cup of flaxseed, better than a small grinder. Use the dry container if you have one, or a narrow jar. Pulse a few times, then blend on high for 20 to 30 seconds. The blender gives a slightly coarser meal, which is fine for baking and porridge.

Avoid blending very small quantities, since seeds will spin under the blades and never get hit. Add at least 1/4 cup.

Mortar and pestle

A mortar and pestle is the oldest tool and the best for spice seeds. It crushes rather than slices, and you can stop at any texture, from rough crack to fine powder. It is slow for hard flax, and it is not ideal for big batches, but for toasted cumin or coriander it gives lovely flavour. Add a pinch of salt to stop seeds from skittering out of the bowl.

Storage matters

Ground seeds spoil faster than whole seeds because more surface is exposed to air. Store ground flax, chia and sesame in an airtight jar in the fridge for up to a month, or in the freezer for several months. Ground spice seeds are best used within a few weeks. If a ground seed smells bitter, sharp or like old paint, discard it.

A good routine is to grind a small amount each week, rather than a huge batch once.

If your powder turns into a clumpy paste, the seeds were too oily, the grinder ran too long, or the seeds were damp. Stop, chill the seeds for ten minutes in the freezer, and try again with short pulses. Paste can still be used as a seed butter.

Who should check first

Ground flax and chia absorb a lot of liquid, so drink water alongside them. If you take blood thinners, are pregnant, have kidney disease, or have a digestive condition, check with a doctor before adding ground seeds daily. Anyone with a seed allergy should avoid the seeds they react to.

This article is general information, not medical advice.