What can I make instead of buttercream to practice piping?

It depends on what you want to pipe.

If you want to pipe designs that have more details e.g. flowers, stars, it is best to use a buttercream recipe that has at least 50% shortening. You can google for decorator's buttercream, which works well for this. Shortening makes the buttercream stiffer and more able to withstand humidity, and so the designs will hold their shape and turn out well.

If you only need to pipe lines, words, simple swirls, you can use fresh whipped cream (just whip some really cold whipping cream). Melted chocolate will be fine too, but you need to work fast because it might harden quickly.

This sounds crazy but you can use toothpaste to practise piping lines and words. Just squeeze out some to your piping bag attached with piping tip. If you do on a clean surface, you can scrap them back to a container and still use it after practicing without wasting, and you won't eat it :)

extremely tough matter. query into a search engine. that could actually help!

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you can try CHOCALATE.MMMMMMMMMMMM CHOCALATE