what to do with the spent substrate?

Hi Iain,

Good question – we investigated this quite a bit last year. It is possible to make biofuel briquettes from the spent grounds but you need an expensive briquetting/pelletising machine which forms the briquettes or pellets at high temperature and pressure. There is a company in London who have just started doing this on an industrial scale: http://www.bio-bean.com/products/

On a smaller scale, you can make individual coffee logs at home by mixing the dried grounds with another form of fuel such as wax and sugar, in a similar style to this: http://www.instructables.com/id/How-to-make-a-FireLog/

Hope this helps,

Eric

• This reply was modified 10 years, 1 month ago by Eric Jong.

Hi Piers,

Yes it would be worth breaking up and crumbling the coffee/straw mix before mixing if you’re going to make briquettes.

Because of the amount of substrate we deal with at our farm (and the fact we’re in a city centre building where we don’t have space to do much else with it), all our spent substrate goes to a composting operation run by the city centre waste collection service.

It’s a great resource left over at the end of the growing process – let us know how you get on making briquettes 🙂

best wishes, Adam

I’ve seen studies showing that spent mushroom substrate can be used as feed supplement for chickens and cattle but this was when the substrate was straw. I’ve tried offering some spent coffee substrate to pigs and they didn’t seem too impressed! My thoughts are that the coffee wouldn’t be very appetising to them and may make them ill.

Hi Caspar, and welcome to the forum 😉

The strains of Shiitake we’ve tried haven’t liked growing on a substrate high in coffee, however they do seem to like it when used in smaller amounts of 10%-20% of a straw or wood based substrate.

The waste substate definitely makes a nice hot compost pile though – we’ve composted hundreds of kilos of the spent substrate and I’m always amazed at the warmth coming form the middle of the pile, as well as the number of worms living in there during the summer. We’ve had similar thoughts about using that heat to warm a growing space, especially during the cooler months and it’s something we may get to try later this summer when we design an outdoor growing setup.

Let us know how you get on 🙂
best wishes, Adam

Hi Caspar,

I haven’t measured the temperature in there so don’t know I’m afraid..I’d guess it’s at least 50C+

The spent substrate definitely has plenty of energy and heat to give off, but it would be difficult to produce a whole load all at once – maybe more useful as an ongoing additive to an existing compost heap? Do you feed a biomeiler to keep the heat generation going?

We’re going to look at an outdoor setup mainly because have asked about how best to grow outdoors like this on a budget. It’s not the best way to grow mushrooms as it’s more difficult to control the environment, but I think it’d be possible to have fairly reliable production at certain times in the year in a temperate climate.

Best wishes, Adam