Quality and Lab Testing

What we test for

Every batch is screened by an independent laboratory that we do not control and do not have a commercial relationship with. The panel covers the things that actually matter for a substrate people handle and then compost into their gardens.

Heavy metals

Lead, cadmium, mercury and arsenic. These are the concern with any agricultural byproduct, because plants pull metals out of soil and concentrate them. Our substrate is hardwood sawdust from untreated lumber and wheat straw from food-grade grain farms, and the test panel confirms that neither is carrying a heavy metal load.

Total plate count and coliform

Total plate count measures the total bacterial load; coliform tests look for the faecal contamination markers that indicate an unsafe handling environment. Both should be at or below the limits set for the substrate class. A high plate count is the single best predictor of whether a block will contaminate before it reaches a customer, which is exactly why we test for it.

Pathogens

We test for Salmonella, E. coli and Listeria. These are present in raw agricultural by-products and are removed by pasteurisation, so this panel verifies that the heat treatment actually worked rather than taking it on trust.

Mould and yeast

Total mould and yeast counts, plus a species-specific look for the aggressive competitors: Trichoderma, Aspergillus and Penicillium. These are the organisms that ruin home grows, so knowing the count is low before shipping is worth more than any instruction we could print.

Moisture and pH

Not a safety test, but an integrity test. Substrate that is too dry will not colonise properly and substrate that is too wet will anaerobically ferment. The pH matters too, because it determines which organisms can compete with the fungus.

How we publish the results

Every batch gets a Certificate of Analysis. You can find yours with the batch code printed on the side of your carton. We publish the reports for the batches that failed as well as the ones that passed.

We publish the failures for a practical reason. If your block does not grow and you check the report and see a high plate count, you have your answer immediately. If we only published the good batches, you would spend three weeks wondering what went wrong, and we would spend three weeks not knowing either.

The two-week quarantine

Every colonised bag goes into a fruiting room for two weeks before it is boxed. This is the step that separates a reliable block from a hopeful one.

During quarantine we watch for the three things that indicate a problem: off-odour, discolouration of the substrate, and any growth outside the bag. A block that is going to contaminate almost always shows it during this window. Catching it here means it never reaches a customer - and it means the batch code on your carton corresponds to a block that was inspected, not just one that was manufactured.

How to read your certificate

Find the batch code

It is printed on the side of the carton, along with the species, the harvest date and the substrate weight. It looks like GWM-2411-PO-03: batch, year-month, species, line.

Match the species

The species code in the report must match the species on your carton. If it does not, you have the wrong report - contact us and we will send the right one.

Check the dates

The substrate preparation date, the inoculation date and the harvest date should all be in the correct order and consistent with a two-week-plus colonisation and fruiting cycle. We have never had a falsified report and we have never found a reason to create one.

Look at the trend, not just the number

One batch can be higher than another without either being a problem. What matters is whether your batch is within the limits we consider acceptable. If you want to know what we consider acceptable for each species, the limit column on the report tells you.

Our own standards

The regulatory limits are floors, not ceilings. Our internal limits are stricter than the published standards on the two panels that correlate most strongly with success: total plate count and total mould. A batch that passes the legal test but misses our internal threshold does not ship.

If something is wrong

Send us a photo and the batch code. If the block contaminated in a way the report should have caught, that is our failure and we will tell you so plainly, publish the corrective action we took, and replace your block. If it went wrong because of how it was handled, we will still replace it under the 90-day guarantee - but we will also tell you what to adjust, because we want the next one to work.