Is a higher CFU per gram always better?

No. CFU per gram is a concentration, and what reaches the sludge is concentration multiplied by the weight applied. A lower-concentration product applied in greater quantity can deliver more organisms than a higher-concentration one applied in a small quantity, so the headline number can mislead. Concentration is one input to the delivered quantity, not the whole of it.

Why does the end-of-shelf-life count matter more than the count at manufacture?

Because viable counts decline in storage, and an operator often applies product a year or more after it was made. The count at manufacture describes the best case on the day of production; the guaranteed end-of-shelf-life count describes what is actually applied later. Ask for the second figure in writing, since almost nobody in the category volunteers it.

What does a cell count not tell you?

It says nothing about which species are present, which enzymes they produce, or whether the organisms survive the descent to the sludge blanket. Two products with identical counts can behave very differently. Use the count to screen out the obviously weak, then ask the questions the number cannot answer.

What CFU per gram tells you

How to use a cell count without being misled by it: why organisms delivered is concentration times dose, why the end-of-shelf-life figure matters more than the one at manufacture, and what a count cannot tell you at all.

The short answer

CFU per gram — colony-forming units per gram — is a concentration of viable organisms, and on its own it is a weak guide. What actually reaches the sludge is concentration multiplied by dose, so a lower-concentration block applied by the pound can deliver far more organisms than a high-count tablet applied by the ounce; the headline number can mislead in both directions. Nearly every count in this category is measured at manufacture, yet the figure that matters to an operator is the guaranteed count at the end of shelf life, because viable counts decline in storage. And a count says nothing about which species are present, which enzymes they produce, or whether the organisms survive the descent to the blanket. Use it to screen out the obviously weak, not to pick a winner.

What the number is

CFU per gram — colony-forming units per gram — is a measure of concentration: how many viable organisms sit in each gram of product. It is a real and useful figure, and it is also the most over-read number in the category. On its own it does not tell you how many organisms will reach the sludge, how long they will remain viable, or what they will do when they get there. Treating a high concentration as a proxy for a good product is the mistake this page is meant to head off.

Organisms delivered is concentration times weight

What reaches the sludge is not the concentration but the quantity of organisms delivered, and that is concentration multiplied by the weight applied. A worked example makes the point, and the figures here are illustrative arithmetic rather than the specification of any SediLogic product. Suppose a tablet is sold at ten billion CFU per gram and applied at five ounces, while a block is sold at four billion CFU per gram and applied at thirty pounds. The block carries the lower headline concentration, yet far more of it goes in, so it delivers far more organisms. The bigger number on the tub can be the smaller delivery.

	High-count tablet	Lower-count block
Concentration	Ten billion CFU/g	Four billion CFU/g
Application weight	Five ounces	Thirty pounds
Organisms delivered (relative)	Fewer	Far more

Illustrative arithmetic, not product specifications.

Read the table by its bottom row. The concentration is the marketing headline; the organisms delivered is what the sludge actually sees, and it depends as much on how much product is applied as on how many organisms are in each gram of it. A cell count quoted with no application weight beside it is only half of a figure, and the half that is missing is often the half that matters.

At manufacture, or at the end of shelf life

There is a second trap in the number, which is when it was measured. Nearly every count in this category is taken at manufacture, and almost nobody states a guaranteed count at the end of shelf life. Yet the end-of-shelf-life figure is the one that matters to an operator, who may be applying product a year or more after it was fermented. Viable counts decline in storage, so a figure taken on the day of manufacture overstates what actually goes into the lagoon later. A count with no date attached quietly assumes the best case.

What a cell count cannot tell you

Even a perfect, end-of-shelf-life count is silent on the things that decide whether a product works. It does not tell you which species are in the blend, which enzymes they produce, or whether the organisms survive the descent through the water column to the blanket. Two products carrying the same count can hold different organisms doing different work, and the number on the label distinguishes neither. This is why a count belongs in a screening role and not a deciding one.

How to use the number well

The sensible use of a cell count is defensive. It will help you screen out something that is obviously weak, and it will not, on its own, identify a winner. Ask for the concentration and the application weight together, ask for the guaranteed end-of-shelf-life count in writing, and then ask the questions a count cannot answer: which species, which enzymes, and what evidence there is that the organisms reach the material. A supplier who can answer those is telling you more than any single headline figure can.

References

MDPI Applied Sciences (2026). Physicochemical determinants of storage stability in spore-based bacterial biopreparations. Applied Sciences (MDPI).Peer-reviewedViable counts decline in storage, so an at-manufacture figure overstates what is applied later.
Genesis Biosciences. Bacillus strain validation and whole-genome characterisation. Genesis Biosciences (manufacturer).Vendor-published

Common questions

Is a higher CFU per gram always better?: No. CFU per gram is a concentration, and what reaches the sludge is concentration multiplied by the weight applied. A lower-concentration product applied in greater quantity can deliver more organisms than a higher-concentration one applied in a small quantity, so the headline number can mislead. Concentration is one input to the delivered quantity, not the whole of it.
Why does the end-of-shelf-life count matter more than the count at manufacture?: Because viable counts decline in storage, and an operator often applies product a year or more after it was made. The count at manufacture describes the best case on the day of production; the guaranteed end-of-shelf-life count describes what is actually applied later. Ask for the second figure in writing, since almost nobody in the category volunteers it.
What does a cell count not tell you?: It says nothing about which species are present, which enzymes they produce, or whether the organisms survive the descent to the sludge blanket. Two products with identical counts can behave very differently. Use the count to screen out the obviously weak, then ask the questions the number cannot answer.

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