GUIDE
Freeze drying yield: measure it per product, not per batch
Yield is the share of what went in that came out: net dry weight divided by net wet weight. It is the number that turns a wet price into a finished price, decides which products are worth a machine's time, and tells you when a run has gone wrong. And on most runs, the way it is usually measured makes it useless.
The problem with one number per run
A run rarely holds one product. Three mushroom varieties across seven trays is an ordinary week. Weigh the whole load going in and the whole load coming out, and you get one yield for the run. Say the run held oyster mushrooms and lion's mane: oyster dries down to 17%, lion's mane to 10%, and the run as a whole reports 12%. That 12% is not true of anything on the trays. Price the oyster from it and you undercharge; price the lion's mane from it and you overcharge; compare this week's run to last week's and the difference is mostly which product had more trays.
The fix is not more weighing. Everything needed to split the run by product is already on the trays. It only has to be recorded per tray instead of per run.
What to record
Three things per tray, two of them before the run starts.
- Product. What is on this tray. Mixed trays defeat the split.
- Tare. The empty tray, plus a mat or liner if one is used. This gets subtracted from both the wet and the dry reading, so the yield is of food rather than of stainless steel. Trays are not all the same weight, so weigh each one once and keep the figure.
- Wet weight, then dry weight. The loaded tray going in, and the same tray coming out. Per tray, not the whole load together.
A worked example
One tray of oyster mushrooms. The tray weighs 680 g and the mat 40 g, so the tare is 720 g.
| Reading | Scale | Less tare | Net |
|---|---|---|---|
| Wet, going in | 1,520 g | 720 g | 800 g |
| Dry, coming out | 856 g | 720 g | 136 g |
136 g out of 800 g is a 17% yield for that tray. Do the same for every tray, add the nets together by product, and the run splits itself.
| Product | Trays | Net wet | Net dry | Yield |
|---|---|---|---|---|
| Oyster | 2 | 1,600 g | 272 g | 17% |
| Lion's mane | 5 | 4,000 g | 400 g | 10% |
| Whole run | 7 | 5,600 g | 672 g | 12% |
The whole-run figure is still there, and it still adds up, because the products were measured against the same final reading. It just is not the number that anything should be priced from.
Why tare is not optional
Skip the tare and both readings carry 720 g of tray. The oyster tray above would report 856 g out of 1,520 g, a 56% yield, which is flattering and false. Worse, the error is not consistent: a lightly loaded tray is mostly tray, so its yield is inflated more than a full one, and two runs of the same product stop being comparable. Weigh every tray and mat once, write it down, and subtract it every time.
What the split tells you
Once yield is per product, the questions that matter get answers. Which product is worth a full machine, and which is only worth the spare trays. Whether this supplier's fruit is wetter than the last one's. Whether a machine is drying to the same endpoint it did in the spring. And, combined with what each tray cost, what a finished gram of each product actually costs, which is the subject of the companion guide, how to calculate cost per gram for freeze dried food.
FreezeDry HQ keeps the product, tare, and wet weight on each tray of the prep sheet, reads each tray separately at check-in, and reports the yield per product for every run, on every plan. It is the same arithmetic as above, done every time without the spreadsheet.
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