[mikka]

Hi everyone!

I hope nobody minds me asking this question here, if I have broken any rules I apologise.

I am working with quite a cool startup company and we are using freeze drying for vegetables and meat. My question relates to detecting over temperature during processing. We have temperature probes in the ingredients during the drying process however I am wondering if we could get more accurate data on our process control.

The issue with freeze drying is uneven rates of drying causes smaller pieces of product to dry faster or edges of pieces to be at higher temperatures than deeper in to the particle where the probes typically sit. We are trying to limit product temperature to 50ºC but during primary phase (start of process) whilst the product contains ice we apply up to 130ºC. Then as the sublimation rate slows and product temperature rises we reduce heating plate temperature to limit product temp. to 50ºC.

Are there any gases we could measure for during freeze drying to detect burning / charing?

We have thought of C02 but apparently water vapour would interfere with the measurement using FTNIR. I'm not sure if this is correct but it was one opinion from a  chemistry PhD.

Thank you for any help and once again I hope I am OK to ask my question here

[Enthalpy]

Hi mikka, welcome here!

Smell sensors exist as semiconductor chips. Maybe some fit the odour you seek. They work at room temperature so they need a trunk to cool the sniffed gas.

What about detecting the smoke? In vacuum, any light absorption must be attributable to smoke, so you can detect very little smoke, hopefully early enough for your use. At least, that's simpler than identifying a specific molecule. As an alternative to absorption, you could look for light diffusion. If you can see with your eyes ever so little smoke early enough to protect your products, a proper optical means can detect it too.