Comparative Relative Humidity Table

[wheels]

I've made up a table, from an online relative humidity calculator, showing the amount of water in the air at different RH and Temperatures:



The different colours link the humidity and temps where the amount of water in the air is the same.

Where it gets us to know that there's the same amount of water in the air at 12C/75RH as at 15C/62RH is probably for cleverer people for me to work out. However, it goes to show that there's one heck of a diiference between a curing chamber at 12C and 75% RH and one at 15C with the same RH.

Anybody got any thoughts on it?

Phil

[grisell]

That's a nice table!

I'm not sure how it would help us, though. To me, it seems that it is the relative and not the absolute humidity that matters.

Take an example: In Gothenburg, Sweden, it's now 0.4 C and 62% RH which amounts to 2.67 g water vapour per kg air. In Khartoum, Sudan (a very warm place), it's now 28 C and 14% RH which amounts to 3.37 g water vapour per kg air. That's more than in Gothenburg. If you hang out your washing, would you expect it to dry sooner in Gothenburg than in Khartoum?

If that were the case, we would dry our washing in the refrigerator instead of in a drying cupboard.

[grisell]

- but I'm far from certain. I might be mistaken here.

[wheels]

Please look again - you've completely missed the point.

added: Ok that's a bit blunt but If you read what I wrote, I'm talking about different temps but the same RH. That would mean that the amount of water in the air in Khartoum would be 14.92g/kg.

So there would be 5 times the water around the salami to cause problems even though it would (presumably) dry more quickly.

However, I would suggest that we keep the discussion in the real world - our adapted fridges are all within similar defined temps - whilst ambient temps may have an effect, the internal ones are all similar.

[grisell]

Obviously. What is the point? I mean, it's nice to know that air at 11 C, 80% RH contains the same amount of water as at 15 C, 66% RH. Is it that you will use the table to see how much RH goes up if the air is cooled a certain number of degrees? In that case I understand. But does this have anything to do with how fast a product dries or the risk of case hardening? That was my point. And it's a question, not criticism.

[wheels]

Nah - let's not bother eh.

[BriCan]

Please look again - you've completely missed the point.

That would mean that the amount of water in the air in Khartoum would be 14.92g/kg.

I must be sicker than a dog

Just read this and this part jumped out at me: ----- we cannot die of thirst in the desert as there is water in the air all we av to do is find a way to get it.

I know, I will get my hat and a hot toddy.

[wheels]

Poor old Brican, if only I could send you a bottle of the Wychwood Brewery Beer that I'm just drinking.

[BriCan]

Poor old Brican, if only I could send you a bottle of the Wychwood Brewery Beer that I'm just drinking.

Hope U did not put it on my slate


Question? if I am @ 1degree C with 78% humidity how much water have I in the air??

This is (for me) ideal for (walks lightly -- egg shells) producing 'good' mould in my cooler/fridge.

Thoughts??

[wheels]

I know, I know, and why do I bother? But, believe it or not, it's part of my mission to try to be able to provide people with simple ways of achieving quality products without having to become anally retentive idiots like us!

Phil

[mattwright]

my head hurts. I get the science behind it... well, OK actually I don't - but the table is interesting.

I think I need to see some real world practical examples though.. If anyone has two curing chambers, and wants to cure something at different temps but the same %RH, and then see the difference - maybe the importance of this will mean more to me.

So should we be using an even higher humidity if the temps are lower? my brain sure does hurt.

[wheels]

Matt

So does mine - big time!

I posted this to stimulate debate, not to say "I know the answers". I'd really welcome your thoughts.

If successful drying is about the moisture in the air being a little bit below the Aw of the salami, what does this mean?

If mould formation is affected by the amount of water in the air, what does this mean?

Does it explain why drying to Adam Marianski's regime (higher temps and RH than you lads would use) leads to more chance of mould? I'd hate to suggest so as he's so much more experienced than we are.

Logic dictates that the more water there is in the air, the more chance there will be of mould development, but it's the correlation between the air and temp that's the answer, I'm sure.

If we can fathom that out, we'll be all the wiser.

Phil

[mattwright]

right now I am curing at about 50F (10C) and 80% humidity. I have some air flow in my chamber. It seems to be OK for most stuff. I am still nervous about doing a really thick piece of meat, like a whole leg however.

Who knows... This isn't usually my view, but strangely it is this time: people for centuries have cured meat without knowing much about rH at different temps... I am really going by look and feel for me.

I am curing now at lower temps than I have ever traditionally done - I am normally around 55F (12.7C) but I have noticed that I don't ever get bad mold now with the lower temps.

Is this a function of the lower temp, or now obviously lower water content in the air around the salami? Is it because my chamber is inoculated with great mold at the moment?

It is just working well for me, that is all I can say

I just learnt today that there is a risk of listeria and staph in finished products if you hang wet ones next to them, and that is obviously a problem for the USDA.. so that has turned my plans around a bit... and now your relative humidity table? BAH... I need a Scotch

[grisell]

[---]

Who knows... This isn't usually my view, but strangely it is this time: people for centuries have cured meat without knowing much about rH at different temps...
[---]

Yeah, but I bet a lot of them failed, too.

[grisell]

I have now talked to a meteorologist at the Swedish Meteorological and Hydrological Institute.

According to him, only the relative and not the absolute humidity (the absolute amount of water in the air) plays a role in the drying rate. If the temperature is raised to a point near the boiling point of water, the evaporation rate must be taken into account, but that effect is totally negligible in our temperature range.

We can thus establish that drying at e.g. 75% R.H. is as efficient at 1 C as at 20 C and concentrate on the temperature instead. Temperarure will affect the rate of chemical and microbiological changes.

However, wheels' table is interesting as it shows how much tempertaure affects the relative humidity in a closed chamber.