PSI per style

[FarmerJd]

You calculations are correct. Lots of other variables involved in getting the curds to knit (curd temp, length of pressing time, etc.) but obviously pressure is an important one. That weight may seem unmanageable but with a press with a levered arm and pulleys that weight may be reduced by a factor of 10 or more. Right now I am getting 15-20 psi on a 10 inch hoop (more for my 8" and less for my 12"). My press has a mechanical advantage of 4. I put between 300 and 400 lbs on it. Over 300 is downright scary to be honest especially when it starts creaking.

[Sailor Con Queso]

You're calculations are a little off. I have attached a PSI Calculation  spreadsheet that should help.

That being said, bear in mind that the U of Guelph's procedures and recipes are geared for large scale commercial production. From a practical level spring type presses for the home cheesemaker can really only handle 50 pounds. After that the spring bottoms out and you start bending metal pieces. That is why many recipes like Ricki Carrol's don't tell you to press at more than 50. Even on my big lever presses, I almost never go over 10 psi.

Pressing longer may work, but that also allows your cheese to build up too much acid. On a 4" hoop, I would shoot for 100# if you can, see how it works and go from there. If you don't get a perfect knit, it's not the end of the world.

[FarmerJd]

You're calculations are a little off. I have attached a PSI Calculation  spreadsheet that should help.

Not sure what you see Sailor. It appears to line up with the chart you posted to me.

If you don't get a perfect knit, it's not the end of the world.

Agreed.

[Sailor Con Queso]

It's really close to my chart. Just being a little anal.

I see a trend among the group where several people seem to want to see just how much pressure they can apply to their cheeses. Overkill IMHO. For me the point of PSI is consistency, not mashing cheese into pancakes, just because you can. If you get a good knit and remove the excess whey, that's good enough. If you aren't getting a good knit on Cheddars, etc, increase the PSI and/or look at some other solutions. JD - in your case, you know you need that kind of pressure with your bigger wheels but not everyone need to use 300 pounds.

I feel that pressing time is sometimes more important than actual weight or pressure. When you press an unsalted cheese for too long, residual whey remains, the bacteria can continue converting lactose, and you can end up with an acidic and/or dry cheese. It's all about balance. If it ain't broke, don't fix it. In my case I have to look at techniques where I can produce the same quality cheeses consistently.

[FarmerJd]

Good point about consistency. That really is the goal. I know it may seem like folks are overly "psi happy" but there is a lot of difference between a 6" and 8" cheese (almost double the pressure required) and I think sometimes folks don't realize how much more weight it takes to stay consistent. It is a big jump for home cheesemakers from 6" to 8". Everybody wants a big wheel but it requires a different setup not just a bigger hoop and more milk. BTW, did you get my stuff?

[Sailor Con Queso]

Absolutely. There is a HUGE difference between a 6" and an 8" hoop. On my setup with 8" Tomme molds I press with 125 pounds (~2.5 psi) for "light", 250 pounds (~5 psi) for "medium" and 375 pounds (~7.5 psi) for "firm". Unless something goes screwy during a make, I rarely press any heavier than that.  My only regular exception is Cantal which I still only press at 10 psi. To me 20 psi is just not necessary.

There are other ways to encourage a good knit. For example with Cheddar the curds can really cool down quickly during the milling process. One option is to throw the curd back into the pot and warm them back up before hooping. Or put the curds in the hoop and put the entire hoop back in the pot. If milling takes a long time, the pH can drop significantly (an additional .2) before salting. I mill by hand and it takes me about 45 minutes to process a 35 gallon batch. That's 45 minutes of additional acid production. I find that a pH that is too low seems to resist a good knit. For that reason, I drain and cheddar a little earlier so that it is not over acidified at salting. Normal drain for Cheddar is around 6.1. I drain at 6.2-6.3 to compensate for the long milling time.

[OudeKaas]

Well, I am appreciating all of the well-informed participants here, and while my first reaction to the PSI discussion was, ugh, math, I am feeling much better about it now. It's clearly the right way to look at pressing needs accurately independent of cheese size.

I managed to get up to about 140 lbs in my wacky stacked pressing scenario, so for a 4.5" diameter mold I figure that's about 8.75 PSI, which I held for 24 hrs after some time building up to it. That will have to do, and based on looking at the exteriors, everything seems very well knit together and quite smooth. There are some very faint translucent white lines just barely visible here and there that look like they might have once described curd boundaries, but they are near-nonexistent.

Looking forward to seeing how these turn out . . .

[OudeKaas]

Here's a pic of the cheeses just before bandaging. I can see on the right one that I used too much folded-over cheesecloth when pressing, and on the left you can see the light tracery of white lines (I wonder if I might have not mixed the cheese salt in well enough before pressing and that might account for them?)

[FarmerJd]

They look great. If the wrinkles bother you, you can take the cheesecloth off after pressing and lightly press for 30min to remove the wrinkles. I just let it go. After aging it isn't noticeable.

[wharris]

Absolutely. There is a HUGE difference between a 6" and an 8" hoop. On my setup with 8" Tomme molds I press with 125 pounds (~2.5 psi) for "light", 250 pounds (~5 psi) for "medium" and 375 pounds (~7.5 psi) for "firm". Unless something goes screwy during a make, I rarely press any heavier than that.  My only regular exception is Cantal which I still only press at 10 psi.

Yes, I am very bored here in my hotel, and felt like making graphs.

[susanky]

I'm sorry you are bored.  But grateful for the graphs!  I've save them for future reference.  Thanks for your efforts.  They were not in vain.
Susan

[FarmerJd]

Yes, I am very bored here in my hotel, and felt like making graphs.

LOL. Boredom is the mother of great graphs.

[Boofer]

Yeah, who knew back in high school that math would make cheese making so neat. Thanks for being bored, Wayne.

-Boofer-

[wharris]

Thought occured to me to just include the Excel file that I used to make these.
You can put whatever PSI in you like and make your own chart.

pm me if you have questions.

[zenith1]

very nice work with the chart Wayne. Which version of Excel did you use?