Eric's over-the-top home made cheese press

[memkuk]

It's probably an overkill, but it works great: compressed air cylinder provides adjustable pressure. In order not to have to bring the compressor into the house, I converted an old fire extinguisher so it can be pressurized at the compressor and then connected to the cheese press.

Eric.

[Sailor Con Queso]

Looks great Eric. What is the base made of? Looks like granite.

[Cheese Head]

Welcome to the forum Eric, great first post and great looking press, I assume you use the press area divided by the pressure gauge times the pneumatic cylinder area to get the applied pressure.

Base does look like granite, nice grooves for whey to run out through, if making cheddar you could have a lot of pressure/force, hope it doesn't crack that slab.

The old Dutch style hoops were all wooden, but I think closer slots, any concern of extruding sheets of curd out between the wooden slats?

Again great looking build!

EDIT: Just noticed your avatar image, assume that cheese was made in this press, form looks great, slots must be small enough to minimize extrusion. Sorry, didn't mean to be negative, just concerned.

[FarmerJd]

Very impressive! That would double as an apple press. Have you used it on cheese alot so far? I am curious about the cylinder size. What is the bore size and stoke length? John brought up a good point about the base possibly cracking under pressure but a simple solution would be a piece of metal tubing running from side to side underneath that both rods go through (you would have to add some short legs also i guess). I couldn't really see the base well but it looks like you might have counter sunk the bolt heads in the granite. is this right?

I used a piece of Corian counter top (sort of like granite)for my base too because you can router your trenches easily and it is easy to clean. Great idea.

This is the kind of post that I come here for! Seeing other people's ingenuity is a real blessing. Thanks again Eric for posting.

[memkuk]

Sailor, John, FarmerJd: txs for the nice reactions.
The base is indeed granite, made from a high grade leftover piece, using an angle grinder. The slab is 3 cm thick, unlikely to crack under pressure... I think (so far so good). The base rests on 4 little rubber feet, which allowed me to counter sink the bolt heads just a little bit into the granite, so as to safeguard its structural integrity.
The hoop is 20 cm high and has an outside diameter of 20 cm (18 cm inside diameter). The air cylinder has a stroke of 25 cm and a maximum rating of 1 MPa (Megapascal), which is 145 PSI. So far I tested the press up to 60 PSI, but normal usage has been 20 PSI and 40 PSI.
John, to be honest, I don't have a clue how to make the correct calculations for applying the correct pressure. So far I kind of guessed. What is the pneumatic cylinder area in the formula you list in your post? Can you deduce it from the measurements I listed above? Would really appreciate if you could solve this enigma for me.
Sorry for using metric measurements instead of imperial ones: I'm European (Belgian), lost in Asia (Thailand).
The cheese in my profile picture was indeed made using this press and the curds extrusion is minimal, but does give the wheel a typical character.

[Cheese Head]

Eric, from your linked website you don't look so lost, actually look like you are very happy there in Thailand, I especially liked the pictures I presume of you in 70's .

The calculation is basically a ratio. Pressure is weight divided by area, normally measured in Pascals, kPa (kiloPascals or 1000's of Pascals), or MPa (MegaPascals or million Pascals) or in old imperial system mostly only used in US, psi, pounds per square inch. It is pressure that most people use to measure how much load they are putting on their cheese when pressing:

Step #1 - Basic Formula
Pressure On Cheese = [Pressure Pneumatic] x [Area Pneumatic Cylinder] / [Area Cheese]

• Area Pneumatic is area inside your air cylinder.

Step #2 - Convert Area to Formula
Pressure On Cheese = [Pressure Pneumatic] x [π x radius of Pneumatic Cylinder squared] / [π x radius of Cheese squared].

• π is pronounced pi and it's symbol looks more like a double capital t, ie TT.

Step #3 - Simplify Formula
The π's cancel out so we are left with:
Pressure On Cheese = [Pressure Pneumatic] x [radius of Pneumatic Cylinder squared] / [radius of Cheese squared].

• This formula works whether you are using Pa, kPa, MPa, psi or tons, but you have to use the same radius units, don't mix inches and cm.
• Notice that height of cheese hoop or length of Pneumatic cylinder does not enter into the above equation.

Example Calculations
For your example above we are missing the internal radius of the Pneumatic piston, for example calculations, lets assume it is 3 cm internal diameter, thus 1.5 cm internal radius. Therefore:

• Your low Pressure On Cheese was = 20 psi x 1.5 cm x 1.5 cm / 10 cm x 10 cm = 0.45 psi.
• Your high Pressure On Cheese was = 40 psi x 1.5 cm x 1.5 cm / 10 cm x 10 cm = 0.90 psi.

Or if like metric:

• Your low Pressure On Cheese was = [20 psi x 6.895 kpa/psi] x [1.5 cm x 1.5 cm] / [10 cm x 10 cm] = 3.10 kPa.
• Your high Pressure On Cheese was = [40 psi x 6.895 kpa/psi] x [1.5 cm x 1.5 cm] / [10 cm x 10 cm] = 6.20 kPa.

Lastly, instead of finding out the internal radius of your pneumatic cylinder and using the above formula, you could just stick bathroom scales between the granite slab and the follower, apply air pressure and see what reading you get .

[DeejayDebi]

Very nice build Eric! Looks a lot like the apple press Mom had when I was a kid but smaller. I love it!

[FarmerJd]

I spent 15 minutes working on this reply and then saw John's great response. I didn't cancel the pi's out like John did, but I figured this using the inside diameter of the hoop (18cm) instead of outside (20cm). I also assumed a piston diameter of 2.54 cm instead of 3. (Great minds think almost alike John). With that said here is the post:

I actually I think you have to have the bore or cylinder diameter to figure your pressure or at least that is how i do it. It looked like about a 1 inch cylinder so if that's right the area would be:
 .5 in = radius of cylinder
Area = 3.14(pi) x .5 in (radius) x .5  in (radius) = .785 square inches

Next you multiply this area by the pressure you put on it : 60 psi  x  .785 sq in = 47.1 pounds

Then you have to divide this weight (47.1 lbs) by the area of your hoop:

Diameter of hoop = 18 cm or 7.1 inches  which means radius is 3.54 inches

Area of hoop = 3.14 (pi)  x 3.54 (radius)   x 3.54 (radius)  =  39.3 square inches

Pressure on cheese = 47.1 / 39.3 = 1.19 psi on the cheese.

If you go back and replace 60 psi with 145 psi ( the max pressure)  you get 2.9 psi on the cheese.

Several disclaimers: I do not know the actual piston bore size so that would change everything.
Second, I taught math and physics for 13 years and I hope i didn't insult anyone's intelligence with all the details. I also could be very wrong and don't mind getting called out on it. I am sure others on here are better qualified to explain it. Third, I think the way you made the hoop with the open slots on the sides makes it much different than a simple solid hoop. This makes it much easier for the whey to leave; even more so than with the weeping holes and since the slots go all the way to the bottom you can still slide the cheese out even if it protrudes some. I may try to make one of those myself.

One other thing is that if you used a hoop that was only 12 cm in diameter instead of 18 cm,  the max psi would jump to almost 10 psi on the cheese. Just another thought.

[memkuk]

John & FarmerJD - Txs so much for your extensive explanations. I'll have a look at it again tomorrow morning (it's almost midnight over here...). From a quick reading I gather that I put way too little pressure on my cheese. What I did until now was: when the recipe calls for 40 PSI pressure, I just converted it to MPa (MegaPascal), which is the scale on my pressure gauge, so I ended up putting a pressure of only 0.28 MPa. If I understand it right, I have to make a different calculation for each kind of hoop I use (since I also have a plastic tube type hoop of lesser diameter). BTW, the inside diameter of the pneumatic cylinder is 20 mm (2 cm). I'll make the calculations tomorrow after my first coffee.
John - pictures are from the 70-s and some from the 80-s. I aged like a Blue cheese, while my wife aged like a smooth Gouda.
FarmerJD - indeed, the cheese slides out nicely, even with the curds protruding a tiny bit. It actually looks nice.

[Cheese Head]

Farmer, indeed great minds think alike , we have same formula/method, different answer as we guessed at different bore of pneumatic cylinder.

Eric, many professional recipes call for pressures which are I believe their pneumatic pressure and assume a certain size mold. They are not the applied pressure on the cheese. For example your 20 cm diameter cheese has a top surface area of:
3.14 x [10 cm / 2.54 cm/in] x [10 cm / 2.54 cm/in] = 48.67 in2

Therefore if you wanted to apply the 40 psi you mentioned to that whole cheese surface area would require 40 x 48.67 = 1947 pounds, the equivalent of a small car! That would easily break your granite base .

I don't know what cheese type you are making but I'm sure members here will have lots of opinions on it if you want to start a new thread on that subject.

Great press, beats the socks off my simple stepladder press !

[memkuk]

Silly me! Tropical morning freshness cools my brain and makes me realize that I misled both John and FarmerJD.
I totally misread the Gouda recipe in the book "Cheesemaking made easy". The recipe calls for 20 and 40 pounds pressure, not PSI... How embarrassing!
But I'm still not out of the woods: the Gouda recipe on this site (CheeseForum.org) calls for "5 pounds per 1 US gallon / 1 kg per 1 liter of milk" for the first pressing and "12 pounds per 1 US gallon / 1.5 kg per 1 liter of milk" for the second pressing. What does this translate to when making batches of 10 liters of milk with the press I have? In other words: what should my pressure gauge read, knowing it goes from 0 to 1 MPa?
BTW, John's and FarmerJD's formulas will still come in handy for some other non-cheese related projects, so txs for the lesson.

[memkuk]

After the second cup of coffee I tried to resolve the enigma myself. I came to the following conclusion, primarily using FarmerJD's reasoning as outlined in his post:
Pneumatic cylinder bore = 2 cm, which equals 0.78 inch, hence the radius is 0.78 / 2 = 0.39 inch.
Pneumatic cylinder area = 0.39 x 0.39 x 3.14 = 0.47 square inch.
When I applied 0.28 MPa (= 40 PSI) pressure on the cheese, it was the equivalent of  putting a weight of (40 PSI x 0.47 squ in =) 18.8 pounds on it.
It looks to me now that this is how far I have to take it, no further calculations needed.
It also means that the pressure I used was too low: if the recipe asks for 20 pounds pressure, I should have used 0.3 MPa (43.5 PSI), since 43.5 x 0.47 = 20.4 pounds.
If the recipe then asks to increase the pressure to 40 pounds, my pressure gauge should read 0.6 MPa (87 PSI) which will give me a pressure of (87 PSI x 0.47 sq in =) 40.8 pounds.
BTW, I use a converter program to calculate MPa to PSI and vice versa.

FarmerJD - did I do my homework correctly? Please let me know if all this makes sense: I used to be good in languages, but math was not my strongest subject.  :'(

[FarmerJd]

Your math is right and if that is what the recipe means, you are on the right track. However, I am not sure your understanding of the recipe is right. Did the recipe specify a cylinder size? If not then you can't be sure of the needed pressure. Pressure is measured in psi not lbs. This has always irked me about recipes. I for one do try to go by the numbers given in the commercial recipes. In my cheddar recipe for instance i press at 2, 6, and 20 psi. As John mentioned this means huge numbers on the larger hoops. I am currently looking at a way to do this more effectively. I looked at making a press just like yours but with a 4" piston diameter. These are hard to find and expensive if bought new. I just recently came up with a new idea that I am going to try using a suspension air bag.

The bottom line is that I don't think you can put too much pressure with your press on a 18cm hoop. I would start with a fourth of the max pressure for 15 min and then work up to as much as I could.

John, I read your comment on the commercial recipes. I have read somewhere that there is a tool for measuring pressure within the cheese as it is being pressed. Have you heard of this and if this is the case it seems to support the idea that the pressure number is not just for the machine but is the actual cheese pressure. I really want to answer this question. Especially before I go to the trouble of building a new press for my 12 inch stainless steel hoop! 

Eric I hope i helped. If that didn't make sense let me know.

[memkuk]

You sure helped. A fourth of the max pressure, then up to max: I think that's what I will do in the future. Good to know that I don't have to worry about the maximum pressure with my setup: until now I was afraid that I would press the cheese too much.
A big txs to Farmer and John.

Farmer - Looking forward to hearing/seeing more of the new press you are planning to build.

[wharris]

Eric, 

That is a truly beatiful press.  Well done.

John and Farmer, Very nice and well thought out responses. I'm completly diggging the math. It drives me absolutly crazy to see cheese recipes that do not specify a hoop diameter yet calling for 20 lbs of weight.

Eric,

What are the specs on that cylinder?