Pressure cookers are used in mushroom growing as a way of sterilising agar, liquid culture, grain, tools, and substrates. The reason we sterilise our substrates and tools is to prevent contamination from taking over our grow. By sterilising, we are creating a perfect environment for all Fungi, not just the ones we’re trying to grow. You can think of it like weeds in a vegetable patch. We only want to grow our target species. The other species will compete for resources and possibly be parasitic. They could even be dangerous for us.
The sterilising process kills off all bacteria, fungi, and spores so that our mycelium can colonise and thrive in its substrate in an uncontested way. For more information about the different types and styles of sterilisation and pasteurisation that are used for mushroom growing, you can read my blog here where I explain the various sterilisation and pasteurisation treatments used for mushroom growing substrates.
Today we will look at the best pressure cookers for mushroom growing, in my opinion. Our goal is to achieve textbook sterilisation which requires a temperature of 121C through the medium i.e., grain, substrate, agar, or liquid culture. This can only be achieved by artificially increasing the environmental pressure, causing water to boil at a much higher temperature. As an example, on Everest, water boils at around 71C while it would boil at around 500C at the bottom of the Mariana Trench. It’s also why in space, where there is no pressure, the boiling point of water would be so low the water in your body would begin to boil off.
The way I see it, there are 4 main ‘brands’ of pressure cookers available to the majority of mushroom growers. I’m deliberately excluding autoclaves from this review, as I will write another post further down the line on this topic. An autoclave is a purpose-built steriliser ranging in cost and complexity, but at the minimum have their own internal element and a pressure gauge. In this blog post, PC will be used as an abbreviation of pressure cooker and pressure canner as these two names are used interchangeably.
These kinds of pressure cookers are available from supermarkets, kitchen stores and online platforms. They vary in size and price depending on the brand and are most commonly made from stainless steel or aluminium. I won’t be reviewing a single PC in this category because they all achieve the same goal fairly consistently. I’ve used, abused, destroyed, and lost more of these PCs than I care to admit. I no longer own one but I’ll link to some generic models on Amazon and eBay so you can take a gander. The primary objective when buying a PC is to find the widest, tallest one you can. This will give you the greatest range in use and what you can load it with.
These PCs are generally inexpensive, readily available, and perfectly suitable to use in mushroom growing, however, not all of these PCs reach 15psi, in fact, the vast majority don’t. They top out at around 7 to 8psi so it’s worth speaking to the manufacturer to find the exact specs. This isn’t a problem as you can run them for longer to achieve sterilisation using the chart below as a rough guide.
The smaller, budget PCs seldom include a pressure gauge, have spare parts that are difficult to find as they’re often only produced in batches then the model is discontinued. This is because it’s not in the manufacturers interest to build products that last or can be repaired, rather to get you to buy a newer version further down the line. The majority of these PCs don’t feature a rocker, meaning they build pressure and vent, rather than trickle release through the cycle. They are also usually wider than they are tall. Ideally, you want to find a pressure cooker that is as tall as you can because it increases the diversity of its uses and duration. A taller PC will be able to hold tall jars and bottles for grain, LC, and agar.
These off-the-shelf models generally top out at the same height as your average saucepan, with a capacity ranging between 4 and 12 litres. You’ll also find that these smaller, cheaper PCs boil off water much quicker than a PC that reaches textbook 121C, as they often vent more sporadically, have a smaller capacity in the first place or need cooking longer to sterilise. This may mean you need to top up the water part way through the sterilisation cycle, stopping the PC, adding water and then continuing the cycle once the PC is back up to pressure. This all takes extra time and energy.
If you get bitten by the mushroom growing bug, you will readily realise the limitations of these PCs, when compared with the bigger capacity, wider mouthed ones reviewed below. The question you need to ask yourself before you buy one of these is, ‘What will actually fit in here?’
PCs like these don’t inspire personal confidence either. They often feel flimsy and despite being perfectly safe, they will, seemingly violently, release steam making them loud and terrifying to someone who has never used a PC before! Before buying a new one, check your local Facebook marketplace, Gumtree and eBay for some bargain second-hand ones!
The Presto 23qt, model number 01781, is my workhorse and absolute favourite PC, but I’ll try to remain un-biased.
The American designed, Chinese manufactured PC is fantastic value for money. Due to Covid-19, the price and availability of pressure cookers have fluctuated phenomenally, however, Presto still remain the number one pressure cooker for mushroom growing, in my opinion. The Presto is approximately 29cm tall, 32cm in diameter and a capacity of approximately 22 litres. This design also comes in a smaller version of 16qts, about 15 litres.
The PC is stamped out of aluminium, not cast, so it is very light. When compared to the All-American 921 which has a slightly smaller capacity and when empty, is 8.2kg vs the presto at 5.6kg. It’s nearly 3kg lighter. This is something to consider if you have a fragile range such as glass or ceramic.
The Presto 23qt includes a pressure gauge as standard, as well as a pressure-lock system, preventing you from opening it whilst still pressurised. As standard, the PC comes with a 15psi rocker that sits on the vent. I have seen people weigh these rockers down with coins, however, there is no need since they achieve 15psi comfortably with the included rocker weight. You can also buy rockers for 5psi and 10psi, which isn’t required for mushroom growing, though good for preserving recipes! The newer models of the 23qt Presto has a variant with a steel insert in the base of the pot, this gives it the functionality to use it on an induction hob!
The Presto includes an aluminium Trivet which keeps your jars off the bottom, however, I designed my own Trivet as I don’t like my bags or Cordycep pots to be sat in water as they can bounce about.
There aren’t any.
It’s loud, quite loud in fact, until you get familiar with how the rocker works with your hob. It sounds like a steam train pulling off of a station, picking up speed. However, once you learn to manage the heat, it does soften into a gentle rocking chuff, or deafen you, one of the two.
Straight out of the box, I found several loose fittings on my Presto that needed tightening up, including the handles and pressure gauge. The Presto seals up with gaskets, though my first set of gaskets lasted me 100’s of cycles. As they age, they do leak and require more time to heat up and expand before they seal, so it’s always handy to keep a spare set of gaskets on standby.
Despite these few things, the Presto 23qt is a fantastic tool which will immediately outshine anything you’ve used before. This may be premature, but out of all the PC’s I am reviewing, this Presto 23qt is without a doubt, the best value for money. At the £100 mark you won’t find anything else like it on the market as of writing this. You will also need to add shipping and import duty to the UK, which will add another £50 to £150 on-top, that is if you buy it direct from Presto and arrange to have it shipped by a 3rd party company to the UK such as MyUS, since Presto only ship domestically.
The links below are to a few eBay and Amazon sellers of the presto. They vary a bit in price, shipping, and availability but all hover between £150 and £225 including shipping and import fees! If you find them cheaper on eBay make sure they include shipping, import duties and VAT too, otherwise your PC will be stuck in customs until you pay the duty and VAT on it and may incur additional processing fees!
The Hawkins BigBoy, model number JI-Q0PG-9YWZ, is the second cheapest PC that I will review today after the Presto 23qt. At 22 litres capacity, it is comparable in volume to the Presto, designed and manufactured in India from stamped Aluminium. The dimensions of the BigBoy are approximately 30cm tall with a diameter of 25cm and weighs around 9kg! Another one to think about If you have a fragile hob. The BigBoy comes in smaller versions of 14-litres and 18-litres too, but for this review I borrowed the 22-litre model from a friend! As a pressure cooker, the Hawkins is perfectly fine. The PC will reach a working pressure of 15psi, sufficient for the sterilisation cycle, making this PC suitable for mushroom growing.
The BigBoy is primarily designed for cooking large volumes of food and not for canning/sterilising jars and bags. What the Hawkins does well, thanks to its design, is conserving and reducing energy use. In order to get up to and maintain the 15psi required, the manufacturer claims the BigBoy uses a smaller amount of electricity or gas compared to a conventional PC. The whole design of the unit shows that the manufacturer really had safety on their minds.
Since most of us use our PC’s as a way of preparing the grain before we sterilise, it’s handy that the Hawkins has big, well made handles. These allow you to tip the grain into the sieve in your sink with ease and without burning yourself. You can hold one handle and then use the longer handle that the lid attaches to, to torque your wrist and pour. This is a great feature of the Hawkins that I really like.
Though many mushroom growers use this PC without complaint, the main issue for me is that the Hawkins BigBoy has a weird oval mouth design. The pressure cooker domes back in on itself about an inch around the lip of the opening and the lid seals from the inside out like a plane door. This means that the lid has to be turned 90 degrees so the oval won’t interfere with the body, then angled downward into the PC to allow you remove and insert the lid.
This requires around 1/5th of the PC to be empty in order to re-fit the lid. By the time you’ve got your trivet and spacers in, you’re losing a big portion of the PC’s capacity to unusable space. This makes the PC very safe but also inefficient in terms of capacity. Given the quality of most modern PCs which include safety valves and blow-out ports, this design is rather outdated. The PC also can’t be used on an induction hob.
The Hawkins is also without any type of gauge, so you’re dependent on your rocker-weight for the correct pressure. However, sterilisation can be verified with the use of some autoclave tape or by fitting a gauge yourself. It would also be a good idea to keep a spare gasket on standby for your model of Hawkins as this PC will run into the same problem of a leaky gasket.
Even though the Hawkins BigBoy has these disadvantages and is somewhat more expensive than the Presto 23qt, it can be found readily available across the world and is usually more frequently found on second-hand markets like eBay, Gumtree or Facebook Marketplace for half the retail price. Below is an affiliate link for an eBay advert for the Hawkins BigBoy. As of writing this, it’s on for around £190 including postage but doesn’t include import duties or VAT so these will need to be paid on arrival in the UK, I would expect another £40 to £70 for duty and VAT
The AA is an American designed and American manufactured pressure cooker. Like the others, it comes in several sizes ranging from 10qt to 41qt or 9.5L to 38L. For this review, I borrowed a friends… what a scrounger I am. The AA 921 is approximately 31cm tall with a diameter of around 30cm and weighs approximately 8.2kg, it has a capacity of 21qt or 19.8 litres. Unlike the other PCs in this review, the All American is made from cast and machined Aluminium rather than being stamped or formed.
The AA PCs are completely gasket-less around the seam. The way the AA seals is with a light smear of Vaseline or oil on the inner flange of the lid and mating portion of the body before each cycle, then by securing the 6 wingnuts evenly. This creates the air-tight seal, metal to metal.
This means the AA only has one ‘consumable’ part which is the over-pressure plug. On this model, the over-pressure plug is different since it’s an older version. However, on the newer AAs this plug will crack and distort over time and eventually need replacing. Fortunately, these plugs are inexpensive so it’s worth carrying a spare one
The main feature of the AA that I like, is its big and bulky sections are built to last. It’s refreshing in a throwaway society to see something with long-term use and a repair infrastructure designed into it. The machining quality of these PCs overshadows any other on the market. Besides, excluding the metal fatigue, I’m sure an AA PC from the 1930’s would still be serviceable today.
All AA PCs come with a gauge which reads temperature and pressure in both Metric and Imperial, a step-up from the standard pressure gauge, however, the temperature is just an assumption based on pressure!
The newer models of AA have a unique design with the rocker where you can choose 3 different pressures by rotating the rocker to the appropriate pressure stamped on the unit. Pretty nifty invention though unnecessary for sterilising mushrooms, it’s great for preserves! As you can see, the model my friend leant me is in need of a de-scale but still perfectly serviceable!
The All American’s bulk may be a disadvantage to some, this model weighs 8.2kg and the biggest model, the AA 941, weighs 15kg empty. Once full, it can double or triple the weight depending on your substrate. That is why many of the AA PCs instructions discourage use on fragile ranges such as glass or ceramic. This also means that you will either require a separate, large gas burner or a hot plate. However, you need to make sure that it’s not induction because the AA is not compatible with induction hobs!
The AA doesn’t come with plastic handles so moving the PC requires the use of tea towels or oven gloves, as it shouldn’t be moved with the handle on-top, rather the two metal ones on the side. If, like me, you use your PC for boiling grain too, you may guess that a pot this size would prove a bit of a faff to boil your grain and drain it without burning yourself! With the Presto and Hawkins, you have a plastic handle to grip making the operation smoother and safer.
Since the AA is gasket-less, it requires slightly more setting up and tinkering with as opposed to the ‘plug and play’ Presto. I feel this very mechanical process could be daunting to those who are uncomfortable with the idea of pressure vessels. Though unlikely, the possibility of setting it up wrong by incorrectly torqueing the wingnuts or lubricating insufficiently may be enough to turn people off of the AA. They may prefer a simpler interlock mechanism like the one that the Presto offers.
The great quality and features of the AA reflect in the price. For the average mushroom grower, dropping £300+ on a pressure cooker is a big outlay. Since these are only sold in the USA, the price is before shipping and import duty, this will add at least another £100 to £150 depending on the courier. As of writing this blog, they are also on back order until May 2021.
The all American is fantastic. It is built for heavy, repeated cycles over many years without the need for much intervention or maintenance. It may seem overkill to have such a thick and heavy beast when a Presto 23qt can do the same thing. However, subjected to the same cycles over time, I can see the Presto 23qt failing long before the AA is even run-in
That being said, I could afford 3 or 4 Presto’s for the cost of one All American pressure cooker. I ask myself, am I really going to burn through 3 or 4 Prestos in my lifetime? Everyone wants to look flashy and have the best gear, but I’d rather have 2 Prestos and some change to spend on other growing goodies. However, if one comes up second hand near-by, I’ll be on it.
All of these pressure cookers are perfectly suitable for mushroom growing. However, the off-the-shelf brands have a very quickly realised limitation, the Big Boy loses points on its poor capacity for its size and not having a gauge. The AA, while great quality, loses points on price and availability. This means the Presto 23qt, despite being a bit louder and having gaskets, wins this fight… for now. Keep your eyes peeled for my eventual Autoclave review.
As usual, for any questions feel free to comment below or message me in the contact section! If you do choose to click on one of the above links and buy your PC, I would greatly appreciate it. Those links are affiliate links, they cost nothing for you to click but I get a small commission on recommending the product to you.
Stay safe out there, the world is a bit nuts right now.