Drawn together: the pH meter

Categories: Behind the stalls

Award-winning blogger and Borough Market regular Ed Smith displays a talent for illustration as well as the written word, as he talks to stallholders about the tools of their trade. This month: the pH meter

Dave Holton, Blackwoods Cheese Company

We started Blackwoods Cheese Company in 2013, initially basing ourselves in an industrial unit in Brockley, south-east London.

Myself and a few mates had made cheese back home in Australia and wanted to introduce a Persian-style feta to the UK—what is now our Graceburn cheese—which is a really creamy and rich cheese made with cow’s milk, rather than goat’s or sheep’s. It’s also preserved in olive oil, which keeps it relatively soft and luxurious compared to the hard feta that’s kept in brine.

Since those early days, we’ve added a soft rind, lactic cow’s cheese called the Edmund Tew, and a fresh lactic cheese called William Heaps, plus curd and whey products too. We’ve also recently moved to the dairy farm that we get our milk on, setting up a production unit and maturation room just 20 metres from the milking parlour. Thanks to our new facilities, we’ll soon add a washed rind cheese and a few other soft cheeses to our offering.

All cheeses begin with the same four ingredients: milk, a lactic acid bacteria starter culture, rennet and salt. Whether you end up with a soft and creamy Graceburn or something like a hard, mature Montgomery’s cheddar, it’s still just a derivative of those four base things. How you deal with the variables around them determines what the end result is.

Butter fat content
Of course, the type and quality of the milk is really important. We use raw, organic milk from cows that are a cross of friesian-holstein, which is a classic dairy cow, montbéliarde, a French breed often used for cheese because of the amount of protein in the milk, and swiss red, whose milk has a high butter fat content that’s good for yield.

But there are other variables too, like the season, the temperature in your dairy and of the milk itself, the starter culture you use, and how long you leave the milk before adding rennet, cutting, draining, pressing and so on.   

It wouldn’t be possible to make the cheeses we want to on a commercial basis without understanding how and when to control the process. For a consistent, high quality product, we need to know what’s happening every step of the way.

One way we do that—perhaps the key way we do that—is through using a pH meter. There’s nothing glamorous about it; it really just looks like a calculator with a couple of probes dangling off it. But it’s an essential piece of kit. 

Target acidity points
A pH meter allows us to get a grasp of what’s happening within every batch of cheese. We have target acidity points for each cheese when we know we need to take the next step. Because variables change, by looking for a pH point rather than, say, a time measurement, then we can hit that target each time. The pH meter is vital for determining when to add the starter culture, then when to add the rennet, which firms-up the solids, and when and how to cut the cheese to separate the curds from whey.

Throughout the process, the acidity of the milk is increasing or lowering. It goes from a pH value of about 6.7 at the start, to finishing in the low fours—pH is logarithmic, meaning each 0.1 measure is 10 times more acidic than the previous one. The practical importance of this is that the rate of acidity change speeds up as it gets more acidic, and the frequency by which we monitor the milk and then solids reflects that.

Food production work like ours is relatively low-scale and definitely a real craft. But it’s a science too, and measuring and controlling the pH value is right at the heart of the process and the result.

You kind of get what you pay for with the meters. We started with a relatively cheap (but still pretty expensive!) model, but we kept having to re-calibrate it, so the one we’ve got now is pretty high tech and scientific. Worth it, though. Each of our batches of cheese begins with around 450 litres of milk, and we want to get it right every time.