Until this year (2016), I have been roasting sio bak in cheap, “portable” (or table-top/ counter-top) ovens ranging in size from about 30 litres to 45 litres.
I did notice that with the larger ovens, the results were a little easier to predict, but even the 45 litre oven would be “temperamental” at times.
But when I renovated the Toa Payoh flat, I got a full-sized built-in oven. I think it was about 60 litres. Or bigger.
And I’m getting more consistent results for the sio bak now.
Now the times and temperature produce more consistent results. Thirty minutes at 180C would get the salt crusted consistently. Then 3 hours at about 120C (low and slow) would give me a tender roast. Raising the temperature to about 180 after that 3 hours produces crackling within 10 minutes (if it has not crackled by then), and the roast is done in within 20 minutes. Usually less.
[Note: The temperature and times here are for my current full-size oven and may differ from the temperature and times given in my previous post.]
There is a greater certainty and confidence.
Part of the reason is that a larger oven has a more even temperature, with fewer “hot spots”. Also the full-size oven has better insulation so the heat and steam is better retained. So the cooking temperature over 3 hours is more stable and predictable.
I also wonder if my opening the oven door at about the 2.5 hour mark matters. Firstly, there is a loss of steam at the time. Is that important for the development of the crackling?
I think this “interest” will consume me. Or rather, I can never really be sure that I have “mastered” sio bak.