Scientists believe they have come up with a formula to create the perfect bacon buttie.

The two most important aspects are crispiness and crunchiness, according to a new study.

It revealed the crunching sound while eating rashers should ideally measure 0.5 decibels.

They should also break when 0.4 Newtons of force is applied through chewing, the researchers said.

Butties were tested using a high-tech computer that measures food texture, while panels of 50 volunteers judged the butties for taste, texture and flavour.

Four scientists at Leeds University spent more than 1,000 hours testing 700 variations of the traditional bacon buttie.

Variants included: different types and cuts of bacon (smoked, unsmoked, streaky, thick cut); cooking techniques (frying, grilling, oven cooking or microwaving); types of oil (sunflower, olive, vegetable); and a range of cooking times at different temperatures.

Dr Graham Clayton, who led the research team, said: "We often think that it's the taste and smell of bacon that consumers find most attractive.

"But our research proves that texture and sound is just, if not more, important."

:: British households spend more than ยฃ1bn on bacon every year and it remains the UK's most frequently eaten meat.

The 'perfect' bacon buttie formula:
N = C + {fb(cm) . fb(tc)} + fb(Ts) + fc . ta

N = force in Newtons required to break the cooked bacon.
fb = function of the bacon type.
fc = function of the condiment/filling effect.
Ts = serving temperature.
tc = cooking time.
ta = time or duration of application of condiment/filling.
cm = cooking method.
C = Newtons required to break uncooked bacon.

Making the 'perfect' bacon buttie:
:: Cut two slices of white farmhouse bread, 1 to 2cm thick.
:: Take two or three rashers of back bacon.
:: Place under preheated oven grill for approximately seven minutes on high (preferably 240 degrees).
:: Turn once during cooking.
:: Add sauce to taste.