use factorial experiment technieques please.

Early in the manufacturing process, milk is put in a vat and a 'starter culture' of bacteria is added. After several hours, an enzyme called rennet is added to the milk. This causes the milk to coagulate so that the solid 'curd' may be separated from the liquid 'whey'. The curd is then used to make the cheese. The CTO wants to determine the optimum conditions to ensure the curds formed have as smooth a consistency as possible. As well as the quantity of rennet added, the CTO suggests that the time at which the rennet is added, the stirring speed and the amount of starter culture bacteria added may affect the smoothness. Explain how these variables should be investigated and the results analysed to determine the optimum conditions. Your focus should be on techniques from the module as opposed to details of experimental procedure. Explain why the quantity of rennet may differ under the optimum conditions from that determined by varying this variable alone. Discuss the difficulties of performing this investigation and how these may be reduced